stopping down for focus

[Los]

so, stopping down for focus (depth of field) seems like a pretty popular technique. so i tried it. using some aperture recommendations for numerous focus spreads. and it worked, sort of. while the near and far points are in focus, they have a fuzziness around the edges. i'm guessing diffraction is the cause of this. so my questions are:

Does anyone else see this phenomenon in their own deep stop photos, and are there any ways of improving it (unsharpmask, contrast, focusing somewhere other than halfway between the focus spread)?

[C. D. Keth]

Well, you don't focus halfway between. It's generally a third of the way from the closest to the farthest. The split gets closer to half and half as you get closer to the lens.

That doesn't sound right to me. It sounds like you lens either has some aberrations that are going wonky or you're estimating the spread wrong.

[David Karp]

Well, you don't focus halfway between. . . .

Actually, you do. Check this out: http://www.largeformatphotography.info/fstop.html.

And this article mentioned in the aformentioned page: http://www.englander-workshops.com/documents/depth.pdf

[Brian Ellis]

I can't really envision the effect you're getting. Fuzziness around only the areas that are "in focus" doesn't sound like diffraction since diffraction shows up as a slight softness of the entire image, not just parts of it. Diffraction is a potential problem with smaller formats, especially 35mm, because of the big enlargement factors involved (e.g. roughly 8x for an 8x10 print from 35mm film, which translates to a 32x40 print for 4x5 film). But it isn't usually a realistic problem with 4x5 and larger film because of the relatively small enlargement factors normally involved.

I assume you're using the focusing technique described in the first article David cited. If you're using that technique correctly any "fuzziness around the edges" is almost certainly the result of something other than diffraction but without knowing more details it's hard to figure out what that might be. In addition to providing more details (e.g. are you looking at a print or a negative, what film format are you using, is this b&w or color film, exactly what focusing method are you using) it would also help if you could post a copy of whatever you're looking at or at least a more detailed description of one of the images and the effect you're seeing).

[JPlomley]

I worry a bit about focus shift in the corners with wide angles, so if the light allows, I will determine focus spread with the lens stopped down to f/8 (even though maximum aperture is f/4.5) and use a Silvestri loupe instead of my Schneider (Silvestri does a better job at getting to the corners on my Arca Swiss GG and has a magnification of 6x which is beneficial for wide angle lenses). With all my other lenses I determine focus spread with the lens wide open, set the focus point to the median, and have never had a problem. Have never noticed any "fuzziness" when I stop down for the purpose of positioning a GND.

[Leonard Evens]

It is hard to respond because we don't know how you are choosing the f-stop. If you are using any plausible method to determine the f-stop, the image should be sharp at the limits of DOF over the entire image, provided you are viewing the image at a reasonable distance. Of course, almost any lens will perform better in the center than at the edges. Lens aberrations and curvature of field will generally degrade performace as you leave the center of the image circle. This will be clear if you view the image under significant magnification. So if you are using a loupe to look at the image, you should expect what you see. The basic method for choosing the f-stop based on focus spread, considering just defocus and ignoring diffraction, assumes some specification of sharpness in terms of a chosen maximum circle of confusion (coc). That in turn assumes the image is being viewed in a certain way. Usually you are advised also to stop down one or more additional stops to take account of less than perfect lens performance. If you use high magnification to examine the image, you are in effect choosing a very small coc, and lens defects are bound to play a significant role. Also, diffraction will be important even at moderate apertures. If you use Hansma's method, you will get, in principle, the best you can expect balancing defocus and diffraction. But, again, if you magnify the image enough, you will detect degradation of the image due to field curvature and other factors.

The proper placement of the standard is the harmonic mean of the lens to film distances for the near and far points. But in almost all practical situations this is very close to the midpoint between the two positions, and you should use that, unless you have some reason to favor either the foreground or the background. Some people have argued that you should always favor the background, but I don't find such arguments convincing. There are various one third rules, but they are generally wrong except in limited cirucstances.

[steve simmons]

The method I teach, and it worked in my recent Monterey workshop, is to have the student focus so that the closest objuct of interest and the farthest object of interest are equally out of focus. Then, as they close down, the dof lines spread equally near and far so that these two objects are brought into the dof area at the same f-stop. This is after all best efforts with movements are done.

