Focusing question

[Deliberate1]

Friends, I am exploring along the learning curve. One of the issues I am working on is depth of field. With my MF gear I have cards showing the hyperfocal and DOF data, but no such aids with LF gear. So the steps I followed today as follows:
1. deploy camera (Toyo 45A)
2. attach lens and move front standard to appropriate mark on the bed (eg. 90mm line)
3. open lens up and rough focus on primary subject (if not an infinity shot)
4. fine tune with loupe
5. (here's my revelation) while holding loupe, stop down lens to bring background, for example, into focus, or to what ever degree of clarity is desired.
6. Do aperature priority meter reading (assuming speed is not an issue).

If I have this right, will the ultimate image have the same focus and DOF as I see on the ground glass? Have I missed something in this process that would give me a result different than what I see?
Appreciate the feedback.
David

[Ralph Barker]

I think you have a good grip on the basics. There are other techniques described in articles on the Home Page (see link in the blue navigation bar), too. The big issue is often whether you can still see anything useful at the desired taking aperture. So, having other methods at your disposal is helpful.

There are also various DOF calculators available online, so you could print out a chart for your individual lenses. The one I use was written in HTML, so you can modify the various assumptions used to suit your own preferences.

http://www.rbarkerphoto.com/DOF2.html

[Deliberate1]

Ralph, thanks for the reply. I have used that very DOF calculator for my MF rig. So If I do similar cards for my LF lenses, how does one determine distance without those helpful hash marks on the MF lenses? Analog way is eyeballing it, I suppose. Digital would be some sort of rangefinder? Regards, David

[Donald Miller]

Friends, I am exploring along the learning curve. One of the issues I am working on is depth of field. With my MF gear I have cards showing the hyperfocal and DOF data, but no such aids with LF gear. So the steps I followed today as follows:
1. deploy camera (Toyo 45A)
2. attach lens and move front standard to appropriate mark on the bed (eg. 90mm line)
3. open lens up and rough focus on primary subject (if not an infinity shot)
4. fine tune with loupe
5. (here's my revelation) while holding loupe, stop down lens to bring background, for example, into focus, or to what ever degree of clarity is desired.
6. Do aperature priority meter reading (assuming speed is not an issue).

If I have this right, will the ultimate image have the same focus and DOF as I see on the ground glass? Have I missed something in this process that would give me a result different than what I see?
Appreciate the feedback.
David

I don't see where you are using movements to beneficially modify the plane of maximum focus. In other words, as I read what you wrote, you seem to be using LF as only a larger incarnation of a single lens reflex camera. I would suggest inclusion of these factors (movements) into your working regimen.

In my methodology, stopping down the lens only occurs after the greatest degree of focus through use of movements is attained.

To answer your question, what you see on the ground glass is what you get. I have never used depth of field tables in almost thirty years of LF usage.

Good Luck,

[Deliberate1]

Donald, thanks for yours and fair points. My step 4, fine tuning, would include front tilt to maximize focus. I have not quite figured out rear tilt. Care to educate me? Obliged. David

[Donald Miller]

Donald, thanks for yours and fair points. My step 4, fine tuning, would include front tilt to maximize focus. I have not quite figured out rear tilt. Care to educate me? Obliged. David


Tilt is only one of the movements available to maximize focus. Swing being another. Shift is a movement that has it's primary effect on composition and not focus. Rise and fall have the same use as shift...primarily compositional aids.

As a rule of thumb, rear movements (swing and tilt) have the effect of altering relationships (near objects can be brought to loom or conversely diminish in relationship to far objects) as well as altering plane of focus whereas the front movements will not do this. That is the short course. Good luck on your journey...beyond all else have fun.

[Ralph Barker]

You probably already know this, David, but tilts don't really "maximize" focus, but rather make the best use of it by moving the plane of focus from the perpendicular. DOF essentially becomes a wedge, the narrow end of which is near the camera. Rear tilt can be used in a similar manner to front tilt, but tilting the rear changes the geometry of objects within the frame. In either case, one has to watch out for objects that are above or below the plane of sharp focus, and outside the "wedge" of DOF. Sometimes, keeping the standards plumb is the best approach.

While it is possible to use a rangefinder to determine distance to objects within the frame, such as a laser rangefinder, doing so is only beneficial when relying on DOF tables. The focus-far, focus-near, split the difference approach described in the article on the home page gets around that when combined with viewing the GG when stopped down.

