Depth of Field, Depth of Focus, and Film Flatness

[steve simmons]

Depth of Field, Depth of Focus, and Film Flatness

Ok, I think we can all agree that depth of field is an important concept in theory and in reality when using a large format camera.

Now, in both theory and reality there is one plane of sharp focus in any photograph. The location and orientation of this plane depends on the distance between the optical center of the lens and the film plane and the orientation of the subject plane, the film plane and that of the lens board (the Scheimpflug Principle). What appears to be in sharp focus in front of and behind the plane of sharp focus is really a function of the size of the circles of confusion. If these are small enough then those parts of the image will appear to be sharp when the photograph is viewed from a normal viewing distance. This area of apparent sharpness in front of and behind the plane of sharp focus is considered the depth of field. Depth of field is dependent upon the reproduction ratio (the relative size of the image on the groundglass/film plane and its size in reality) and the f-stop being used. As the reproduction ratio approaches 1:1 (closeup work) the depth of field will decrease. As the f-stop number becomes larger (meaning the size of the aperture gets smaller) the depth of field will increase.

What is depth of focus? Depth of focus is the space behind the lens where the film plane position can vary slightly and still not cause any loss of sharpness. Sometimes, people have felt that this space can makeup for a slight variation in film position and lack of film flatness. Depth of focus does increase as the lens is stopped down. To some extent, the increase in depth of focus matches the increase in depth of field as the lens is stopped down. Depth of focus also increases as the camera and lens get closer to the subject: i.e. as the reproduction ratio begins to approach 1:1. Depth of focus is not affected by focal length of the lens. However, if the subject area completely fills the depth of field area the depth of focus becomes so small that there is no tolerance for any variation in the film’s position, thus depth of focus can not really be used to make up for an incorrectly aligned plane of focus (mis-aligned film and lens board planes) or a poorly positioned piece of film.

So, what does this all mean. Well depth of field is an important concept in theory and reality. I think we can all agree on this opinion. However, depth of focus really becomes an academic concept that is not of much use to use when we are making a photograph IMHO. In most situations the depth of focus is so small as not to be an effective aid to us. One thought about the importance of depth of focus is that of the four primary books on large format technique, only one of the books even mentions depth of focus.

So, how does this relate to film flatness in various film holders. Well in my 30 years of using large format and using every type of holder I could find, and in my knowledge of hundreds or working large format photographers doing the same, an unsharp image due to poor film flatness in a holder is an extremely rare commodity. Many studies have been done looking at the effective film flatness of various holders, whether or not they have a pressure plate, etc. and there are differences certainly. But the key question is do these minute variations make any difference to a photographer making a photograph. Rarely and only in the most extreme conditions is the answer. We can debate these minute differences, we can continue to do studies, etc., etc. but in reality they all work except in an occasional damaged holder situation or damaged camera back scenario.. Camera and film holder mfg's have worked with this tolerance requirement for years and years and years and have effectivley solved this probelm so we generally do not have to worry about it. Relax and photograph

Steve simmons (www.viewcamera.com)

[Aaron van de Sande]

It is a big issue now more than ever because of the non-standard backs that you get with ULF film sizes, and the resurgence of ULF camera use. Many people are cobbling together backs from different cameras.

[Eric Biggerstaff]

Thanks Steve,

Interesting post.

[steve simmons]

Actually, here is a disclaimer. Above 11x14 the AINSI standards for film holders were never fully implemented so there may be some variation in these larger sizes.

steve simmons

[Sam Crater]

So - here's a question. We large format photographers usually shoot at f16 or smaller apertures, and I have seen that film flatness is not an issue for sheet film holders at those apertures. However, for some applications (aerial is the obvious one) it might be helpful to use much larger apertures. So at what f stop does 4x5 film flatness start to be an issue?

I would say that if you're trying to answer that question you need to grapple with the concept of depth of focus. My point is, people have different interests, causing them to need to understand and quantify different things. You can correct them saying 'that concept is not important' but the truth is that's an oversimplification.



By the way, I really would like an answer to that particular question...

[Michael Gordon]

Relax and photograph

Hear, hear! I realize that photographers come from all sorts of backgrounds, yet I'm continually amazed at the level of minutiae delved into and argued about on this forum. Photography - even with a view camera - doesn't have to be as complex or difficult as many of the posts on this forum might lead one to believe.

[QT Luong]

"Unsharp" is a relative term. I will give an example from the 35mm world. Prior to the relatively recent introduction of full-frame 35mm digital sensors, complaints about Canon wide angle zooms being unsharp were relatively rare. However all of a sudden, everybody can easily look at the pixels, and there is almost a consensus that they are lacking. If high-quality scanning becomes affordable in LF, the same could happen.

Working professionals are not necessarily concerned, or even aware, of image quality issues, because technical image quality (beyond a certain threshold of "good enough", which in my experience, is quite low) is way down in the list of priorities that makes one professionally succesful.

[steve simmons]

""So - here's a question. We large format photographers usually shoot at f16 or smaller apertures, and I have seen that film flatness is not an issue for sheet film holders at those apertures. However, for some applications (aerial is the obvious one) it might be helpful to use much larger apertures. So at what f stop does 4x5 film flatness start to be an issue? ""

There is not an absolute answer to this as it depends on the reproduction ratio. With aerial, assuming you are several hundred feet in the air (or more) the reproduction ratio will be quite small and depth of field will be pretty good (I can't give you the math becasue i do not know the film plane to lens and the lens to subject distance). It will also depend on how much you enlarge the image and how closely you look.

Unless you have a measurement of all these distances this is an impossible question to answer.

It all comes down to circles of confusion. This is a gradual in and out kind of thing.

steve simmons

[BrianShaw]

Do these formulas help?

http://www.matter.org.uk/tem/depth_of_field.htm

[Hiro]

Thank you, Steve, for an informative post. Connecting all these concepts may be a second nature to you and other experienced photographers (in any format), but the well-thought explanation was very helpful for me.

There are many things that could cause problems in the field (or elsewhere). For example, I always wonder "How in the world can this thing stay in good focus?" every time I insert a holder and, particularly, pull the tab of a Quickload packet. Although I've shot only 200 or so LF films, the focus came out OK at least by my standard (which may change in the future) except for some obvious human (me) errors.

Relax and photograph---That's what I seek and actually do with LF. Mysterious light leaks, wrong meter ISO setting, missed light because I wasn't quick enough to set up... Yes, it's all maddening, but it ruins the whole purpose of shooting LF for me if I get too concerned. I (try to) shrug and say "What the f&%#." Alcohol helps a bit, too.

[tim atherton]

It all comes down to circles of confusion. This is a gradual in and out kind of thing.

ahh - like making love to a beautiful woman

now it's starting to make sense

[robc]

"However, if the subject area completely fills the depth of field area the depth of focus becomes so small that there is no tolerance for any variation in the film’s position"

That would include a planar subject as stated previously.
It would also a include a subject focussed at infinity such as the horizon, something which many photographers find difficult to get sharp without using tilts, which was also stated previously.

--

"There is not an absolute answer to this as it depends on the reproduction ratio. With aerial, assuming you are several hundred feet in the air (or more) the reproduction ratio will be quite small and depth of field will be pretty good"

Aerial will fall into both planar and infinity(unless at very low level) and since the plane (pun intended) will be moving, a wide aperture to minimise exposure time is highly probable thereby making depth of focus critical. No wonder the Linhof vacuum back was used for this application.

--

The articles on LFPF here (http://www.largeformatphotography.info/holders.html) give examples of several people who have had problems with bad film holders causing uneven
focus.

--

I think the light is dawning. Let me know when the sun's up.

[Sam Crater]

Unless you have a measurement of all these distances this is an impossible question to answer.

Okay, say I have a lens to subject distance of 500 m, a focal length of 135 mm (and a lens to film plane distance of 135mm,) and I want a COC of 0.1 mm on the negative.

[steve simmons]

How did you decide on .1mm as the size of your CofC?

steve simmons

[Leonard Evens]

Steve's discussion is a good general analysys of the relation between depth of field and depth of focus. What he says is substantially correct in most practical picture taking situations, although some of us may differ about its universal application.

I have two minor comments.

First, depth of focus could be important in the one situation where its definition applies unambiguously: when the subject is confined to a single plane or very close to one. It tells us when slight errors in flim placement, film flatness, and focusing may become innocuous if we stop down (but not so far that diffraction is an issue).

Second, Steve may have given the impression that the only relevant parameters affecting depth of field are "the reproduction ratio (the relative size of the image on the groundglass/film plane and its size in reality) and the f-stop being used", as well as the circle of confusion he mentioned earlier. Depth of field depends on one addtional parameter when expressed this way. Thus, in addition to the three mentioned, one could choose any one of lens focal length, subject distance (to exact plane of focus), or image distance, all of which are related if magnification is constant. If the exact subject plane is fairly close to the lens, then coc, relative aperture and magnification suffice for all practical purposes. But for relatively distant subjects, the fourth parameter is essential. I mention this because it is a widely held misconception that depth of field is independent of focal length if magnification is kept constant. I've never understood why people hold this belief so firmly when it is patently false for distant subjects.