One of the mantras I teach is "The groundglass is truth." If you really learn to study and look at the gg you won't be fooled.

steve simmons

[Robert Fisher]

Steve, what is "plan B" when the GG goes dark after stopping down?

[jetcode]

Steve, what is "plan B" when the GG goes dark after stopping down?

particularly in a situation such as a macro shot where the bellows extension just took 2 stops of light and when you stop down to f/16 you can barely see the image let alone guage it's sharpness

[steve simmons]

Have a big darkcloth that really blocks the light, use a 4x loupe, stay under the cloth to let your eyes adjust. The students actually found this to be surprisingly easy.

In the case of closeup work you can do a check with Polaroid. Type 55, where you check the neg, can be a useful tool. Outdoors, in daylight, no one had a problem.

I am also a fan of the gg brighteners as most of them will brighten the image by 2 stops.


steve

[JPlomley]

How practical is Joe Englanders suggestion for biasing infinity focus when no movements are involved? For example, let's imagine you have a 2mm focus spread. We would setthe focus point either 1/3 back from infinity or 2/3 forward from close-focus in order to bias focus for infinity (focussing with the reard standard). Putting this into real measureable numbers on an Arca Swiss monorail, this is pretty tough since increments are in 1mm. So 2/3 forward from close focus for a 2 mm spread would be 1.3mm. My rail is just not this accurate. So I question the practicality of the technique. Would it not be more practical to use the grids on the groundglass?

[Paul Metcalf]

Actually, you do. Check this out: http://www.largeformatphotography.info/fstop.html.

And this article mentioned in the aformentioned page: http://www.englander-workshops.com/documents/depth.pdf
1/2 way in image space, that's theoretically correct. And that corresponds to approximately 1/3 in scene space for non-high magnification situations.

[Vaughn]

The method I teach, and it worked in my recent Monterey workshop, is to have the student focus so that the closest objuct of interest and the farthest object of interest are equally out of focus. Then, as they close down, the dof lines spread equally near and far so that these two objects are brought into the dof area at the same f-stop. This is after all best efforts with movements are done.

One of the mantras I teach is "The groundglass is truth." If you really learn to study and look at the gg you won't be fooled.

steve simmons

Pretty much what I tell our students...especially the last bit. Since judging if the close and far objects are "equally" out of focus can be difficult, I tell them to close down the lens and see if the close and far come into focus at the same time. If, for example, the far comes into focus first, then refocus a little closer and try again.

I also suggest that once they find an fstop where everything is in focus, to close down one more fstop, since the lens is probably sharper than one's eyes.

I like this practical WYSIWYG approach for beginners. Then if they are interested, they can explore other methodology.

Vaughn

[Los]

thank you everyone for your help. as brian suggested, the "fuzziness" is over the entire image. i usually shoot at apertures between f8 and f16 on fuji 160s. i had an 8x10 made from a flatbed scan, but i'm basing my observations from viewing the negative on a light table with a toyo groundglass loupe. the largest i intend to print in 20x24. here are my notes from the test:

135mm
f45.3 @ 1/8th sec
w/ polarizer
focus spread 4mm
recommended stop f32.6
focus is from the foreground white fence to facade of house across the street.

the picture attached if from a 600dpi scan at full size, cropped, and unsharpened. given the softness of the flatbed scan, i think you can still see where the details on the suv (about center on the focus spread) are much sharper than the fence in the foreground.

i am wondering if this can be made to "appear" sharper by plus development, scanning and USMing. or am i print sniffing at this point?

http://home.mindspring.com/~carlosjackson/sitebuildercontent/sitebuilderpictures/dof_unsharp_crop.jpg

[steve simmons]

You have way too many variables here.

1. this is a print from a scan. How good is the scan?

2. Why are you shooting at f8-16. LF lenses are generally, and this is an over generalization, better in the 16-45 range.

The problem may or not be the lens and/or the negative.

Your problem could be dof. What do you nean when you say the focus spread is 4mm???

Before you can get any helpful advice you need to go back to the basics and stop combining apples and bananas.

steve simmons

[Los]

You have way too many variables here.

1. this is a print from a scan. How good is the scan?

you're seeing the scan from the neg. not a consideration. a quick a dirty proof.

2. Why are you shooting at f8-16. LF lenses are generally, and this is an over generalization, better in the 16-45 range.

i like resolution and sharpness, both are better wider on the stop. dof is the tradeoff.

