front tilt and depth of field (WYSIWYG) ?

[adrian tyler]

this may be dumb question i know, but as i have never been too academic (prefering nature to acedimia) and will never calculate shoomenflug or dof in the field i'd just like to confirm the following:

when focusing on near and far objets on the gg, i can feel with my fingers the length of bellows movemet required in relation to the two objects.

when applying tilt to the same scene the length of bellows movement in reation to near/far object is in most cases substantilly reduced.

is this a reliable indicator that you'r gonna get more in focus, or would that be too simple?

thanks

fire at will!

adriantyler.net

[Jim Rice]

With tilt you are effectivly lengthening the bellows selectively. I've never had much luck with straight shiemphlug, as it tends to give me too much tilt (and swing). It will tell you what direction to go in. So I rely on the ground glass image to tell me when it's right.

[John Cook]

The short answer to your question is, “Yup”.

I spent a few decades in a commercial catalogue studio, banging out product photography on an 11x14 Deardorff with an 8x10 reducing back. On the really low budget catalogues, the boss allowed us only six minutes to arrange the products, light the scene and “blap it off”.

After eight or ten hours a day for several years of that, one learns to bump the camera with his elbow until it looks sharp. No time to agonize over some radical calculus formula. And computers had not yet been invented.

Many math-types enjoy the formulaic wizardry. And what works for them is just fine with me. But I don’t see that at the end of the day their stuff is any better focused.

[Leonard Evens]

You will get one plane in exact focus. When the lens plane is parallel to the film plane, so is the plane of exact focus. Depth of field refers to what is adequately in focus (according to some pre-chosen standard) in front and in back of that exact plane.

When you tilt the lens, the situation is more complicated. You don't need to be able to calculate, but you should have a feeling for the geometry, or else you will be working by hit or miss. What happens is that the plane of exact focus is also tilted and intersects the film plane and lens plane in a line, the Scheimpflug line. If all you are interested in is that plane or aspects of the scene quite close to it, that is enough.

But if you want more in focus, there is another fact you should know. In addition, there is another line (usually) below the lens called the hinge line. There are two additional planes passing through that hinge line, one above the exact focus plane and one below. The region between these additional planes is what is adequately in focus. It is wedge shaped so it is quite narrow close to the lens and widens as you move away from the lens, so it can't be described as simply as in the untilted case. As in the intilted case, its size depends on the f-stop.

As you move the standard back and forth, the plane of exact focus and the whole wedge shaped region between those other planes swings on the hinge line.

I suppose there are lots of people out there making marvelous pictures who don't understand this geometry---probably better than mine, but to me it would be like setting up the camera with both hands tied behind your back and using your teeth to make adjustments.

[Ernest Purdum]

Ideally, when you have the right amount of tilt there would be no focus movement at all between near and far objects. When you have only a little movement as you describe, it tells you that you are pretty close, quite possibly close enough when stopped down.



The procedure I use is neither academic nor mathematical, but it seems to work for me. I stand back a little and try to visualize lines (somebody may write in and say I should say planes) emanating from the near and far objects and from my camera back. I then try to point an imaginary line from my lensboard at the intersection of the earlier two. It is harder when the intersection is far underground, but it still works.



Some practice may help. I have set up targets and played with them.

[Leonard Evens]

I really doubt that anyone, even the most mathematical of us, does much calculation when focusing. There are elaborate formulas which will tell you anything you want to know, but they are too complicated to use in practice. The point is that you don't need much calculation beyond an understanding of the geometry. Merklinger has written extensively on the subject, but unfortunately he may have made it seem more complicated than it is. The large format web site has a reasonable discussion of how you go about it which doesn't require any calculation to speak of. And of course if you are basically just doing the same thing over and over again, you learn quickly what to do without having to think about it. What worked before is likely, with slight modifications, to work again. All of us, to some extent, do that.

I'm afraid that some people are put off by verbal descriptions of the geometry. It is always difficult to describe these things in words, but the geometry itself is fairly simple, and with some study, anyone who is not 3D challenged should be able to visualize it and will probably benefit from doing so.

[Eric Brody]

There's an old rule, for base tilt cameras, that has rarely failed. "Focus on the far, tilt toward the near, re-focus and re-tilt 'til all is clear." As another poster said, there's only one plane of focus, when tilting the lens, that plane is tilted as well. The same goes for the back except in reverse. There are geometric differences between lens tilt and back tilt, but the principle remains the same. No calculations are needed.

[adrian tyler]

well you know that i'm asking because there is always something in the way in the near/middle distance which is vertical and that sets me wondering what is the best aproach. but i was leafing through joel sternfeld's wonderfull book "american prospects" and it's just impossible that these big busy foregrounds (sometimes peopled) are sharp by just stopping down. so it appears to me that front tilt is really quite radical in what it can achieve.

i can understand the geometry aspect of the theory but i really feel more comfortable with what i can see and touch, so really i just wanted to be sure that reducing the length of bellows "movement" between near and far is effectively enlarging dof.

adriantyler.net

[Ralph Barker]

I agree, it's those pesky vertical things that mess things up. ;-) With tilt, DOF essentially becomes a wedge - narrow near the camera and wide far away. So, depending on where the pesky vertical thing falls, you either have to set the plane of sharp focus accordingly, stop down and try to see the dark image on the GG, or some combination.

[Richard Boulware]

I agree with John Cook. Having spend two decades shooting product pictures for Pentax, Honeywell, Redfield, Rollei and many others,....all this formula and mathmatical stuff is just so much nonsense. LOOK AT YOUR GROUND GLASS. Stop the lens down to shooting aperature, check it again with a good magnifier. Yes, you can check your focus on the damned ground glass. That is what it is there for.

Whether it is a swat with your elbow, a fine focus with a loupe, or whatever....screw the formulas, focus with your eyes. Eyes and the ground glass are a perfect combination. Use them! Stop your lens down...with a little practice you can still see sharpness, or lack thereof...and correct. The world of LF photography is still defined by common sense, your eyes, and a good ground glass.......not a damned slide-rule!

Richard Boulware - Denver.

[Leonard Metcalf]

I do it all by feel (WYSIWYG). After some time and practice I just knew where the plans had to go. I used to stand back and look for the intersecting lines (at one point I was using a protractor), but that is now long past. Now my decsions are made under the dark cloth with loupe in hand. Now I have asemetrical movements I find it even easier than before.

My advice is to learn the rules (schemplug & hinge), use them until you understand how they work. And you will soon make the jump to just knowing where to put it all.

I never really understood the hinge rule (trying to understand the book) until I saw these animations. These helped with my understanding. Much easier than the tables he presents. This is the link to the article that have the animations in it.

http://www.trenholm.org/hmmerk/VuCamTxt.pdf