Unusual Yet General Technique Questiongreenspun.com : LUSENET : Large format photography : One Thread
I'm hoping some of you accomplished LFers can sort out a disagreement I have with a fellow photographer that goes to the basic foundation of large-format photography. It's kind of hard to explain, so forgive me if this sounds a bit convoluted and long-winded. Here goes. . .
My contention is that LF depth of field technique is basically the same as that which I have used with my Mamiya RB67 (pick a composition, select an aperture that'll render everything I want in focus), except that with my LF I can use movements to "enhance" or "alter" my DOF on images that need more depth than simple aperture selection can attain. I know how the Scheimpflug principle works. My friend, on the other hand, says that I should always use movements first, not only in terms of order of application in the field, but from the very start of the conceptual process. Here's an example that I used on him to stress my point, and his reply: I'm shooting two cottonwood trees, one is 75 feet away, the other is 100 feet away. I know that with my 210mm lens, if I focus on the closest tree and use a relatively small aperture, say f32, that everything from that tree to the horizon will be within the zone of focus. (Assuming, for argument's sake, that the tree at 75 feet isn't quite at infinity, but close.) Or I could even focus a little beyond the first tree and let some 'front-side' DOF bring it into focus. Therefore, in either case, I wouldn't even need to consider movements.
My friend contends that instead of focusing on the closer tree and stopping down, I should focus on the closer tree and then use tilt to bring the farther tree into focus. Then I can stop the lens down to increase my chances further. My problem with that scenario is that the tilt will not increase the DOF unto itself, rather it will only change the *plane* of focus. I would therefore have to worry not about being in focus from one tree to another, but instead, from the bottom of the tree to some point *above* my new plane of focus.
Furthermore, he argues that he can get much more DOF out of a 210mm lens on his 35mm camera than a 210mm on LF. MY argument is that both lenses give exactly the same DOF (DOF is DOF is DOF, etc.), but the LF lens covers a wider angle of view, so objects that aren't even in the frame of his 35mm shot will need to be reckoned with in LF. I am certain that if we shot in the exact same direction with the same focal length (him on 35mm, me on LF), I could crop a 24mm x 36mm frame out of my 4x5" shot, lay it side by side with his 35mm image, and the two would be exactly the same (discounting slight variations in lens quality and other such peripheral factors).
-- Todd Caudle (email@example.com), December 24, 1999
You are definitely right on the second point. In fact, since 35mm needs a smaller circle of confusion (one of the factors in the DOF equation) than 4x5, DOF for the same length lens at the same aperture can actually be said to be greater for the larger format. As you say, if you looked at a cropped 4x5 neg, it would look the same as the 35mm. On the first point, given the specific example you use, like you I would probably stop down and forget about tilts for the reasons you give. Tilting probably doesn't gain you anything in that situation (swings might if the trees were the only thing you wanted in focus, but that's an unlikely scenario). But I don't agree that you should choose either movements or stopping down as the first option in all situations, it depends on the nature of the subject. If I were taking a picture of the ground at the Bonneville Salt Flats, I'd definitely think of tilting first.
-- Chris Patti (firstname.lastname@example.org), December 24, 1999.
There's no doubt about the fact that tilting in the tree scenario would result in out of focus tree tops (or bottoms, depending on which way you tilt). Many times, in LF photography, the temptation to use more movement than is truly needed results in creating more problems than it solves. After a bit of practice there is a certain amount of intuition involved in sizing up a particular situation, but as a rule, I like to measure the depth of field I need for a scene by first focusing on the nearest and then the furthest object I want in focus. By observing the spread, in millimeters, on my focus bed, I can calculate what aperture will render the depth of field I need to bring everything into acceptable focus. I then place the front standard precisely in between the two extremes and shoot. Sometimes the spread is very little, maybe one or one and a half millimeters. When this is the case, I don't bother with movements unless improvement is blatantly obvious, such as the example one other contributor gave of shooting the salt flats. Here, there is no doubt that tilting back will reduce the spread at little or no cost in sharpness to other scene elements. That will give me more choice of aperture to use. If it's a more complicated scene with foreground objects that rise high into the frame, there's no point going through the exercise if the spread is manageable. I just calculate the needed aperture (actually I have a cheat sheet close by) and shoot. If the spread is too great, say five or six millimeters, then I have to play a bit. Sometimes I can improve the situation, other times I make it worse. It all depends on the scene. Occasionally, I have to do a compound Scheimpflug, tilt and swing. It's a little more time consuming, but sometimes worth the trouble. There is an excellent article in a past PhotoTechniques magazine on the technique I described. Forgive me but I forget the issue. It was a couple of years ago, I believe. Perhaps another adherent to this procedure has the issue number and will post it. Good luck
-- Robert A. Zeichner (email@example.com), December 24, 1999.