The problem may or not be the lens and/or the negative.

never said there was a problem. systems' fine. just trying to adjust one aspect to my liking.

Your problem could be dof. What do you nean when you say the focus spread is 4mm???

my micro focusing bed has a scale in mm. near focus at -4mm, far focus at 0. spread 4mm.

Before you can get any helpful advice you need to go back to the basics and stop combining apples and bananas.

i'll have you know, it was apples and grapes!

steve simmons

[Brian Ellis]

I can answer one of your questions. Plus development affects contrast, it won't affect apparent "sharpness."

In response to Steve's question of why you were shooting at f8-f16, you said "I like resolution and sharpness, both are better wider on the stop. dof is the tradeoff."

There are a couple misconceptions reflected in this response but the main one is your apparent thought that it's better to have good "resolution and sharpness" than adequate depth of field. I assume, in view of your original question, that you're thinking the effects of diffraction will adversely affect the "sharpness" of the photograph if you stop down below f8-f16. If that's the case then in my opinion your thinking is wrong. The effects of inadequate depth of field will almost always be far more apparent than the effects of diffraction when using 4x5 or larger film and making an enlargement in the 4x-5x range. In general, it's much better to have the depth of field you need to make the photograph you want to make than it is to worry about diffraction when using 4x5 and larger film.

Unfortunately I can't really figure out what's going on from the image you posted. On my monitor the entire image looks fuzzy. In other words, it looks like you didn't get anything in focus. If that's how it really looks then you just aren't focusing your camera properly. A very good place to learn how to focus a LF camera is the first article that David cited in his response to your original question. Steve Simmons' method will certainly work too but I'm not sure it's the best method for a beginner because I think it takes some experience to be able to tell by looking at the ground glass when two things are equally out of focus. But you could give it a try if you like and see if it works for you.

[domenico Foschi]

What Kind of lens were you using?
It seems to me that there is a lot of perspective compression in the image as if you used a tele lens.

[David Millard]

To me, it looks like the overall blur may have as easily resulted from camera shake due to an unstable tripod/head, apart from any optical issues from your lens.

[Dick Hilker]

Steve, you mentioned, "I am also a fan of the gg brighteners as most of them will brighten the image by 2 stops."

I tried to find some info about this, but came up with nothing: what do you suggest?

[Leonard Evens]

You say "'I'm basing my observations from viewing the negative on a light table with a toyo groundglass loupe". As I noted previously, if you view any image under high magnification, it is going to look somewhat fuzzy. But a magnification of 2-4 times might be just about right to simulate viewing a 20 x 25 in print.

You say that " the picture attached is from a 600dpi scan at full size, cropped, and unsharpened."

What do you mean by cropped? How much of the full size frame are you showing? If it is a relatively small portion of the frame, then my above remark might be relevant, since that is equivalent to looking at the image under high magnfication. This would be particularly true with a 600 ppi scan.

However, let's assume that the picture shows close to the full frame and the scan reflects what you see when looking at the negative on a light table with at most a 4 X loupe. At f/45 1/8, as David pointed out, camera shake could easily blur everything. Also, it appears that the fence in the foreground is sharper than the background, which suggests that you were focusing at the fence or even in possibly front of it. But that could be an illusion based on its contrast with the background.

Assuming you used focused halfway on the rail between the near point and the far point and that something in the range looked in focus on the gg at the time, it is possible there is a significant shift between the position of the gg and the position of the film plane when the film is loaded. You can check this as follows. Tape a newspaper classified section to a wall. Draw a vertical line in the center. Put your camera about 6 feet from the wall. carfully level it, and point it at a 45 degree angle to the wall centering the line. Carefully focus on the line. Put the film holder in. Take a picture with the lens wide open, and try to provide enough light so that you can use a relatively fast shutter speed, thus minimize the effect of camera shake. Examine the resulting picture on a light table and see where the letters are sharp. Using a 2-4X loupe it should be about one to two inches. It should be roughly centered on where you focused. If it isn't, that means the film position is way off from where the gg is.

