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Don Wallace
4-Oct-2005, 10:03
What is a practical and simple way to calculate dof in the field? I do a lot of "people" photography (not just portraits) outdoors and bring a set of homemade plasticized dof tables with me to cover most situations. Is there a handheld calculator I can buy that allows me to get fairly precise dof answers? From what part of the lens do I measure?

Finally, are there any good primers on how to use dof effectively in real situations? I really don't want tons of math - just some basic info on "how to get that rock in the foreground in focus and the trees in the near distance out of focus."

Bob Salomon
4-Oct-2005, 10:08
Rodenstock makes a handheld calculator with DOF for all format from 35mm to 810 in level and inclined positions at several image ratios. The other side calculates Scheimpflug. Easily fits in a shirt pocket and has a mm scale ruler to measure the displacements between the near and far point on the gg and on the rail/bed.

jose angel
4-Oct-2005, 10:13
I run Vademecum on a Palm device. All the calculations you can imagine. I found this combo the best I have seen ever. Precise and relatively fast to use.

Walt Calahan
4-Oct-2005, 10:59
Jose, do you have the URL of the Palm calculator "Vademecum" that you can share with us. I Googled Vademecum and got toothpaste in Europe. HA!

Denis Pleic
4-Oct-2005, 11:07
Walt, the software is Bob Wheeler's:

http://www.bobwheeler.com/photo/Software/software.html

Denis

Dan Jolicoeur
4-Oct-2005, 12:05
D(mm) F

1--------16.6

2--------22.6

3--------32.2

4--------32.6

5--------32.9

6--------45.2

7--------45.4

8--------45.6

9--------45.8

10-------64

http://www.largeformatphotography.info/fstop.html

I have this chart taped to my ground glass protector taken from the above link on the front page of this forum.

I simply measure the Delta distance moved between the near and far focus, doesn't matter where you measure it, camera bed movement or calculated turns of a knob.

You may find it usefull to read the front page of this forum titled articles under "Taking the Picture"

Regards, Dan

Leonard Evens
4-Oct-2005, 14:28
The easiest way to estimate dof in the field is to use the so-called focus spread method. This is described in detail elsewhere on the large format webpage. What you do is focus on the nearest point you want in focus, note the position along the rail (or bed), then focus on the furthest point and do the same. The distance along the rail between those points is the focus spread. You then place the standard halfway in between and determine the needed F-stop based on the focus spread. Paul Hansma has suggested a method of balancing defocus and diffraction which yields the table that Dan gave above. I find that to be too conservative. Another rule which ignores diffraction says to multiply the focus spread by 10 and then divide the result by 2 to determine the F-number. I find that the best choice is somewhere between these two extremes.

A variation of this method due to Steve Simmons doesn't require any numbers at all. Focus so that the nearest and furthest points you want to be in focus appear on the gg to be equally out of focus. Then, using a loupe, stop down until those points come into focus. This works quite well if you don't have to stop down too far, but few of us can make out anything on the gg at apertures smaller than f/16 or f/22. It also can be used as a backup for the focus spread method.

In using the focus spread method, it helps to have a distance scale on your focusing knob. It is not too hard to put such a scale on your focusing knob. I describe how I did it for my Toho FC-45X at www.math.northwestern.edu/photos/pages/dofessay.pdf. Some Sinars have a scale marked in F-numbers on the focusing knob, and there is an alternate method based on the same ideas I've described here which you can use with it. The large format webpage has a description of how to make a Sinar type scale of your own, and how to use it.

Graeme Hird
4-Oct-2005, 16:23
"What is a practical and simple way to calculate dof in the field?

Use a loupe on your ground glass and set the aperture appropriately. DoF with LF gear is an esoteric concept in any case.

Cheers,

Dan Jolicoeur
4-Oct-2005, 16:49
DoF with LF gear is an esoteric concept in any case.

Hence the Category: Beginner's Questions.