[John_4185]

I would say that if you're trying to answer that question you need to grapple with the concept of depth of focus. My point is, people have different interests, causing them to need to understand and quantify different things. You can correct them saying 'that concept is not important' but the truth is that's an oversimplification.

You go ahead and grapple. Whatever you do, don't make another picture until you are completely satisfied with an answer.

Sheesh.

It ain't Rocket Science (and, BTW, we have at least one Rocket Scientist here.)

[Sam Crater]

You go ahead and grapple. Whatever you do, don't make another picture until you are completely satisfied with an answer.

Oog. I should never have said anything. My sincere apologies to everyone. I won't make this mistake again.

[John_4185]

Oog. I should never have said anything. My sincere apologies to everyone. I won't make this mistake again.

No no! My apologies! (Sam, let's trip all over each other in escalating apologies!)

I overstated it because, well, I used to be a perfectionist. (DQ here will tell you I still am!)

[David Karp]

Tuan,

I think that "good enough" is quite client specific. I used to work for a company that had pretty demanding requirements for their professional photographer. Although much of what he did for us was catalog work, it had to be very good, because our customers were very discerning. High quality catalog photographs were both attractive and informative. In addition, the architectural photography work he did for us had to be top notch.

Pertinent to the technical discussion, I suppose that the size at which the images will be used is an issue. For most commercial applications, the enlargements are probably not too large, and that was often true of our work too. For us, a full page or two-page spread in a catalog was about as large as most photos would ever get. Similarly, all of the work that I have done using a Quickload and a 545 holder was enlarged to no more than would fit on an 8.5x11 inch page. That would, I suppose, make a big difference in the acceptable circle of confusion. If all of the photos would have had to be 16x20 or larger, then perhaps we would have run into a problem using a Quick or Ready Load in a Polaroid holder. (Even so, those transparencies always looked pretty darn sharp under the loupe, at least to my eyes. I would not have been worried about enlarging them to that size, or bigger, but I might be wrong about that.) At the old company, when we did want a large photo (for use at a trade show or the like) we tried to use LF shots to make sure we had the best looking image possible.

At the other end of the scale, high volume catalog work and other similar professional photography does have to be just "good enough" and what "good enough" is is often just passable (and possibly quite below the capability of the photographer). To be fair to the photographers, acceptable quality is the client's call, and it is the professional's job to deliver what the client wants. Then, if the photographer delivers a higher quality photo that took longer and resulted in less production (volume), they are costing the client more $ than it needs or wants to pay, and doing the client a disservice. From what I have seen, some of the other things that go into a professional's success include personality, customer service, availability, flexibility, and all of the many things that go into making other non-photographer entrepreneurs successful.

[John_4185]

I think that "good enough" is quite client specific. [...] From what I have seen, some of the other things that go into a professional's success include personality, customer service, availability, flexibility, and all of the many things that go into making other non-photographer entrepreneurs successful.


I'm a Minnesotan. We invented Nice. Any out-of-focus (hereon OOF) problems we get, we can NICE right back into focus. It's our little niche in the universe. It works on everything but coffee. Don't drink our coffee.

[Sam Crater]

jj,

Thanks, no offense taken if none was intended.

Steve,

Only because I thought .1mm was the conventional standard for 4x5. Maybe .05mm would be better.

[Sammy_4293]

Steve,

I thank you very much for this. I am a new LFer and have a question for you regarding the reproduction ratio. I have a tool named Rodenstock Depth of Field Calculator. There is a setting called Scale of reproduction. There are 1:1; 1:2; 1:5;1:10; 1:20; 1:infinite. Could you teach me how to set up the Scale of reproduciton?

Thanks

[David Karp]

Nice won't get an out of focus photo back into focus. Of course, that was not what was said or close to the the point of anything mentioned in the post, which was responsive to Tuan's comment regarding the quality of some professional photographer's work.

Given two photographers equally capable of delivering in focus photographs, most marketing professionals I have known would rather work with the one with the easy to work with personality, rather than the jerk. And if the quality between the two was close enough, even with the less talented photographer who was easy to work with instead of the jerk. And if they had to work with the jerk for a while, they would certainly be looking for someone to replace the jerk ASAP.

[Dave Henry]

Dave, you have hit the nail squarely on the head with your last paragraph. In the freelance side of my life, I've made a good living from clients that were tired of babysitting their previous photographers. Nicely stated.

[Jerry Fusselman]

Leonard wrote, "it is a widely held misconception that depth of field is independent of focal length if magnification is kept constant. I've never understood why people hold this belief so firmly when it is patently false for distant subjects."

This is technically true, but I like Steve's way of looking at it better. It is true that when you increase focal length while holding f-number and magnification constant (and focus on the same subject), you get a little more depth of field in front (of the plane of sharp focus) and less depth of field behind.

But this only occurs because we are accustomed to the traditional definition of depth of field. If we used Harold Merklinger's object-field definition instead, which I generally prefer anyway, then Steve's statement is exactly correct (Of course, I am ignoring diffraction and assuming a perfect film and lens).

For example, from p. 37 of Merklinger's "INs and OUTs of Focus": "If we do change lenses (or zoom) so as to maintain the same image magnification as the camera-to-subject image changes and keep the lens (or lenses) set to the same f-number, the depth of the zone of acceptable sharpness does not change."

[William Mortensen]

A couple of questions... Would it be accurate to simplify the terminology by saying depth-of-field defines the area of (apparent) focus in front of the lens, while depth-of-focus is the same phenomenon behind the lens?

Second question: When making an enlargement, is the depth-of-focus up where the negative is and the depth-of-field down where the photo paper is, or is it the other way around? (BTW, considering how out-of-alignment many enlargers are and how much some negatives curl in the carrier, this could be every bit as important as when out shooting.)

[Jerry Fusselman]

Mark, I will attempt some answers to your two questions.

I have nothing against your way as stated in the first question. For example, in 1-to-1 photography without movements, the size of the depth of field and depth of focus are equal.

You can imagine the light going in either direction. Therefore, there is no fundamental geometric distinction between depth of field and depth of focus. You can say that the paper lies in either depth, for the mathematics does not distinguish between the two.

When Steve wrote, "Depth of focus is the space behind the lens where the film plane position can vary slightly and still not cause any loss of sharpness, " he maybe made a little misstatement or simplification of language. Instead of no sharpness loss, he really meant to refer to acceptable sharpness loss. The circle of confusion determines both your depth of focus and your depth of field, so depth of focus is a concept based on acceptable sharpness loss rather than no sharpness loss.

[Kirk Keyes]

I think Mark just made two excellent points. I think his first one really brings the whole issue into focus. (Sorry for the pun.)

For every photograph that has some image area that is out of focus, the photographer has just had a bad encounter with insufficient depth of focus. You may want to completely blame depth of field, but you can't. Depth of field and depth of focus are really the same principle being applied to opposite sides of a lens. And while it is appearant from these recent threads that a majority of photographers do not know or think about depth of focus (based on book references), it most certainly is an optical principle that leaves it mark on every photograph.

The issue of having insufficient depth of focus is not going to be seen if the camera/lens system is properly adjusted and the alignment of the subject, lens, and film planes are sufficiently close for a given f/stop / circle of confusion / enlargement. But when one of them is poorly adjusted, then we often times will just attribute the focusing errors to "bad focussing". Well, it's just as much insufficent depth of field as it is depth of focus.

If the depth of focus was always infinitely large (or even sufficiently large), then we would never have to worry about the position of the ground glass or the flatness of the film. But, unfortunately it's not infinitely large. If depth of focus was always zero (infinitely thin) then we would probably never get any image to appear in focus. I guess we should feel lucky that it is somewhere inbetween, and large enough that it does not make itself very appearant. (It's kind of neat that it is proportional to the depth of field.)

But when we have a camera that does not have the ground glass in the same position as the film, then our depth of focus issue may be readily appearant. If the error is grossly off, then it will be quickly obvious to the photographer that something is wrong, and hopefully the error will be corrected. But what if the error is marginally off? A lot of wasted time and frustration may be the result of this. This is all a result of depth of focus. It's kind of silly to say it's a non-issue and can be completely ignored.

Mark's second issue brings up a lot of situations that I'm sure we've all encountered with while printing - negative bow, negative stage misalignment, lens stage misalignment. How many people here use glass negative carriers? Why - because you couldn't reliable get all of the image into focus? Especially with big enlargements? Well, this is completely related to depth of focus. Popped negs, misalignment - both decrease the amount of depth of focus that we have available to make an in-focus print. Again, to say it is a non-issue and completely ignored is a kind of silly point of view in my opinion.