Let me make some additional comments. First, with a 135 mm lens at f/45, the hyperfocal distance is about 4 meters. That means everything from 2 meters to infinity should be in focus if you focus on the hyperfocal distance. That assumes a coc of 0.1 mm, which would be about right for looking at your image on the gg with 2 X magnification. If what you posted is close to the full frame, that figure would also be about right. Even if you used a 4 X loupe, that would effectively reduce the coc to about .05 mm and double the hyperfocal distance. Without being there and doing it myself, I can't be sure, but it is hard to believe you so messed up the focusing so that you were focusing way in front of the fence. That lends strength to the suggestion that the film was not positioned properly with respect to the gg.

Let me also address the issue of diffraction. At f/45 the resolution limit imposed by diffraction would be about 1500/45 ~ 33 lp/mm. That should allow something like a 5 X magnification before you would begin to see any fuzziness. It would also affect the entire frame, so nothing would be completely in focus, but of course defocus would add to it as you left the exact plane of focus. I don't think the fuzziness in what you posted could be from diffraction, unless it is a very small crop of the entire frame. With a focus spread of 4 mm, and the focus positioned halfway between the near and far point on the rail, the coc at those points should be about 2/45 ~ .04 mm and the resulting resolution about 22.5 mm. The combination should produce something like 18 lp mm in the film. It would require about a 4 X magnification before you began to see the result.

Finally, let me comment on your use of Hansma's method of choosing the f-stop. That method tries to give you the best result you can expect when combining the defocus at the near and far points with the effect of diffraction. You don't make things better by stopping down an additional stop; in principle, you make them worse. if you accept Hansma's analysis, his recommendation should be taken to be the smallest possible aperture to use.

[sanking]

Steve, you mentioned, "I am also a fan of the gg brighteners as most of them will brighten the image by 2 stops."

I tried to find some info about this, but came up with nothing: what do you suggest?


Go to http://www.largeformatphotography.info/gg.html for some options on ground glass brighteners.

I personally prefer the Boss screen to all other types of brighteners.

Sandy King

[Brian Ellis]

Steve, you mentioned, "I am also a fan of the gg brighteners as most of them will brighten the image by 2 stops."

I tried to find some info about this, but came up with nothing: what do you suggest?

I'm not Steve but I've been following this thread and since Steve hasn't responded yet - what "info about this" are you looking for? Info about viewing screen brighteners (which except for the BosScreen are all variations of Fresnel lenses) or info about the 2 stop effect? If you're looking for information about bright screens in general, there have been many threads about them in this forum. A search should give you more information than you wanted to know. If you're looking for information about the 2 stop statement, I don't know the source for that, perhaps Steve's personal experience.

[steve simmons]

Sandy's reference is a good one but it is a little dated. Wisner has been out of business for a couple of years.

There are several choices. If you do contact someone and get put off by some comment about them being so busy it will take weeks to fill your order just move down the line. There are too many good options to have to be made to wait like that.

steve

[Leonard Evens]

For Steve Simmons:

First, don't treat this as an attack. I believe your methods work, but I've personally never been able to get them to work.

First a clarification. The focus spread is the distance in mm on the rail between the positions where the near point and far point come into focus. The recommendation elsewhere in the large format web page is to focus halfway between those positions. This is also a very old method which has been used by large format photographers for quite a long time.

The focus spread is also used to detrmine the proper f-stop. There are different ways to do this, but many people use a method introduce by Paul Hansma. It tries to give the best result at the near and far poitns when defocus and diffraction are combined. It is also described elsewhere on the large format page.

Second, a question. I've tried your method for focusing and determining the f-stop several times, but I've never been able to get it to work. In the recent View Camera Magazine, there is an article by someone explaining how he (she?) used the method, and I can't argue with the results. I believe iit works for many people. Perhaps I am still doing something wrong.

First, I find it hard to judge when the near and far points are equally out of focus, but I haven't tried it with a loupe. I will give it a try, but it seems as if it would be more work that way than just focusing halfway between the near and far points. More important, I can't see much of anything when I stop down below f/22. I don't think accusomizing myself to the dark is an issue because I do that anyway, I am rather amazed that someone can stop down to f/45, as in the View Camera article, and judge whether the near and far points are in focus or not. Perhaps it is just my 74 year old eyes, but others have also said they can't see much of anything below f/16 to f/22. There may be some other clues that I don't know about.