Most likely, you won't be able to gain DOF by tilting unless the trees are very short.
-- Carlos Co (firstname.lastname@example.org), December 26, 1999.
What many people don't realize about swings and tilts is that the world is rarely that two dimensional. I find I use a tilt or swing about 10% of the time, even with many close images in my portfolio. I commonly use f32 or f45, however. There always seems to be something sticking out the top or bottom, or sides of a tilt or swing image. Sometimes, you can use about half the movement, and a small stop to boot. This gives a nice combination for depth, without sending the oddball parts out of focus. I find I rarely use a movement for focus control unless the obect is within a few feet of the lens.
-- Chris Wray (email@example.com), December 26, 1999.
On the first point, I agree w/ Robert. You'll end up w/ out of focus tree tops. If you use tilt, I think you have to put the J point either deep underground or high in the air using a small amount of tilt. You can play tricks w/ the standards to move the J point behind the camera and in the air or below ground, but it certainly complicates the shot.
On point two, theoretically, both 35mm and 4x5 lenses w/ the same focal length and CoC should have the same DOF, BUT in a Dec 20,1999 post (http://photo.net/bboard/q-and-a-fetch-msg.tcl?msg_id=000hMf) on the medium format digest by Kornelius Fleischer of Carl Zeiss says, "In general the Biogon is less prone to resolution drop with defocussing compared to typical SLR lenses of similar focal length. This means: it has more depth of field than other lenses of different optical design. (It is not widely known amongst photographers, that lenses with the same focal length can have different depths of field. Cinematographers have been aware of this fact for more than half a century. The realties of optics are far more complex than the simple equations used for calculating depth of field scales and tables. Those are just funny toys or rough "guesstimates" with little accuracy and meaning in the real world.)." So I guess the conclusion on the second point is 'maybe.' :-)
-- James Chow (firstname.lastname@example.org), December 26, 1999.
As a general rule with LF, it is worth considering what plane you want entirely in focus, and then consider how much in front and behind you want 'reasonably' in focus.
When my subjects are trees, I generally want a whole tree to be in focus, so I usually have a vertical back.
For a 210mm lens used on 35mm or 5x4, at a given aperture, the DOF will be identical on the film. However, for a given print size, the 5x4 will need less enlargement, so will have more DOF.
However, with modern sharp lenses and film, and lack of grain in large formats, my senses are much more critical and I don't generally like to rely on DOF in LF.
-- Alan Gibson (Alan.Gibson@technologist.com), December 28, 1999.
from above post: "For a 210mm lens used on 35mm or 5x4, at a given aperture, the DOF will be identical on the film. However, for a given print size, the 5x4 will need less enlargement, so will have more DOF. "
Actually, if both 35mm and 4x5 are using the same focal length (210mm in this example), then to duplicate the same 24x36mm image area in the 35mm would require the exact same enlargement of that portion of the 4x5.
-- Todd Caudle (email@example.com), December 28, 1999.
Hi Todd. I may be missing something here, but are you sure your friend didn't mean to use a swing (not tilt) to bring both trees (trunks, anyway) into sharp focus? That is, the plane of focus would remain vertical but go through both tree trunks.
-- Bill C (firstname.lastname@example.org), December 28, 1999.
Hi Bill. Actually, to illustrate my difference of opinion with my friend even further, he says he uses movements in almost every shot he takes. For instance, one shot of his that I like very much is from a pretty good distance from a lake, with mountain peaks in the background and not much of anything real close in the foreground. When I see the shot, I see a shot that's at or near infinity all the way. So I asked him what he would do in that situation and he said he used tilt. Sure, if I was shooting at the salt flats in Death Valley (which I will be when I attend Ron Wisner's workshop in late- January), I would know right from the start that I want to use either front forward tilt or rear backward tilt. But in his example with the lake and mountains, I'd simply focus at some point well into the scene and stop the lens down to f22 or f32. I am nearly convinced that there's something very elemental to LF photography that is going right past him.
-- Todd Caudle (email@example.com), December 29, 1999.
well the latest example you've given might prove overkill on both counts...you might have enough dof at f8 even with the 210 if the scene begins and ends near infinity depending on a lot of other things that i can't see and haven't been told.
-- trib (firstname.lastname@example.org), December 30, 1999.