You may find that a combination of techniques, suited to your own working style, will be convenient.

[Leonard Evens]

First, let me suggest that you study the material on focusing at the lfphoto.info web page. In particular look at the near point, far point method for focusing and setting the f-stop for desired depth of field. Many people find it more accurate than looking at the ground glass while stopping down.

But, let me go back to your original question: If you focus as carefully as possible and then stop down to your taking aperture to estimate what is in focus, will what you see on the ground glass accurately reflect what will be in focus in the final print.?

The answer is that it depends on how you look at the image on the ground glass. Generally, if you use a loupe, you reduce the region which will appear in focus relative to what you would see under normal circumstances in viewing the final print. How much depends on a variety of factors, such as how much magnification you use in viewing the ground glass, how much you enlarge to print, and from how far away you view the final print.

So if you are mainly concerned about whether what you want to appear in focus is in focus, and you don't care whether or not more is, than what you are doing may work fine. (But see below.)

On the other hand, if you interested in restricting your DOF, then you may end up with too much in focus in the final print.

Alternately, if you are interested in using the largest possible aperture (smallest f-number) that you can get away with---in order to shorten the exposure time, for example--- then using a loupe to estimate DOF may lead you to stop down too far. If you used a 2 X loupe, it would probably be just about the right, if you used a 4 X loupe, it might overestimate by one stop, and if you used an * X loupe, you might overestimate by 2 stops.

Since viewing the ground glass is not the same as viewing a print, other factors may come into play which operate in the other direction. For example, the image gets dimmer as you stop down and that may make it harder to estimate sharpness. Whether it under or over compensates for the effects I mentioned above depends on so many factors that it is impossible to be sure of what will happen.

So, the final answer has to be that you should try it. Make some exposures and produce 8 x 10 prints from them which you should view from about 12 inches. Decide whether the method you use gives you approximately the right depth of field. If not adjust the procedure by stopping down more or less than the gg image suggests until you get it right.

Let me just add some more information that you might find useful. It is a special case of the near, far method mentioned above. There is a standard distance along the rail, which depends on the f-number and your criterion for what is sharp. If you focus that distance further back from the infinity position, then you will be focused on the hyperfocal distance for your circumstances. A good starting point for this crucial distance is one tenth of the f-number. So, if you are going to stop down to f/22, then you should move beyond the infinity position by 2.2 mm on the rail or camera bed. But for some people it might be as small as one twentieth of the f-number.

It is hard to measure such small distances directly on the rail. But most view cameras use a gearing mechanism for fine focusing which allows for more precise control. It is possible to make a focusing scale which you attach directly to the focusing knob and use that. I did that for my Toho FC-45X----a description is at www.math.northwestern.edu/~len/photos/pages/dof_essay.pdf
----and I can measure distances on the rail to within two tenths of a mm accurately. I find it invaluable in my work.

[Deliberate1]

Gentlemen, I am greatful for your generous advice. So much mystery at this point in my LF adventure. Leonard, I will certainly look at the near/far technique, which was already on my to do list. I did check out that article from Northwestern, and broke out into a cold sweat over the math. I suspect it will all seem a bit less ominous after a few readings. Again, obliged to you all. David

[steve simmons]

May I suggest some reading

Jim Stone's User's Guide to the View Camera
Jack Dykinga's Large Format Nature Photography
my book Using the View Camera.

check your local library.

After you have done the initial focussing, etc. I teach my workshop students to focus so that the closest thing you care about and the farthest thing you care about are equally out of focus. This will place the plane of focus in the propler location between these two point/objects. Then, as you stop the lens down, the dof area will spread to include these two points/objects at the same time.

steve simmons

www.viewcamera.com

[Leonard Evens]

Gentlemen, I am greatful for your generous advice. So much mystery at this point in my LF adventure. Leonard, I will certainly look at the near/far technique, which was already on my to do list. I did check out that article from Northwestern, and broke out into a cold sweat over the math. I suspect it will all seem a bit less ominous after a few readings. Again, obliged to you all. David

I think you can skip the math. The part of the article I was referring to was where I explained how I made a scale to put on my focusing knob. Basically all you have to do is measure the distance the standard moves on the rail or camera bed when you turn the know one full turn, as well as the circumference of the knob. The ratio of the second distance to the first tells you how much distances on the rail are magnified on the scale. Using that information, you can make marks on the scale in mm and, we hope, tenths of a mm, corresponding to such movements on the rail.