Finally, I have a question about the use of a loupe in doing any of this. When you magnify the image, you in effect demand higher sharpness. An 8 X loupe is equivalent, I think to producing a 32 x 40 print and looking at it close-up. If you do that you are going to reduce the depth of field significantly. You would end up choosing an aperture appropriate for that kind of situation but way too small for viewing a smaller print or the same print from a more normal viewing distance. In the process, you would magnify the effect of diffraction, which also will be more apparent when viewing a large print from so close. I suspect that in practice, neither you nor your students are actually doing that and in fact you are coming up with more reasonable apertures for the situation. So I think there is something else going on which I don't understand.

[Vaughn]

If I may hijack the tread a little...

What is the trade-off (if any) with using GG brighteners? Usually, if one gains something, one loses somewhere else. Is that the case with GG brighteners?

Vaughn

[Brian Ellis]

If I may hijack the tread a little...

What is the trade-off (if any) with using GG brighteners? Usually, if one gains something, one loses somewhere else. Is that the case with GG brighteners?

Vaughn

There are quite a few trade-offs depending on the particular brightener being used. As I mentioned before, all brightening screens are some form of Fresnel lens except the BosScreen (and it isn't technically a brightening screen).

One trade-off is the fact that when using a loupe the Fresnel lines become magnfied which can make it difficult to focus. Another is that you pretty much have to keep your eyes "on axis," i.e. view the screen from a straight-forward position. If you move off-axis, i.e. move your head to one side or another, for example to better see the edges of the image, things start to get darker. A third is that a Fresnel is actually a lens and ideally should be matched to the focal length of the lens in use. Of course few photographers carry around a separate Fresnel for each lens they use so you end up compromising and using a Fresnel that roughly matches some of your lenses but not others. Often that means a Fresnel that works well with normal and longer lenses but not so well with wide angle lenses. When a longer focal length Fresnel is used with a short focal length lens the effect produced can be a bright inner circle surrounded by darkness and it can become difficult to see the image well enough to compose.

Some bright screens are better than others in regard to these trade-offs. The Maxwell screens have kept the trade-offs to a bare minimum and I found those screens to be the best of the ones I've used (which is quite a few), really the only brightening screen I was completely happy with. I also liked the BosScreens I've used but as mentioned before, those don't actually brighten the image, they achieve their effect by spreading the image evenly across the screen so that it becomes easier to see. But Maxwell screens are expensive, about $250 and up, BosScreens aren't cheap either, about $150 and up.

[Los]

leonard, thank you very much for that explanation. i have been trying the hansma method for several months now. on several occasions i found the far limit to be a bit short, so for this image (which was a test) i thought i'd stop down a little more. on the other images i've made cropped optical enlargements to 8x10 and 8x12, and was satisfied with overall sharpness and OOF areas in the prints. this time i noticed an overall bit of fuzziness that seemed to affect the sharp parts of the image as well. this is what Brain described as the look of a diffraction affected image. it seems i will have to make a print to see how much i notice it, and if it is acceptable for me.

i apologize for not attaching the full frame of the crop. i realize it helps give perspective to the smaller portion. it seems everyone that responded does not notice diffraction fuzziness in their prints, so i am encouraged.

http://home.mindspring.com/~carlosjackson/sitebuildercontent/sitebuilderpictures/dof_unsharp.jpg

[steve simmons]

The halfway point is not truly accurate unless you are working very close with a reproduction ratio close to 1:1. As the subject moves farther away the halfway point is no longer the correct place to focus.

Try this process with a loupe, 4X is plenty. Just act slowly and quietly under the darkcloth.

I am not saying this works for everyone. I can do the math but would rather look and see. This works for some and not for others. Some people like cheesecake and some like chocolate. It is a big world and diversity makes it interesting - I read this forum for many reasons - one of them is to learn other approaches.

steve

[Leonard Evens]

The halfway point is not truly accurate unless you are working very close with a reproduction ratio close to 1:1. As the subject moves farther away the halfway point is no longer the correct place to focus.

Try this process with a loupe, 4X is plenty. Just act slowly and quietly under the darkcloth.