Mark, I too like to think of the depth of focus at the film when enlarging, and depth of field at the paper. I don't know if there is an actual convention to the nomenclature for it.

Kirk - www.keyesphoto.com

[Kirk Keyes]

Jerry wrote:

When Steve wrote, "Depth of focus is the space behind the lens where the film plane position can vary slightly and still not cause any loss of sharpness, " he maybe made a little misstatement or simplification of language. Instead of no sharpness loss, he really meant to refer to acceptable sharpness loss. The circle of confusion determines both your depth of focus and your depth of field, so depth of focus is a concept based on acceptable sharpness loss rather than no sharpness loss.

I've certainly seen this come into play in the real world. While trying to get a shallow depth of field in a photograph, the area of subject that I had focussed for, using the "find near and far subject position and focus in the middle with the appropriate f/stop / circle of confusion" technique, I saw that after I processed the film the near and far focus we shifted slightly from where I was expecting them to be.

Was it a problem with a misalignment of the ground glass? I've never seen issues that would suggest a misaligned gg. Was this a problem with focussing? I assume not as I have a mm scale that I use for focussing. But a slight misfocus due to any reason can push one side of the image out of the acceptable circle of confusion on the negative.

Whichever issue you want to attribute the slight difference in expected focus range from actual focus range, it is most certainly was an issue with depth of focus.

Kirk - www.keyesphoto.com

[Oren Grad]

Umm, just a gentle reminder to Steve that he published in the March/April 1996 issue of his own magazine, an article entitled "A Battle of the Bulge: Sheet Film Holders", in which author Cervin Robinson outlined a scenario in which depth of focus matters (although he didn't use the term), and proceeded to report the result of tests of several different types of film holders for accuracy and precision of positioning of film relative to the ground glass. The author's conclusion, BTW, was that the slop in the positioning of film by different holders was of sufficient magnitude to be worth worrying about.

[Kirk Gittings]

"is a kind of silly point of view in my opinion."

Can we try and stay away from this kind of language. Calling someone's opinion silly is where the flame wars begin. We don't have to put each other down to have an intelligent discussion.

[Kirk Keyes]

Sorry, it was just my opinion...

[bglick]

Steve.... In the cancelled post, I tried to be a peace maker. In that thread (which was temp. removed by the moderator), I was amused and confused how one person could possibly have so many enemies. This post, which is not a question, but rather your version of a continuation of the cancelled thread, clearly demonstrates your struggles with 1) admitting being wrong, 2) offering credit to posters trying to help you.

In all fairness Steve, you could have at least credited several of the posters who "beat their brains out" in the cancelled post to first, try to convince you the concept of "depth of focus" even existed. Then after you blasted them for such, they still took the time and energy to educate you on this subject. At first, you did not acknowledge the topic of "depth of focus", next you took the position, it only exist for anal photographers, and now in this post, it exists...... but you explain why it's not signficant. As an author in this field, it's my opinion you should at least give credit to those who educated enough to write this post. Gestures like this may reduce the enemy count and possibly increase the number of buyers of your book and magazine..... it's just a suggestion, it's obvious that, me and you have two different mindsets on how to treat others.

Now, based on what I learned about your "mode of operation" in the last cancelled post, I do not expect a response regarding any subject matter that does not present you, or your opinions in a favorable manner. In addition, this post was not a question like most, it was an attempted tutorial, so I am only making comments on your tutorial.

Although I do applaud your recent R&D on this subject matter.... it appears you did more then make phone calls to a few friends who knew nothing about "depth of focus" subject, and therefore dismissed the subject as being virtualy useless. This post is simply trying to further that position. Although your understading of "depth of focus" has increased, your tutorial, in my opinion, is too much of an oversimplification and in some areas the vagueness makes it border on being wrong. You continue to refuse to express the relative nature of your desciptions in numbers. I understand your approach, reduce all math and any detail down to a few vague descriptions. So, I will do my best to stick to your premise....

> What appears to be in sharp focus in front of and behind the plane of sharp focus is really a function of the size of the circles of confusion.

"appears" is rediculously vague for a writer of technical books, but it would require a tiny bit of simple math, which you do not include, so this describes nothing. Now, I would state this as, the size of the Circle of Confusion (CoC) is often a function of the "defocus" principle, i.e. relative position of the near or far subject distance compared to the point of exact focus. Of course, the CoC can be effected more, or less, by lens MTF performance, aperture diffraction and depth of focus. The point being, Depth of Field alone, is rarely EVER the only determing factor of the CoC diam. This is NO small detail.



> If these are small enough then those parts of the image will appear to be sharp when the photograph is viewed from a normal viewing distance.

"normal" Now, I know you don't like using numbers, but how can you define normal for us? "appear sharp" what is sharp? as compared to what?



> What is depth of focus? Depth of focus is the space behind the lens where the film plane position can vary slightly and still not cause any loss of sharpness.

Your statement is not completly wrong, just too vague to be clear. More accurately, Depth of Focus, is the the region in front of and behind the focal plane where the diameter of the light cone is smaller than the permissible circle of confusion.

> However, if the subject area completely fills the depth of field area the depth of focus becomes so small that there is no tolerance for any variation in the film’s position

First, subject area always fills the depth of field area, otherwise it would not be considered depth of field area, as depth of field area never includes "air", as lenses do not focus on air. Point is here, the only thing that effects Depth of Focus (film play as you call it), is the f stop, or effective f stop for close up photography. The film plane doesn't have a clue what is happening on the other side of the lens, or depth of field.



> thus depth of focus can not really be used to make up for an incorrectly aligned plane of focus (mis-aligned film and lens board planes) or a poorly positioned piece of film.

Again, not sure if your wrong or right, as I read it 5x but still don't understand what you wrote..... I will offer, Depth of focus is not a tool to correct for any physical shortcomings in the camera system, instead, Depth of Focus simply defines the region in front of, and behind the focal plane, where the diameter of the light cone is smaller than the permissible circle of confusion. The definition can not be shortened and remain clear. I still have not used one single number, just short sentences as you like.



> In most situations the depth of focus is so small as not to be an effective aid to us.

What? This is contradictory. The fact the Depth of Focus is "so small" explains the potential it has for being the bottleneck in the entire optical chain! The fact it is so small is what makes it so dangerous, vs. "not to be an effective aid" ??? Steve, I truly beleive you have grasped part of depth of focus, but are are not applying it properly. You have the tail wagging the dog here!



> However, depth of focus really becomes an academic concept that is not of much use to use when we are making a photograph IMHO.

Well, here is how I would have worded this...... Depth of focus becomes an academic concept that is not very useful when using a box type roll film camera (MF or 35mm) and shooting at f stops above f 4.0 (based on Zeiss study), this assumes not using a roll film back with reverse rollers which can alter the film buckle dramaticaly when the film is left in the back more then 5 minutes and film is advanced.

However, when using a view camera, Depth of Focus should be something to consider as the cameras size and floating standards can put more demands on depth of focus requirement. Also, the film holder and gg alignment positioning must be considered as unlike box cameras, the film holders and cameras are rarely made by the same company and often not of the same vintage before all cameras / film holders used the same set of standards. Depth of Focus shortcomings with view cameras can surface under these scenarios.....



1. the front and rear standards are not well aligned and square at all corners. The lens board is not square to the front standard. Once again, older cameras can easily become out of alignment, as well as those knocked around in backpacks, and those, such as Benders (and others) which simply have poor manufacturing tolerances to begin with.

2. The gg/film plane alignment error is close, or outside the depth of focus region. (to allow for other shortcomings) Often an issue with mixing different roll film backs of different vintages on view cameras of different vintages, as well as using older film holders before that maker complied with ANSI standards (which assumes the camera complies also) Steve you forget how many people use vintage gear, specially hardcore hobbiest.

3. You shoot at low f stops, which decreases the depth of focus region. Stopping down, increases the depth of focus, but at the expense of diffraction and shutter speed. So not always such a wise choice. This is especially true of people using the newer digital lenses with film, whereas their MTF's are optimised at f8 - f11.

4. Focussing at infinity and using lower f stops then one is used to, suddenly, depth of focus shortcomings can appear.

It should be noted, that Depth of Focus shortcomings when photographing scenes with a large amount of depth of field will not always be apparent, as sometimes the alignment errors simply move the point of exact focus in front of, and behind the focal plane. However, when photographing a scene with very small Depth of Field, or none, such as a graffiti on a brick wall, the same camera / lens set up that seemed flawless, can suddenly produce images that are shockingly out of focus. (Rob tried to explain this several times in the cancelled post)



> One thought about the importance of depth of focus is that of the four primary books on large format technique, only one of the books even mentions depth of focus.