Looking at what I just wrote, I can see it is not terribly clear, but I hope when you actually do it, it will become a lot clearer.

[John Berry]

Donald, thanks for yours and fair points. My step 4, fine tuning, would include front tilt to maximize focus. I have not quite figured out rear tilt. Care to educate me? Obliged. David The best education on that is next time out, try it both ways. First use front tilt to get the image you want. Then square up the front and use back tilt to get what you had with front tilt. You might find they have different character. Rear tilt will change perspective. I use it a lot on purpose.

[Nathan Potter]

Leonards knob scale idea is one I've used on some occasions, especially for macro work. The idea is similar to that used on vernier calipers and micrometers to increase the accuracy of linear measurements. In the case of rail measurements on view cameras the improvement in rail position accuracy is derived from the ratio of the knob circumference to the geared circumference (the gear that moves the standard along the rail for focusing). This can be very significant as Leonard points out. For example, with the lens wide open (so the subject material is very visible) you can focus on the near and far subjects that you want to be in focus and note the delta in the film plane position from the accurate reading on the focusing knob. If you have generated a chart of DOF for a particular COC and f/no. and the lens you are using then you can set an approximate center of focus using a rail position intermediate to the near and far readings. It's all a PITA so I seldom go to all this trouble.

Nate Potter

[Leonard Evens]

Leonards knob scale idea is one I've used on some occasions, especially for macro work. The idea is similar to that used on vernier calipers and micrometers to increase the accuracy of linear measurements. In the case of rail measurements on view cameras the improvement in rail position accuracy is derived from the ratio of the knob circumference to the geared circumference (the gear that moves the standard along the rail for focusing). This can be very significant as Leonard points out. For example, with the lens wide open (so the subject material is very visible) you can focus on the near and far subjects that you want to be in focus and note the delta in the film plane position from the accurate reading on the focusing knob. If you have generated a chart of DOF for a particular COC and f/no. and the lens you are using then you can set an approximate center of focus using a rail position intermediate to the near and far readings. It's all a PITA so I seldom go to all this trouble.

Nate Potter

I don't see what you find so difficult about it. For focusing, you just set the standard halfway between the positions for the near and far points. To determine the proper f-number to use, you use the focus spread, or distance in mm between the near point and far point. If you then follow the approach recommended on the lfphoto.info web page, yo appeal to Paul Hansma's table, which you carry with you, from which you read the f-number from the focus spread. This method supposedly balances diffraction against defocus. But, ignoring diffraction, you can get a quick estimate by multiplying the focus spread by 10 and dividing the result by 2. (That assumes a coc of 0.1.) For example, suppose the focus spread were 4.6 mm. The calculation gives 10 x 4.6/2 = 46/2 =23. So you would stop down to f/22, or if you wanted to hedge your bets, a hlf stop to a stop further.

I do this all the time, and the whole process, including focusing on the near and far points, takes less than a minute.

[Doremus Scudder]

At the risk of shameless self-promotion...

I wrote an article for View Camera Magazine about using basic movements with the field camera that might be of interest to you. It purposely avoids mathematics and uses a strictly visual approach.

You can find it on the free articles page of the View Camera web site. Here is the link:

http://www.viewcamera.com/documents/FieldCameraMovements.pdf

You can download the pdf. document.

One note: Leonard Evens pointed out to me after the article was published that the illustrations of the depth of field "wedge" are not representative of the true situation. I showed them as flaring out when in reality they are simple wedges with straight edges. The illustrations are still useful for helping visualize how depth of field works when movements are applied.

I also use the focus-spread method for finding the optimum f-stop. I would second the above suggestions to dig through Mr. Hansma's article on the LF home page. I have made stickers for my cameras with the f-stop tables as well as adding millimeter scales to a couple.

The drill is easy: Apply all the movements with the lens open, then pick your near and far points, note the distance in millimeters between the near and far points, position the focus exactly at the midpoint, read the appropriate f-stop from the table, stop down, meter, and shoot.

Hope this helps.

Best

Doremus Scudder

[Nathan Potter]

Leonard, I didn't explain the PITA very well. Over the years in getting away from industrial type photography where I was used to employing a lot of technical stuff I've come to focus more on fine art photography. So now when I'm in the field my mind is totally consumed by the subject matter and I find any consideration of technique seems to be subservient to finding and framing the scene. I can't explain it well but in my mind there seems to be a conflict between the technical and the art that I can't handle simultaneously. I realize that at times this approach is detrimental to a well framed image and maybe it's just a phase in my photography.