I am not saying this works for everyone. I can do the math but would rather look and see. This works for some and not for others. Some people like cheesecake and some like chocolate. It is a big world and diversity makes it interesting - I read this forum for many reasons - one of them is to learn other approaches.

steve

I will give another try with a loupe. I should admit that, on the basis of your recommendation, I often do stop down as far as I can see anything, say to f/16 or f/22, depending on the light, to see whether the near and far points are coming into focus. If, for example, I have already decided on the basis of my simple "math" that f/32 was a reasonable choice, I can begin to see at f/22 if that is reasonable. But I still can't see much of anything at f/45 or even f/32. As I said, that may just be a function of age.

I hope we are not talking about different things with respect to the proper focus point. I am talking about position of the standard along the rail or caemra bed. For that, it is correct that the halfway point is not the correct poiint at which to focus. The correct point is the harmonic mean of the bellows extensions or image distances for the near and far points. But, except in rare circumstances which don't often occur in practice, e.g., exteme close-ups with very short focal length lenses, the harmonic mean is very close to the midpoint, so it isn't worth the extra effort to calculate where it is. (That is assuming you even know what the harmonic mean is.)

I can't be sure what you are thinking, but from what you say, I would guess you are talking about the focus point for subject distances in the scene. It is true for close-ups that the focus point is roughly halfway between the near point and the far point in the scene, and that as you increase the distance from the lens, you devaite more and more from the that position. For example, when focused at one third the hyperfocal distance, there is twice as much far depth of field as near depth of field. And, of course, if your far point is at infinity, the far point is infinitely far away from the focus point, so it would be nonsense to say the latter is halfway or any other distance to the former. (Aside: There is a nice symmetry betweem subject and image distances. The proper place to focus in the scene is also the harmonic mean of the distances to the near point and the far point. But few people woudl be willing to calculate that when taking a picture.)

[Leonard Evens]

Los,

Looking at the complete scene, I see another possibility. It is not possible to be sure without examining the image myself, but it seems that the wicker fence on the right is going out focus fairly quickly, but the picket fence in the background is still in reasonably good focus. If so, it is possible you have a slight swing, i.e, your standards are not paralel. If so, the exact subject plane might be closer to you on the right than on the left, and that might explain what you see. Often, the detent or zero positions for the standards are slightly off because of play.

You can check whether the standards are parallel as follows. Turn the tripod so the lens axis is pointing straight down. When that is the case, a torpedo level placed agains the lens barrel edge will be level in all directions. Then check with a small level right on the gg. It should also be level in all directions. You should be able to make slight adjustments to get them parallel.

You should also do the test I described to see if the gg plane and film plane coincide.

Finally, let me note that the crop you showed represents something like a 5 X magnification. With only a 600 ppi scan, I wouldn't expect the scan to retain enough detail to really analyze what is going on. Also, remember my warning that if you magnify the image enough, you are bound to see some things going wrong. If you are using a 5 X or higher loupe to examine the negative, then you shouldn't really expect what you see in the negative to be perfectly sharp. On the other hand, the near point and far point you used should look equally bad, and they don't appear to in what you posted. So I think there is something going on, either focusing error from shift of ground glass relative to the film or a slight swing or both.

[Los]

leonard,

i did the test you suggested for normal-ness. the front standard was indeed swinging by a little less than five degrees and not sitting in the detent. i was doing the test for dof and thought i had zeroed all the movements. must have bumped it somewhere. swing was locked, but not zeroed. i'd say your eyesight is pretty darn good. once the swing was fixed, the levels were all good.

still, i would think f45.3 would mask such a slight swing. from what you see in the crop, would you expect greater overall sharpness with diffraction? (mind you, the scan if from a flatbed and has not been sharpened). i am using a toyo loupe with a magnification of 3.6x to look at the negatives.

if you don't mind my asking, what has been your personal experience with diffraction at deep stops and modest sized prints, say 20x24 or 16x20?

[Dick Hilker]

Thanks to all for the clarification on GG brighteners. As a newcomer to LF, I assumed they might be something that could be used to brighten an existing GG.:o

[steve simmons]

5 degrees of swing is actually a lot and that will cause a problem with a straight ahead subject.

Stop worryng about diffraction. It is MUCH less a problem than having only part of the scene in the dof area.

You need to read some of the basic texts on lf. Try User's Guide to the View Camera by Jim Stone, Jack Dykinga's book Large Format Nature Photography, or my book Using he View Camera.