As Rob, Brian and many others pointed out in the cancelled post, the fact a given subject matter is not covered in 3 books you chose to select, should not dismiss it as a valuable piece of information to photographers in the modern era, armed with spreadsheets, programmabe calculators, higher education, etc. etc. For example, in your book, you couldn't have mentioned it, since you did not know it existed. Maybe this is the case with the other 2 authors you mentioned? I personaly would never dismiss something as "not useful" if myself and 2 other people were not aware of its existence? What about all the other photography books which are much more thorough then the books you mentioned? Are those 3 books the Golden standard of photographic knowledge? What about literature that goes back to the late 1800's? All useless, since a few short, low production books don't mention it? I just don't grasp your reasoning, although I keep trying.

> and in my knowledge of hundreds or working large format photographers doing the same, an unsharp image due to poor film flatness in a holder is an extremely rare commodity.

Well, in my less then 30 years of doing this, and many LF photographers I know, I have seen the Depth of Focus issue ruin a lot of images, waste a lot of money on film and travels and upset several people. Are the photographs usable? Sure, but they fell way short of the expectations of the photographer. In addition, there is many photographers that may not know they even have the problem, instead, it just limits the enlargement potential of some of their work, sort of a "reverse engineering" solution to a problem they were unaware of.



> Many studies have been done looking at the effective film flatness of various holders, whether or not they have a pressure plate, etc.

Yes, one in paticular was done by Zeiss in the mid 80's. They concluded film flatness is a major issue, and the sharpness of lenses was now being limited by film flatness in MF cameras. This was less of an issue in the earlier days in photography, as the diam of Coc was more relaxed vs. today. The study also reviewed film buckle on reverse rollers which became a severe issue at f 8 or lower and overall film flatness was becoming a major issue at around f 4.0 - 5.6 (from memory). Now, does this dismiss the problem for LF shooters since we shoot at f 16+? I am sure in to defend you position, you would think it is a reason to dismiss such. But in my opinion, NO! Why? Because a view camera has two major shortcomings vs. the MF box camera when it comes to film alignment / flatness. MF cameras are of box design, wheras the lens is always fixed at ONE position, eliminating loose, floating, front and rear standards. Sheet film can buckle as it's not held tight at both ends like roll film, it also can be prone to gravity when pointing the camera downwards.

To benefit some readers Steve, I am sorry, but I feel compelled to introduce a few numbers.... What is the difference in the Depth of Focus at f 5.6 vs. f 16 for non-close up photography? I will use the same CoC for the same enlargement factor of each....

f16, .033 CoC = .50 mm in either direction of focal plane

f5.6, .033 Coc = .19 mm in either direction of focal plane

.31 mm difference in allowable depth of focus. This is equal to the thickness of 3 pieces of standard 20lb bond copy paper. Now, hold 3 pieces of paper between your fingers and try to consider if you feel a view camera, with all it's physical slopiness, film buckle, focussing errors, etc, (vs. solid Hasselblad type design) can be off by this amount. If so, then you have reached the same conclusion that Ziess had, film flatness / alignment at the focal plane is an issue. Now on the other hand, one might consider the fact Steve and his 100's of friends never experienced this in 30 years as more compelling evidence. Everyone can judge on their own.



> But the key question is do these minute variations make any difference to a photographer making a photograph. Rarely and only in the most extreme conditions is the answer.

And what tests are these based on? Are these tests superior to the Zeiss tests? The LF community never had the benefit of the MF community whereas larger makers such as Ziess, hassy, etc, once had huge revenues to justify all this R&D. The LF camera makers were always spread out over many vendors, making each of one of them very small on a relative basis vs. MF camera makers. So most all tests are often of the home brew variety. But in this case, just applying some common sense can go a long way, even if one has to use a few numbers to grasp the relative nature of the subject.



> We can debate these minute differences

Steve, really, how do you define "minute" when you refuse to apply numbers to anything? I offered you a slew of examples in the cancelled post, which you chose to completely ignore, which is fine by me, but as an authority in this field, how can you continue to write with such vagueness when most of your customers are willing to arm you with the right information and make you look like a hero? I just don't get it. I hope, I have provided some "relative feel" to this problem for those intersted. For those not interested, as Steve states, relax, go photograph. Maybe these issues are of no concern today, but what happens when someone changes to close up photograpy or uses sharper lenses, slopier cameras, ULF, etc. etc.

As Brian and Jorge pointed out so clearly in the cancelled post, as an author, why don't you arm your readers with accurate information, and allow them to make their own decisions whether a paticular subject should concern them. Why write vague descriptions, with no references, nothing relative to what is known, and then conclude, if it's not an issue with you and associates, and it's not covered in a few books, then, everyone can relax, and go photograph. ???

I feel the entire DoF, Dof, gg/film alignment issue, are all equally important regarding on-film resolution, which is one of the reason many people migrate to LF photography. There is many very knowledgeable posters on this list. I would suggest to the moderator to have one of these posters prepare a tutorial that explains these relationships in detail and have it posted on the front page of this forum, just as other important topics have been covered. I would hate to have future users of this forum research this subject matter by referencing threads such as this, as the information is too valuable to be dismissed so quickly by someone who just discovered it a few days ago. And unlike digital photography, this issue will remain with us for as long as film exist.

[bglick]

When writing my lengthy post, many others responded in that time, so I apologize if some of my post was redundant of others above.

Oren, I find your post so entertaining, how can this be? Was Steve the author of the magazine back then? If so, this needs to be entered into the post which was cancelled....

[Jerry Fusselman]

Well, it is obvious to me that depth of focus is a useful concept. It led me to fix my roll-film holder rather than assuming I made some sort of error in technique. After fuzzy results, I wasted a roll of film and looked at it in my roll-film holder---I could see that it was clearly outside of my depth of focus, and therefore needed to be fixed.

[William Mortensen]

"Mark, I too like to think of the depth of focus at the film when enlarging, and depth of field at the paper. I don't know if there is an actual convention to the nomenclature for it." --Kirk Keyes

Kirk- Actually, I think I'm leaning towards the negative side being on the depth-of-field side, as that is the subject the lens is focused *on*. The projected image would be at the depth-of-focus location, as it is with the camera film plane. Not that the nomenclature matters that much...

BTW, I enjoyed your website, but it needs more b&w work!

[neil poulsen]

One can try to think in broader, more general terms, and it's also possible to speak in specifics by citing numerical examples.

Both add value. On the one hand, it helps to understand something by making a few calculations. But I think that in the application of these moderately complex principles, we must ultimately arrive at some generalizations to guide us in the field. If we were out in the field with computers, we probably wouldn't be shooting LF, because we'd be tethered to a digital camera.

As I said, I think that both approaches add value.

[Henry Ambrose]

It appears to me that when dealing with Depth of Focus a photographer has the option of acknowledging Depth of Focus and conducting a complete audit and adjustment of his equipment or simply ignoring it and using his camera gear as-is, assuming that the makers have dealt with the issue. Most seem to take the second approach and assume that their gear is properly adjusted and go forth to make pictures. Both approaches work but I can see that folks on either side who have from practical experience concluded that their way works might think that others who express a different view are nuts.

QT brought up the "good enough" concept. While I agree that "good enough" for professionals -can- be low it can also be quite high. Certainly for the bulk of pictures we see everyday, optical excellence requirements are very low compared to the near perfection needed to make huge enlargements. The point I make is that for paying work a good craftsman delivers work up to the standard called for or maybe just a bit higher. Using a 4x5 camera to photograph a small object that will be reproduced in a catalog at 3 inches wide is sorta like buying a Ferrari to make grocery runs. And of course sometimes "excellence" at performing a job is defined by something other than optical perfection.

A particular "look", high production rates and meeting deadlines are other possibilities (and not all) for judging "excellence" in photographic craft. To this point I have performed with "excellence" (in my mind) when the client needed all 106 shoes photographed with cmyk files delivered in one week - at three inches wide in the catalog they looked great and the job was on-time and on-budget. I have also performed with "excellence" by delivering a single image file for a large poster that took days to perfect. Neither performance made me a better person or proved me to be a great photographer. I really only did what the client wanted. So I might have been "good enough" or I might have been "excellent". Who can say?

So the question comes to "how good is good enough?" I'd guess that carrying a 35mm camera out in the world is not good enough for some folks on this forum. But for some things 35mm is the right tool for the job at hand and other times 4x5 might be just "good enough". When I, with no thought to Depth of Focus, use fine modern lenses on a properly aligned and adjusted view camera with film holders that hold the excellent modern film in the proper flat place, and then scan that film with a cheap flatbed scanner do I committ heresy? Certainly not if my goal is to make excellent 8x10 or 11x14 prints. I've proven that for myself and it is simply beyond arguement to me. Are drum scanners better than my flatbed? Of course they are, but my practical experience tells me that I am producing the desired result and the "betterness" of a drum scanner would be overkill.