What is wrong with expanding the inner circle?

paulr
4-Oct-2005, 18:03
"Paul Hansma has suggested a method of balancing defocus and diffraction which yields the table that Dan gave above. I find that to be too conservative."

just intuitively, those numbers look incredibly conservative to me. i'm guessing i'd be shooting most of my pictures at f64 if i followed that, but i rarely go below f22 or f32.

has anyone else actually experimented with this kind of thing?

Michael Gordon
4-Oct-2005, 18:23
Practical and simple? Unless you're bad at determining visual distances, then focusing 1/3 into your scene (closest point to farthest point) and stopping down will always simply do the trick. Why make making images an exercise in calculus?

As for your second question, a wide aperture and camera movements. http://www.mgordonphotography.com/NPN/grass_lg.jpg

4-Oct-2005, 19:37
I agree with Michael. All you need to do is watch the ground glass, use your movements (only if necessary or if placing a plane of focus will improve the depth of field) and stop down while viewing. I know several folks that shoot 12x20 that do not even own a loup for focusing. They do it all by simply watching the ground glass and can tune in the focus once composed in under 60 seconds.

You are making a photograph, not defending a thesis.

Try it.

Cheers!

Leonard Evens
4-Oct-2005, 22:15
The one third into the scene rule works for precisely one distance, when you focus at one third the hyperfocal distance. It clearly won't work when you want the far point to be at infinity. In that case, the total distance you want in focus is infinite, and what in the world is one third of infinity supposed to mean except infinity? It also doesn't work in the close-up range where the range in focus in front of the exact plane of focus is pretty close to equal to the range in focus in back of the exact plane of focus.

Arithmetic is not calculus. If you use an exposure meter, then you shouldn't have much trouble with any method based on focus spread or even, if you insist, with dof tables.

Graeme Hird
4-Oct-2005, 22:59
"Hence the Category: Beginner's Questions.

What is wrong with expanding the inner circle?"

My thoughts exactly Dan. Things get very complicated when tilts and swings are applied to the camera - tables and formulae quickly lose their relevance.

As a beginner, it is better for Don to use the simplest method which (in my opinion) is observing the ground glass for the desired DoF. Your table and method work really well when the user understands the concepts behind them, but when starting out it's better to use your eyes.

Cheers,

Leonard Evens
5-Oct-2005, 09:47

Like everyone else, I've gone through all of this, and I seem to have made all possible mistakes. I think that those recommending using your eyes are mostly old timers which lots of experience who may have forgotten just how hard it is for some of us, at least, to interpret what we see on the ground glass. Although I'm a mathematician, I didn't start out in photography using any mathematics or optics beyond the usual basics about f-stops and exposure. I only used more complicated methods when I found I couldn't make do with the purely visual. And, I certainly didn't try to use the most advanced methods I know about to help me, just the simplest things which work. These employ nothing beyond basic arithmetic and in a few cases some elementary algebra as taught in high school. Although it is easier for me personally just to work out the algebra myself, that is not actually necessary since it is readily available in the form of simple formulas, calculators, or tables.

In fact, the more experience I get, the more I do in fact rely just on what I see on the ground glass, but it is important to note that this is only possible because of the experience I've gained. Even if I were devoid of any knowledge of optics and hadn't read the very useful information about focusing and dof on the large format web page, I would have eventually gained that experiential knowledge through trial and error, but it would have taken much longer.

If you think about using the ground glass image, you can see there are some problems with relying on "what you see". One example is that, if you stop down past about f/16 or f/22, you are not going to be able to see much of anything when trying to judge depth of field. I thought this was just my bad eyes, so I posed a question about this in a large format forum and found that I was about average, or perhaps a little bit better than average, in how well I could see. Another problem involves the use of a loupe. As we all know depth of field depends crucially on the choice of coc in the film plane. But when you view the image on the ground glass, with or without a loupe, there is an implicit coc involved in what appears to you to be in focus. It would be a lucky coincidence if this was the same as a coc based on a standard for a final print. Moreover, when you magnify the image with a loupe, you in effect decrease the visual coc. Of course, through experience, you may hit upon a combination, which if used consistently, will give results that work for you. But I think it is naive to assume that a beginner is going to do that right immediately. There are of course some gifted individuals who can get it right by proceeding visually without any other aids and get it right from the beginning. But I think few beginners fall in this category. That is why the recommendations in the large format photography webpage are so useful.