You are confusing your concepts and don't really understand enough about how the camera and lenses function yet. Do some homework, take a class, etc.

steve simmons

[Michael Kadillak]

You can also use a mini mag flashlight with the top taken off exposing the bulb as a focusing tool. Put a couple either on your plane of focus (near and far) or where you want to evaluate focus near and far and it will go from a diffused bulb to a point light source when in focus. Works like a champ.

[Dave Jeffery]

Re: Maxwell screens

I spoke with Bill Maxwell recently and I am wondering if the regular screen is the way to go or to buy the ultra- brilliant model. I am probably going to order the ultra-brilliant unless Ellis or anyone else thinks the regular screen is better. It's for an Ebony 45SU using 110XL, 150 S and 210 lenses for landscape photography.

Thanks as always!

[Leonard Evens]

leonard,

i did the test you suggested for normal-ness. the front standard was indeed swinging by a little less than five degrees and not sitting in the detent. i was doing the test for dof and thought i had zeroed all the movements. must have bumped it somewhere. swing was locked, but not zeroed. i'd say your eyesight is pretty darn good. once the swing was fixed, the levels were all good.

still, i would think f45.3 would mask such a slight swing. from what you see in the crop, would you expect greater overall sharpness with diffraction? (mind you, the scan if from a flatbed and has not been sharpened). i am using a toyo loupe with a magnification of 3.6x to look at the negatives.

if you don't mind my asking, what has been your personal experience with diffraction at deep stops and modest sized prints, say 20x24 or 16x20?

5 degrees is actually a fairly large swing for a 135 mm lens. Also, when you swing, the rules about where to focus are a bit different. First you choose points to the left and to the right which you want to be in adequate focus. The plane of exact focus should go roughly halfway between those points. (See below.) You set the swing so that the plane of exact focus does that. Once you have done that, swing the plane of exact focus to the left and right by moving the stnadard, i.e.. by focusing, until it passes through each of the chosen points to the left and to the right, note the position on the rail for both and determine the focus spread between. Then refocus halfway in between. This should get you back to the plane of exact focus you decided on or fairly close to it. Now use the focus spread to determine the f-stop as usual.

In your particular example, you want the wicker fence on the right to remain in focus, and it isn't, so you probably set the focus in the wrong place for a swung lens. After you had set the swing, you may still have been concentrating on near and far, while you should have been concentrating on left and right. But, I'm not sure this scene is actually amenable to improvement by use of a swing. If you had set the focus position so that the wicker fence were in focus, then you might very well have found the meter and wall to the left going out of focus. My guess is that you would have been better off with no swing.

Let me describe more precisely how you should go about setting the plane of exact focus. Imagine a plane at some distance from the camera perpendicular to its unswung line of sight. Also, imagine two vertical lines, one to the left and the other to the right which define the limts of DOF at that distance. The plane of exact focus should split the region between those lines in two. (However, in some circumstances, you may want to favor one side over the other, and then you would move it closer to the desired side.)

As to my own work, unfortunately, at present, I can't print larger than 13 x 19 inches. I did make one 25 inch wide print by printing three 8 1/2 x 11 sections which I matched at the edges while mounting. Everything in that print looks quite sharp, even close up,. But the subject in this "triptych" is the facade of a building, so all I had to worry about was focusing on one plane. When I look at my smaller prints under magnification, I see what I would expect, given the limitations of my scanner and printing process. I seldom find significant differences in sharpness between foreground and background. But of course, I am not perfect, and sometimes I get the focus wrong. One thing that I've noticed can be misleading, particularly when using a shorter focal length lens. If you look at detail under high magnification in the background, it may appear to be less sharp than similar detail in the foreground. But, of course, the same size object is much smaller in the background than in the foreground, so the foreground may appear sharper for that reason. But I consider this an artifact of looking at the image under too high magnification, and it doesn't bother me. If it does bother you, then you should the focus closer to your far point. When the far point is at infinity, Merklinger recommends setting it there, more or less on grounds of this nature. I don't personally buy his argument, but I do often adjust the focus point to emphasize what I consider important. Photography always involves some compromises, and you have to decide for yourself what you want to emphasize and what is not so important.

[Los]

leonard,

thank you for your insight. i plan to shoot another test and make a print. i'll be sure to share my results with you.

[terrylorch]

Google "hyperfocal distance" for maximum depth of field. I use a light-weight music stand and a tape measure, put the stand at the hyperfocal distance, focus, remove stand, and shoot.