In a way I think that a floppy old wooden field camera would be incapable of making a photograph of any perfection. (most of us know better from having seen with our own eyes) But how would it be possible if Depth of Focus is so critical? For that matter how is it possible to properly use the finest, tight, new monorail with a binocular viewer when I know that simply removing the heavy viewer produces some movement in the camera standards? I've just blown any chance I had at making a perfect picture! These two extremes clash and the heat generated is considerable.

There is no shame in either course, (or anywhere in-between) just go out and make the results you desire.

[Ted Harris]

Bill, Oren and Mark make an excellent point as it relates specifically to the use of roll film holders. Many users of older Graphic roll film holders, for example, are well aware of problems they can encounter as a result of improper tensioning/placement of the film in the holder. I understand it can be wholly or partially corrected but it is an issue nonetheless. I was the victem of this problem about 15 years ago when working with a Graflex XL system. The first test shots I took with the beast wre all 'softer' than they had any right to be or were partially soft in some places. I knew the rangefinder was right on and given the rigidity of the system knew it had to be related to the holders. I couldn't find anyone to fix them for me in a timely fashion and that coupled with the focusing nipple issue with that camera made me give the system up after only a few months of use. I go intothis detail simply because it can also be a problem with other roll holders as pointed out above. Usually you can solve the problem simplyby tensioning the roll before you close the back but not if the internal tolerences of the gears and rollers are sloppy.

I never thought of the problem in terms of Depth of Focus, and to this day don't tend to think of film flatness or gg placement issues in terms of Depthof Focus but they are, in reality, all a subset of this issue.

[Oren Grad]

A postscript to Ted's point, I was amazed to learn that there's no standard for the film-to-ground glass register for roll holders. Look at the table on this page:

medfmt.8k.com/mf/rollfilmback.html (http://medfmt.8k.com/mf/rollfilmback.html)

The difference between the extremes in that table (Linhof vs Wista) is a full 0.25mm. Maybe the manufacturers are intentionally building in a fudge factor reflecting their measurements of typical film bending with their respective film paths, but in the absence of a specific explanation backed up by empirical data this is pretty disconcerting.

[evan clarke]

On a camera to camera basis, it is surprising that the depth of film plane on the ground glass can be incorrect, inconsistent from corner to corner or both. I am a machinist and do a simple measurement with a depth guage to determine if the film plane of the ground glass is correct. All the other stuff is great, but if the film plane of the holder and the ground glass are not the same you are dead in the water..Evan Clarke

[steve simmons]

I am gong to take issue with Bill's post above.

I never made any statement about"anal photographers"

I did know about depth of focus, I said so in the suspended thread. I just questioned its day to day relevence. If you disagree fine.

Applying numbers to Cof C does not give a magical answer because the required size for a Cof C depnds on many variables. There are numbers considered acceptable but in a visual world they are not absolute.

Bill's post seems particularly directed at me and seems like an attempt to start a fight. He could have made his points, and they are his opinion and he is welcome to them, without going on and on about me. Despite what he says the required size of the CofC will vary depending on the circumstances (how much the image is enlarged, how closely it is looked at, etc, etc,).

Bill also questions the poll I took amoung working photographers. Since he was not sitting next to me whern I made the calls I am curious why he brought this up.

steve simmons

[Aaron van de Sande]

Henry, your comments are well articulated.. but may lack relavence for most (many?) of us here. Would I be going out on a limb by suggesting that the majority of people posting here are not professionals?
In other words, most people here are their own customers, and probably have no idea how large they may want to enlarge their negative. Many of us want, as far as quality is concerned, to have the best that is practically possible. To those of us shimming plate holders to work with film so we don't have to buy a 500$ film holder, depth of focus is important.

[Kirk Gittings]

Interesting series of threads on a subject that I knew virtually nothing about. I learned allot. Having said that.... will I do anything different than I have been doing since 1970?

[BrianShaw]

"we must ultimately arrive at some generalizations to guide us in the field"

Whoever said that... THANKS! I'm waiting, too.

I'm becoming convinced that I've wasted 15 years messing around in LF because I simply might not be smart enough to understand how to take a decent picture with one of these cameras. Maybe I should get on my knees and thank God that I actually like the images I take with a soft focus lens and Graphic Roll Film Holders. ;-) Is there any hope for people like me?

[neil poulsen]

I'm curious. What's a fix for a Graphic Roll Film Holder?

Here I go expressing my ignorance, but I use these and haven't noticed that much of a problem. In fact recently, someone who does only contact printing mistook one of my images as a contact print. It was and 8x10 from a 6x7 taken with a Graphic Roll Film Holder. (By the way, that's anecdotal and not data.)

[BrianShaw]

"What's a fix for a Graphic Roll Film Holder?"

It doesn't sound like you have much of a problem! Last year I had mine repaired by Fred Lustig (the return spring on the thumb winder broke). He seems to have done a really good repair/cleaning job. I doubt if he did any film plane or film flattness adjustments, however. He did seem to have replaced one of the film rollers for some reason. I never noticed a problem. I haven't used it yet (it's been a tough year) so I can't offer either test or anecdotal to make any further comment.

Oh... my apologies for anyone who is offended by the discussion of 120 film holders on the LF forum.

[Eric Biggerstaff]

Being the Non- Technical person I am, I was following this thread (sort of) until I got to Bill's post which left me completly confused.

I give up, I think I will never understand all of this.

But then, I was happily making pictures for years not knowing this so I guess I am no worse off. I am confortable with my results, so I guess I can leave the math to others.

It is a nice day in Devner, I think I will skip out of work and go make a photograph.

Have a great weekend everyone.

[Eric Biggerstaff]

Being the Non- Technical person I am, I was following this thread (sort of) until I got to Bill's post which left me completely confused( but it was an interesting read for sure).

I give up, I think I will never understand all of this.

But then, I was happily making pictures for years not knowing this so I guess I am no worse off. I am confortable with my results, so I guess I can leave the math to others.

It is a nice day in Devner, I think I will skip out of work and go make a photograph.

Have a great weekend everyone.

[BrianShaw]

Go for it Eric... make two photographs while you're at it.

Go for it Eric... make two photographs while you're at it.

;-)

;-)

[Eric Biggerstaff]

Sorry

Sorry

Hit button twice

Hit button twice

[Oren Grad]

Having said that.... will I do anything different than I have been doing since 1970?

Kirk, for my purposes the practical value of this sort of knowledge is primarily for troubleshooting - understanding the different failure modes of our tools and the circumstances under which they're likely to come into play is a big help in that respect.

For example, the likeliest source of weird focus problems when I'm working with my 4x5 wood-field is flex in the standards. On the other hand, with my 6x9 technical cameras, where the rear standard is absolutely rigid and I'll tend to be working at larger apertures, roll-holder film flatness and ground glass register are relatively more important.

I don't want to leave the impression that I need to be doing depth-of-focus calculations or fine tweaking of my equipment all the time just to get a usable negative - far from it. Most of the time I'm working at apertures and with subjects that are tolerant of quite a bit of slop. But sometimes things do go wrong, and when that happens it's nice to have a sort of mental checklist of different technical issues that might be involved, ranked in order of their likelihood as a cause.

[bglick]

Hi Steve

> I never made any statement about"anal photographers"

Your could be right, in that thread, you referred to them, as only the "most obsessed" photographers, then others, shortened your reference to the other term.... Sure glad you mentioned this, I feel much better.

> I did know about depth of focus, I said so in the suspended thread. I just questioned its day to day relevence. If you disagree fine.

When that thread comes back up, I think by reading it, it will become obvious to everyone, even by your own posts.



> Applying numbers to Cof C does not give a magical answer because the required size for a Cof C depnds on many variables.

Steve, from my post above..... Of course, the CoC can be effected more, or less, by lens MTF performance, aperture diffraction and depth of focus. The point being, Depth of Field alone, is rarely EVER the only determing factor of the CoC diam. This is NO small detail. It was me posting this to remind you of such, not sure why you feel compelled to then, re quote my post?????



> There are numbers considered acceptable but in a visual world they are not absolute.

This is my exact point, there is no absolute, in photography, most issues border on "acceptable" or "not acceptable" of the finished product. As several posters have pointed out here, there is many reasons why results can be....

acceptable, even with depth of focus shortcomings....

unacceptable, with NO depth of focus shortcomings.....