There is also the additional point that thinking too much about technique can distract you from the picture, which of course is the point of it all. I think that different people react differently in such matters. For me at least, thinking about issues like depth of field, light values as in the Zone System, and other such matters, enhances my understanding of the scene. I see things that would otherwise escape my attention until I examined a final print and wondered what I did wrong. Let me give an example. I recently broke down and got a center filter for my 90 and 75 mm lenses. It isn't always necessary, but one certainly can't tell by examining the gg image whether it will be. But it is not hard to estimate the amount of the rise and from that I can get some idea of how close I am getting to the circumference of the circle of coverage. Of course, that won't be important for some images, but in other cases, such as in architectural photography, it can be very important. This doesn't distract me from other aspects of choosing the point of view---probably the most important choice----studying image on the gg, etc. It just takes a little longer, but large format photography is just like that. We don't put a premium on speed.

james mickelson
5-Oct-2005, 11:55
I'm always amazed at this question when the answer is so simple. It ain't rocket science. "The ground glass doesn't lie !" Look at the ground glass and it will tell you exactly what is in focus and what isn't. Without a tape measure the tables aren't that accurate anyway. You can make your own scale and glue it to your focusing rail. Focus on your subject when it is close and mark your rail. Focus on some middle ground object and mark your rail. Pace off the distance for reference. Then focus on an object at a farther distance and son on until you are at infinity for that lens. Now everytime you need to focus quickly you have a reference to use. Easy. But I like the tried and true view through the GG.

5-Oct-2005, 12:12
Leonard:

I fumbled and struggled with various power loups and depth of field devices until it drove me nuts. I finally came to the conclusion that continuing to make it more complicated that it really needed to be was hindering my photography. After seeing Michael Smith and Paula Chamlee as well as Sandy King just "get it done" without giving it a second thought with the ground glass and their eyes I forced myself to leave all of magnifiers and accessories home and bit the bullet. The longer I trusted what I was seeing, the easier it was to make photographs. And no, not all that just look at the ground glass for focusing are old timers.

Seeing the image is a rather relative proposition. Sometimes you are looking at the "relationship" of wheither the fore and aft come in and out of focus proportionally so you know that you are dialed in. For some scenes I can step back from the ground glass (my eyes are not that good anymore either) and step down to f32 and descern the image quality. A good fresnel can help in this regard as can a good dark cloth that blocks out all of the stray light.

Let go of the rope and get back to basics.

Cheers!

james mickelson
5-Oct-2005, 17:38
Getting a good darkcloth and then reading literature about how the camera "sees" is something too many LF photographers fail to do and learn. Too many make this hobby/addiction/life passion too difficult. It's easy. I use a loupe but only after I set up my image on the GG and focus with my eyes. I have a good "dark" dark cloth with elastic around the camera end and velcro along the open edges on the bottom. I back away from the GG and focus. Up/down/left/right until the image is out of focus equally and then I rack the standards back and forth until I get it reasonably close. Then I use the loupe to check for critical focus. If I am using any movements, then this is just something you practice the hell out of until you learn it. Practice makes perfect. I spent a very very long time over the course of a couple years practicing just focusing the camera at home and on the road. Then when I went into the field, it was simple to get what I wanted quickly. Seldom do I miss an image because of technical issues. I'm ready to rock when I get to the field. Practice at home and learn to set up quickly. Use the side of a building or fence to practice swings and a tall building, a bush and trees to practice tilts. Learn the fundamentals of Schiemflug so you can see at a glance which way to swing or tilt your standards both front and back so you can set the camera close as you set it up. Don't worry about the math as it just gets in the way. It's intuitive once you understand what it does and how the lens sees. But practice it a lot.