Nate Potter

[timparkin]

Leonard, I didn't explain the PITA very well. Over the years in getting away from industrial type photography where I was used to employing a lot of technical stuff I've come to focus more on fine art photography. So now when I'm in the field my mind is totally consumed by the subject matter and I find any consideration of technique seems to be subservient to finding and framing the scene. I can't explain it well but in my mind there seems to be a conflict between the technical and the art that I can't handle simultaneously. I realize that at times this approach is detrimental to a well framed image and maybe it's just a phase in my photography.

Nate Potter

Heh... by your definition, the whole of the 'craft' of large format use is a PITA for me (having only started last October). Hopefully, all aspects of it will become second nature sometime in the next decade. I've distilled the focus knob scale rules into a simple Ebony rule of thumb... half a turn is f/45, quarter of a turn is f/32, 1/8 turn is f/22, and a wiggle is f16 :-)

Tim

[robert amsden]

The BtZS* software for a pda will figure it based on f stop and subject distance.

[ignatiusjk]

Dear deliberate1, what size lens you have on the camera also matters the angle of view the lens has will determine if you need to use the movements. The old rule was focus 1/3 of the way in a stop down to f32. With LF it's important not to complicate things.Sometimes the more we think the worse it gets.

[Bill_1856]

http://bobatkins.com/photography/technical/dofcalc.html
The most important thing to remember is that DOF is about 1/3 in front of the principal object, and 2/3 behind it.

[Leonard Evens]

http://bobatkins.com/photography/technical/dofcalc.html
The most important thing to remember is that DOF is about 1/3 in front of the principal object, and 2/3 behind it.

As with most rules of thumb, this is true only in special circumstances. For example, if you focus at the hyperfocal distance than everything will be in focus from half that distance to infinity. I don't know in what sense one could say that the amount in focus in front, which is half the hyperfocal distance, is half of infinity which is the amount behind.

Similarly, if you are close enough to the lens, and that could include normal portraiture distances as well as genuine close-ups, the amount in focus in front is very close to the amount in focus in back.. So we see that in general that ratio can go from 1:1 to 1:infinity. Of course, somewhere in between it will be 1:2, and in fact that distance turns out to be at one third the hyperfocal distance.

Let's look at a typical example. Suppose the focal length is 150 mm, we choose a coc of size 0.1 mm, and we stop down to f/22. Then the hyperfocal distance is about 10.24 meters., or 38.8 feet. If you were focusing at about 11.6 feet, then the 1/3, 2/3 rule would apply. The front DOf would be about 3.22 feet and the rear DOf about twice that or 6.44 feet. That might be appropriate for a middle distance scene, but it wouldn't be for a typical landscape.

Since this rule is so often quoted, I've often wondered what people using it are actually doing. I presume that in some perceptual sense on the gg, the front and read DOF appear to satisfy this rule, although if you made measurements they wouldn't. Another possibility is that this rule tells you to expect less depth of field in front of where you focus than in back, and in landscapes that is typically going to be the case. Perhaps someone who uses this rule can explain what he actually does. That might be enlightening.

[Dave Jeffery]

I made a focusing knob as suggested in the article on the LFP homepage and it was well worth the effort as it works perfectly.

When focusing without movements just focus on the far, focus on the near and then split the distance spread on the scale and possibly a hair slightly closer to near focus. The optimal F-stop is marked on the scale. A quick check on the ground glass with a loupe confirms the focus is correct. Fast and easy.

I cut down half of a PVC pipe coupler and customized things with a carbide cutting tip on a dremel tool. A piece of PVC pipe with a split in it, which has the focusing scale on it, rotates around a piece of pipe that slips onto the camera focusing knob. The grip is a slice of the PVC coupler grip. It's the same design as in the article but is has the Home Depot look.

There is a focusing scale provided that supposedly can be adjusted (stretched or shortened) for various focusing knob circumfrences but I didn't have much luck adjusting it and getting it accurate. I mounted a mm ruler on the camera bed and marked the scale on the focusing knob as I turned it. One has to mark it while turning in one direction only. I took the paper scale off and made some copies and then taped it back on.

It works great!

Focusing using movements and the Schiempflug plane of best focus is another issue and method needed.

Good Luck!