It's all based on what your trying to accomplish and the gear you're using. With the hodge podge of film holders and cameras in LF, it all can add up to potential problems. Hence why I take the opposite position as Steve does...... LF is the ONLY format whereas depth of focus should be of concern. And as Ted mentioned, it's all part and parcel of the final on-film resolution. It doesn't matter where the weak link in the chain is, it will surface on the film, so Steve, why dismiss depth of focus so quickly because you and your associates and 3 other books did not reference it? That reasoning still just doesn't make sense to me, that's one of the many things that baffle me, specially being an author on technical books in this field? I keep trying to understand you Steve.

> Bill's post seems particularly directed at me and seems like an attempt to start a fight. He could have made his points, and they are his opinion and he is welcome to them, without going on and on about me.

I was responding your YOUR post Steve, of course I was directing it at you. Just so its clear, I have zero desire to pick a fight with anyone in the real world or in a forum, specially you. I don't have the energy to withstand your persistence to "never be wrong", and you can be assured I too will fall victim as others have who challenge your statements. They get burnt out, trying to convince you 2+2 = 4, so they eventually move on. But, I hope these brave posters have helped other fellow photographers along the way, as I have sure benefited from many of them through the years on this forum.

In all fairness Steve, I spent more time trying to give credit to other posters on the suspended thread who relentlessly tried to help you in a nice professional manner before you went on the defensive. I personaly hope we don't loose these posters, due to the frustration level they experienced in the suspended post, as I did not notice their participation on this post. If anything, I like to think of my role in this and the suspended post, as a "forum medic", risking my life, running through war zones, saving the casualties in threads you particpate in. But you will be happy to know, my "term of duty" is up soon, so you can relax :-) BTW, I never attacked your books or magazine one bit, I only comment what you write on this forum, and isn't that the purpose of the forum? In the suspended thread, I did it as peaceful as possible, I will continue with this approach Steve. And it's OK you failed to comment on the "meat" of my post, I fully expected this, as you have trained me well in the suspended post. But I must admit, I was shocked when you did not defend yourself when Oren pointed out that your OWN magazine did an article on this subject in 1996 and concluded this was an issue LF users should be aware of. I respect your silence.....

> Despite what he says the required size of the CofC will vary depending on the circumstances (how much the image is enlarged, how closely it is looked at, etc, etc,).

Steve, please, you need to re-read my post, it was ME bringing this to your attention, not sure why you are tyring to turn-the-tables here...and I will not waste bandwidth constantly re pasting my own posts.

> Bill also questions the poll I took amoung working photographers. Since he was not sitting next to me whern I made the calls I am curious why he brought this up.

I only commented on your reasoning of why depth of focus should be dismissed, and then your conclusion, "relax, let's go photograph." It was the same poll, and the same books you quoted in the suspended thread. The key is here, you never commented on the meat of the subject matter and the discrpancies many posters have above, with your first post here. You find the issues irrelevant. Instead, you operate under the premise, if you can't beat the message, beat-up the messenger! Make sense? Same "mode of operation" in the suspended thread. Anyway Steve, I do wish your books and magazine success, as the LF community needs such. I think it's obvious your products would benefit by treating everyone with respect and fairness on this forum, as this forum probably respresents the largest customer base for your producuts, right? It's hard to beleive I have to "state the obvious", but, such is the case.....

Eric...... >Being the Non- Technical person I am, I was following this thread (sort of) until I got to Bill's post which left me completly confused.

I am sorry for such..... and I certainly don't suggest everyone to get burried deep into these issues as I mentioned in the suspended post, photography has everything from artist to scientist (and everything in between) participating. Let this post serve as a "heads up" of things that can happen.

If you're not happy with your current results, do some very simple tests, such as photographying a flat wall (but not too close 40ft+) Take a few shots, one focussed one right on the wall, one slightly beind the wall, and one slightly in front of the wall. Use the widest f stop lens you have, shoot at 4.0 or f5.6, this will exaggerate any problems. Be sure to put a label on the wall, (1,2,3, etc.) so you dont' confuse the chromes. Use the same technique you normally use to focus, use the film holders in question, or test them all, and once again, mark the scene accordingly. View the film on a light box and be sure the chromes which were focussed correctly, are the sharpest.

If you pass this test with flying colors and normally shoot at f16+, your technique and photo gear is completely void of all these issues. If you notice different results, well, based on how concerned you are, you can go to the next level. You can also try to shoot an open area, with signs posted at different distances from the focus point.... just use some text that comes out of your office printer.....this will save on film cost, as you always focus at the ONE sign (target) in the middle. Be sure to put min. 5 targets total at varying distances, as if the alignment is off, you can tell in which direction and how far. Again, this is a rough-cut test. But it demonstrates how complex issues can be reduced to simple tests to either confirm no problem exist, or maybe discover an alignment issue.



Oren, THANK YOU very much for your roll film holder contribution! I had problems with this in the past and never wanted to spend the time to investigate it, as I felt it was easier to simply buy Toyo roll film holders as I use all Toyo LF gear. This immediately corrected the alignment issues. It was cheaper then doing extensive testing and mechanical corrections. This is one of the benefits of trying to stay with one maker for all your gear. Of course, not too probable for most.

The .25mm you quote above, demonstrates just how radical the introduction of one piece of gear can toss the alignment issue into anarchy. My post mentioned the .3mm margin of error the depth of focus has at f16 for "all" issues, whereas in this case, just using the "wrong" roll film holder can account for all the depth of focus allowance, leaving nothing available for other mis alignment in the view camera system. In my opinion, this is one of the many reasons it's risky business switching from MF cameras to view cameras with RFB's of similar format size. Yes, you gain movements, but sometimes at the expense of many other negative issues. Of course, with prudence and testing, much of this can be avoided or corrected.

Oren, also your previous posts completely sums up how I feel about this entire issue. It's a trouble shooting tool, and a useful set of knowledge to 1) avoid buying gear that might create the alignment problem or 2) knowing what to look for to see if the problem existed. Again, thank you for the contribution.

[Kirk Keyes]

To see if any of my photo books had anything to say on about depth of focus, the first one I reached for was my copy of "View Camera Technique", by Stroebel, 6th Ed. On pages 138-9, it lists the 4 significant relationships that I think Steve recounted at the start of this thread. In closing the section, I think Stroebel makes the best arguement for caring about depth of focus:

"If a subject exactly fills the depth of field space, then there is only one position the film can occupy, and there is no tolerance remaining for the photographer or the camera."

I would like to tie this into what the other Kirk wrote: " Having said that.... will I do anything different than I have been doing since 1970?"

Maybe not for you... But for me, what Stroebel stated had a big affect on my choice of camera.

When I started, I took the route of using a lightweight 4x5 camera, a Nagaoka. It was nice and light at a bit over 3 pounds, and pretty compact. But I kept noticing that it flexed all over the place - putting the dark cloth one, placing the loupe on the gg to focus, placing the film holder in...

Now I knew that the flexing, when compared to the depth of field, really had no affect on anything. But then compared to the depth of focus, it was a huge amount of movement. And I lost several shots because the camera was just not rigid enough to place a loupe on the ground glass and not have it move. Having used a Linhof Tech IV for a while earlier, I decided to ditch the Nagaoka and get a Technika.

Now I don't mean to badmouth wood field cameras, as I'm sure many of them are much more rigid than the good old lightweight Nagaoka was, but I have the comfort of knowing that I can shoot without having to take actions to insure that the film will end up acceptably close to the plane of focus.

Kirk, I think that at this point, you probably do not have to take depth of focus into consideration on a daily basis as your camera kit is most certainly pretty well tested by now. But for others, that are getting both new or possibly old or poorly adjusted or poorly functioning equipement, remembering and understanding the principle of depth of focus and Stroebel's summation of it may someday be useful.

Kirk - www.keyesphoto.com

PS - Mark, glad you enjoyed the photos on the web site, and I'm planning on getting more B&W work up there some day soon...

[Kirk Gittings]

Kirk understood.
Kirk

[Kerry L. Thalmann]

Wow, between this thread and the suspended one there has been a LOT of heat generated and even some light shed on the topic of depth of focus. There also seems to be some sort of technician vs. artist debate brewing. This would seem to imply that one has to make a choice between the technical and artistic aspects of photography and that the two are mutually exclusive. I strongly disagree (not with anyone in particular, just with this premise in general) and believe it is possible, even desirable (but not required) to be both an artist and a technician. Ansel Adams used the technical understanding of his materials and processes to produce beautiful photographs. Edward Weston used a much less technical approach to also produce beautiful photographs. The important thing is they both chose the approach that worked for them and even though they chose different methods, there is no documented evidence that they ever called each other names or publicly denigrated the work of the other. In fact, they were close friends who respected and admired each other's work. We should all learn from their example and learn to not just tolerate each other's opinions, but to welcome them and embrace them (OK everyone, let's all join hands around the campfire and sing Kum Ba Yah).

On the subject of depth of focus... Although I am a technical person by training, I always look for a simple solution to any problem. In my simple-minded approach, this entire issue can be summed up in one equally simple-minded sentence:

It's only a problem when it's a problem.

I consider depth of focus issues to fall into the same category as things like light leaks. You can go years, even a lifetime if you are lucky, without ever seeing any evidence of a problem. If that's the case, as others have recommended, forget about it and keep making photographs. Until you actually notice a problem, whether it's a light leak or a depth of focus issue, there is nothing to fix. So, why worry about it. If you do experience a light leak (or a depth of focus problem), then it's time to take action, determine the cause of the problem and implement a solution. As with light leaks, there are some very simple tests that can be used to check for depth of focus problems. With light leaks, you can check your bellows for pin holes, check that your film holders are light tight, etc. With depth of focus issues check the alignment and registration of your ground glass, check for warped or out-of spec, film holders, etc. The point is to diagnose the problem, identify the source and fix it. Then get back to making photographs and living a happy and productive life. No point in arguing about it. Unless you share a camera and film holders with someone else on this forum, whether or not you experience a depth of focus problem is specific to you and your equipment.

Of course, there are specific applications and circumstances where depth of focus problems are more likely to be noticed, but again sweeping generations should be avoided. There are just too many variables to assume somebody else will or won't have a depth of focus problem.

So, it is certainly possible to spend your entire life making beautiful photographs without ever encountering even a hint of a depth of focus problem. On the other hand, it is equally possible for a great artist's vision to be thwarted by a camera with an improperly registered ground glass or out-of-spec film holders.

Sorry if my comments seem to re-state the obvious and repeat what others have said with more vigor and passion. I'm just finding the aggressive intolerance and lack of respect for other's differing (but no less valid) opinions a bit tiresome. There's room here for a whole wide range of opinions and this is one of those issues where both you and the guy you are so desperately trying to prove wrong could both actually be "right".

Kerry

[William Mortensen]

While Bill's above-recommended method of shooting several chromes of a flat wall (I'd shoot paper negatives for this myself) might be more accurate, I check my focal plane registration as follows: take the back off the camera, lay a rigid straight edge across the inside of the back and measurefrom the straight edge to the gg center and four corners. Then put in a filmholder with a crappy old negative in it (no dark slide) and make the same measurements. This seems as accurate as one could make the measurements, (I used a digital calliper). Anybody see any problems with this method?

I use Fidelity and Lisco holders, and checked one of each in each of the three 8x10's I use. No problems found, and I've never had any depth of focus issues with my negatives. As Oren noted, this is probably mostly a trouble-shooting issue, and I suspect it will never arise for most photographers. Then again, I hope to finish building a ULF and a film-holder or two this summer, and it will be *THE* critical measurement.

[bglick]

Kerry.....

> There's room here for a whole wide range of opinions and this is one of those issues where both you and the guy you are so desperately trying to prove wrong could both actually be "right".

Those who know me, since 98 on this forum, I have never been one whose goal it is to
"prove people wrong." This was a rare case of a suspended thread being "continued" for the sake of re affirming a position many posters rightfully challenged in the suspended post.

When I think back to many historical posts on this forum looking for information, I recall often someone challenging a position, or possibly even making a very vague refernce more clear and give it some legs. This is what happened in the suspended thread, an inaccurate and vague postion, and now the same in this thread. I applaud those who stood up in the last suspended thread. But, yes, I marvel how I got suckered into this myself, but, when I look back at the posters threads, I now realize I am not the only one who "took the bait." In the end, I hoped some people benefited from the information, if not, I will clearly avoid such in the future, as other posters have done. I apologize to anyone who found my post the least bit unfair in any way.

As for light leaks vs. alignment issues...... in my opinion, a weak comparison, as light leaks represent a system break down, and are "usually" obvious on film. Alignment issues are impossible to see, can come and go based on using different film backs, can appear only when shooting flat subjects, but not as objectionable shooting near/far subjects, etc. Quite a tricky variable. It's not always noticeable if your not pushing enlargement factor, etc. Then when you notice soft chromes, was it your focus, was it camera shake, was it subject movement, etc. etc. etc. Much easier in my opinion to know your gear well. As I mentioned many times in this post and the supsended post, this is not everyones cup of tea, many prefer to just wing it, and when a problem surfaces they consult a camera repair technician. Of course as with most issues, if one never experienced the problem, they have a hard time relating how others can experience it.

[Henry Ambrose]

Aaron,

I answered QT's "good enough" post because it does have something to do with Depth of Focus in that Depth of Focus is a range of acceptability just like all photo work is, whether commercial or private.

What Evan Clarke wrote is most all the answer - the film plane and the ground glass must agree, all that's left is to focus the camera and expose the film without disturbing your setting. "Perfectly" would be great but within tolerance gets the job done. There is only one perfect film/image plane junction, anything else is to a tolerance of acceptability (or not). I suspect that Kodak has some lab equipment that can tell when the focus plane is precisely in a particular layer of the film emulsion - now that is real precision - but we will never approach that level of precision and don't need to do so. Most standard film holders will hold the film in the right place when all is right with the world and the holders and camera back are to specification. You'll get "good enough" results, which might be "quite good" or "sorta good" maybe even "excellent" -- if the print you make is what you wanted, you did it "good enough".

Depth of Focus is a description of a natural or optical phenomenon that you really can't do anything about other than to be sure your film gets exposed within the range of acceptable Depth of Focus for your printing requirements. In less words, if your gear is all correct in its dimensions and functions and you have focused properly, Depth of Focus is still there and you are operating within it. So when you are shimming your plate holders for film use (or whatever thing it is you are measuring or adjusting) follow Evan's advice and you should be ready to make pictures.

[Kerry L. Thalmann]

Bill,

Those who know me, since 98 on this forum, I have never been one whose goal it is to "prove people wrong." This was a rare case of a suspended thread being "continued" for the sake of re affirming a position many posters rightfully challenged in the suspended post.

My comment was not directed at you, or anyone in particular. It was just my general impression as to why the previous thread (and now this one) went on and on well after everyone had made their points about the subject. Again, this is not directed at you (or any particular individual), but at some point all the useful information has been shared and people are just repeating their message with different words, or worse still, getting off-topic and personal.

As for light leaks vs. alignment issues...... in my opinion, a weak comparison, as light leaks represent a system break down, and are "usually" obvious on film. Alignment issues are impossible to see, can come and go based on using different film backs, can appear only when shooting flat subjects, but not as objectionable shooting near/far subjects, etc. Quite a tricky variable. It's not always noticeable if your not pushing enlargement factor, etc.

That was a deliberate oversimplification on my part. My whole point is if you can't see a problem on your final output, then no problem exists. It's the old "if it ain't broke, don't fix it" cliche. Yes, alignment errors can be harder to detect and diagnose than light leaks. That was not my point (my fault for not expressing myself better). If there is a problem (or if someone just wants to make sure their gear is up to snuff), it can be checked with a few simple tests and/or measurements. On the other hand, if someone is getting acceptably sharp results at their maximum enlargement size, do they really need to spend time running these tests and worrying about their ground glass alignment and registration? Of course, "acceptably sharp" is a subjective term - but that's part of the point, everybody has different standards (as well as different equipment).

Much easier in my opinion to know your gear well. As I mentioned many times in this post and the supsended post, this is not everyones cup of tea, many prefer to just wing it, and when a problem surfaces they consult a camera repair technician. Of course as with most issues, if one never experienced the problem, they have a hard time relating how others can experience it.

I'm all for people knowing their equipment. I admit I'm a bit anal retentive when it comes to my camera gear. I try to identify and eliminate anything in the chain that would impair my ability to make the kind of photographs I desire. Then I can't blame anything or anyone, but myself for my poor results. That then allows me concentrate on improving my abilities and not worry about the equipment being a limiting factor (at this point, I am quite confident it is not my gear that limits the quality of my photography). I recently sold some 40"x50" prints (made from 4x5 chromes). The client was absolutely thrilled with the sharpness and detail in the final prints, and I admit I was pretty happy with the way they turned out, too. I have no plans to make anything bigger than a 10x enlargement from my 4x5 chromes (and I don't even go that big very often). So, I'm confident my equipment is up to the task and not a limiting factor.

For the record, I have had holders that were out of spec. I threw them in the trash and went back to shooting. I also once had a camera with a mis-registered ground glass. I installed some shims to correctly position the ground glass, re-tested and went back to shooting.

Ultimately, I consider myself an agnostic in this whole technical vs. artistic debate. I'm a technical person by training. So, technical concepts that may seem simple to me may confuse others with a less technical background. That doesn't make me a better photographer than them, but I do believe the technical knowledge I have aquired has helped improve certain aspects of my photography. However, as I type this, hanging on the wall above my monitor is one of the best photos I've ever made - way back when I was new to large format, was using a "sub-standard" camera and lens and lacked the technical understanding I have acquired in the 16 years since (and still looks great at 20"x24"). So, I can see both sides of this issue. Yes, it helps to know your gear (and your materials) like the back of your hand (and I do), but it is not always necessary. To each his own.

Kerry

[Kerry L. Thalmann]

P.S. I apologize to Bill, and others, if my two posts above are a bit rambling. I jumped into this thread late and did not participate in the original. I think I managed to wade through most of the original thread before it was removed, but now that it's gone it's a bit hard to remember EXACTLY who said what. I have a good general recollection of what was said, but avoided mentioning anyone by name unless I am responding directly to something they have posted here in this version of the thread.

Kerry

[bglick]

Kerry, no apologies required...... you have always been a generous, polite and knowledgeable contributor to the entire LF community. I applaud and appreciate your generosity to the LF community. Although I did not take your post as criticism towards me, I would accept criticism from you with open mind and open arms! Glad to hear you sold some nice large prints, your work is first rate.

After tweaking my system through the years, I too have made many large prints, sometimes pushing 4x5 to 60" with excellent results. However, it took me some time till I found the right lenses, right DOF or lens tilt scenes, well tuned gear, scanners, etc. till I could push enlargements this far and acheive tack sharp prints..... ..and even then, many shots can't be pushed this far..... again, all part n parcel of on-film resolution which is what this post addressed. Hence why I will never surrender my 8x10 camera...horses for courses!

[Jerry Fusselman]

Kerry writes, "My whole point is if you can't see a problem on your final output, then no problem exists. " And also, "It's only a problem when it's a problem."

These sound self-evidently true, but I think not. Of course, no problem = no problem, but that's not really what he is saying. I understand his point to be that if you cannot see a problem, then there is no problem, and that is clearly false. There can be problems you cannot see until it is way too late.

The heuristic principle that all problems are immediately visible is not really correct. Maybe exactly one of your film holders is off by enough that a 10x enlargement will be a big disappointment, but you will find out only after a delay of several years.

In art, there is always a possibility that you could do something better, and occasionally, that something is a technical detail such as making sure your ground glass is well calibrated to all of your film holders or learning how to balance diffraction with depth of field.

[Kerry L. Thalmann]

The heuristic principle that all problems are immediately visible is not really correct.

Jerry,

I never said the problem would be immediately visible. In fact it can't be in this case. The soonest you could see a depth of focus issue is after the film is processed. You could take measurement to check alignment and registration, but there will be no visible evidence of a problem until you shoot some film - and even then you may not detect the problem. Which is why I wrote:

"My whole point is if you can't see a problem on your final output, then no problem exists."

Maybe exactly one of your film holders is off by enough that a 10x enlargement will be a big disappointment, but you will find out only after a delay of several years.

This is one reason I habitually check the sharpness of my chromes with a loupe when I get them back from the lab. If I'm not getting consistantly sharp results, I know there is a problem and I have a pretty good idea where to start looking (careful note taking helps).

I'm not suggesting people shouldn't test their equipment or understand the variables that effect image sharpness. I think we're actually on the same page here. I know my equipment well enough, through both testing and years of actual use, to trust it. If I get a new piece of equipment, I don't totally trust it until have convinced myself it will perform as expected. Depending on the type of equipment, that may mean some controlled testing is in order, or it may mean just shooting a few sheets of film and checking the results with a loupe (which I do anyway as force of habit). Testing is one way to quickly get to know your equipment, determine its limitations and identify any problems. Actually using your equipment to make photographs is another way to get to know it. It may not be as efficient as testing, but some people may find it enjoyable. Both approaches are valid, and I personally rely on both. I don't see why this has to be an either/or issue. I have done a lot of testing of my equipment, but sometimes when I get a new lens or other piece of gear, I just can't wait to get out and make some photographs with it. I've made some of my best (IMHO) images with new gear that I failed to test prior to using it. Like a kid at Christmas, when I get a new toy I can't wait to start playing with it. Of course, if that new toy doesn't perform as expected, I will revert back to testing to figure out why.

On the other hand, there are times when testing up front is most prudent and can nip any potential problems in the bud. I'm currently assembling a 7x17 camera. I don't trust woodworking skills enough to make the camera back. So, I will have it made for me by someone with more experience and better skills. I have already acquired two 7x17 holders (thanks Chris) and will send them out to have the back made to match. The first thing I'll do when I get receive the back is perform some tests to verify the registration and alignment of the back and both holders. If I get any more holders, I will also immediately test them. The back and the holders are all hand made, and by different individuals. So, there is an increased potential for error. Now, if I was buying a new 4x5 ARCA-SWISS or some other precision machined metal camera I'd be much less concerned about problems with the back being out of spec.

Kerry

[Kerry L. Thalmann]

Bill,

Thanks for the kind words. I wasn't fishing for compliments, but I'll take 'em when I can get 'em.

Glad to hear you sold some nice large prints, your work is first rate.

Thanks. Every couple years I manage to land a project providing prints to an office or public building. This particular job is a new medical clinic. They are displaying three of my 40x50 prints in the lobby/waiting room. They may also be buying some 20x24s and 24x30s for some of the offices and exam rooms (fingers crossed). I also supplied several prints (smaller in size) to the (then new) federal courthouse here in Portland a few years ago. I hadn't been back until this past April when I got called to serve jury duty on a federal case. It was fun to see my work on display in such a beautiful building. A couple weeks later, my kids visited the courthouse on a field trip. So, they also got to see my work on display (which they thought was cool).

For my own personal use, I rarely print larger than 20x24. 16x10 and even 11x14 are common (I only have so much wall space). But it's nice to know the work holds up when enlarged 8 or 10x. I also sell a few prints through a gallery and the smallest size they want is 20x24 and hey prefer 24x30 or 30x40 (they also sell a lot of artwork to businesses to display in their public areas).

However, it took me some time till I found the right lenses, right DOF or lens tilt scenes, well tuned gear, scanners, etc.

Yep, been there, done that. I'm very satisified with the quality of my gear at this point. I'm still not totally up to snuff on scanners. When I need something made really big, I have it drum scanned. It adds cost, but they only time I need anything made big enough to require a drum scan, it's for a paying job. So, I can justify the expense.

Kerry

[Jerry Fusselman]

Kerry,

Well, when I wrote immediately I meant it in
the context of the time frame mentioned in the next
sentence---i.e., several years. I am not
quite foolish enough to suggest a time frame of a few
seconds after exposure. My immediately allows
for the time needed to look at the developed film with a
loupe.

But I do not think that looking with a loupe will uncover every problem.
I think you would agree, because you wrote, I recently
sold some 40"x50" prints (made from 4x5 chromes)....I admit I was
pretty happy with the way they turned out, too. If your
undoubtedly very close inspection with a loupe had removed every possible worry that
you might have had about the quality of the chrome, then you would not have
been so happy with the way they turned out---there would have been no surprise
at all.

The point I have been trying to make, alas maybe not clearly enough, is that a good
and experienced large-format photographer may have some depth-of-focus problems
without knowing it. His work could maybe be better, even though he regularly
examines his work with a loupe.

I would not dream of criticizing your techniques; it was only two of your sentences that I thought
could easily be misinterpreted into something you had not intended. You said,
"if you can't see a problem on your final
output, then no problem exists." and "It's only a problem
when it's a problem." These sentences sound anti-testing and anti-understanding to me.

Anyway, you subsequently made
clear that photographers should ``test their equipment [and] understand
the variables that effect image sharpness.'' And I agree. By testing, I am sure you
mean to include careful examinations of shots you wanted to take anyway.

Remember, the context of this discussion comes from the original thread
(Image quality: Normal holders vs. Quickload), which
contained this exchange:

Writer A said this:

My advice is to look for consistency in your working methods.
Consistency of film plane is important ... Part of that consistency should be a
consistent film plane depth so switching to and fro from quickloads and
normal film holders will likely give a different film plane depth. i.e. if
you are going to be using normal film holders then use all of the same
make and vintage and check their depth and set your ground glass to
correct depth for those film holders....

Writer B said this in response:

This is completly unnecessary. Film holders, of all types, have been shown
to be satisfactory for years and years, and years. There will be the
occasional bad apple but it is not related to the MFG or style. Show me a
pro who makes his/her living practicing this type of obsessional behavior.
They know better and don;t have time. It is not necessary. ... Your commentt
[does] nothing to clarify the question or help him
understand what large format photography is all about.

Seems to me that your position, Kerry, is closer to A's advice, even though the
two sentences I took issue with seem to me to support B's position. I could try
to summarize my overall position as follows: Even if most of your images usually
look pretty good under a loupe, you might be able to improve your results by
checking your film-plane and ground glass alignments.

By the way, Kerry, when are you going to write a book for us? I would be one the first
waiting in line to buy it.