Focus Delimmagreenspun.com : LUSENET : Large format photography : One Thread
While out making photographs in the back country last weekend, I ran into a situation that caused me a considerable amount of frustration. I was shooting at the top of a cliff above a mountain lake with an interesting rock in front of me about five feet away and at the bottom of the 75-100 ft cliff I could see some fallen dead trees near the lake and in the distance a mountain range. I could get the rock and the distance to focus on the ground glass but had one HELL of a time to get the fallen trees at the bottom of the cliff into clarity. After about 10 minutes of failed attempts I realized that I had two planes to focus and the shot was probably doomed from the start. I would appreciate any similar experiences and ways that you accomplished sharpness in the final results. I was shooting with a 180 mm lens on a 5x7 camera.
Many thanks in advance.
-- Michael Kadillak (firstname.lastname@example.org), June 25, 2001
Tilt & stop down for depth of field. There are, however, situations where you can't get it all in focus. For example, if the near and far are very close in the image vs. at the edges.
There are split filters to help in this situation.
The other option is a pin-hole lens. Overall, not as sharp as glass optics, but equally sharp at all distances (more or less).
-- Charlie Strack (email@example.com), June 25, 2001.
I asked a somewhat similar question recently and you might want to refer to the archives to see if any of the more detailed answers will help. I basically got three opinions. 1. Tilt and stop down (sounds like you may need to stop own a lot in a situation like this), which is what I tend to do. 2. Use no tilt at all. 3. Certain situations are beyond the limits of the camera for decent resolution - recompose. There is a similar example of this in John Fielder’s "Photography and the Art of Seeing", where he applies forward tilt and stop down method. The question remains with me, how much to stop down and still have optimum resolution? (I'm not sure where a split filter would address this).
-- Roger Rouch (firstname.lastname@example.org), June 25, 2001.
Tilt UP! That aims the wedge of sharpness DOWN into your scene. Typically (if there is such a thing) you and your camera are on the ground trying to focus on things along the ground and sticking out of the ground like nearby rocks or trees and distant peaks. So you tilt down and the wedge of sharpness comes up out of the ground under your tripod and hopefully is wide enough to scoop up the tall things in the foreground as well as the base of the peaks. Your situation, which is not uncommon in my experience, is the reverse in that you're looking down. So tilt up. The wedge of sharpness then originates above your head and the dilemma is to encompass the short things in the foreground with tall things (peaks in this case) in the background.
-- John Hennessy (email@example.com), June 25, 2001.
John has hit the nail on the head with his discussion of the wedge. If you would like a more in-depth explanation of this concept, go to http://fox.nstn.ca/~hmmerk/. At this website, Merklinger goes into the mathematical details involved in working with tilts, swings, and f/stops to control depth of field. There are some good active examples of what happens.
-- Ken Burns (firstname.lastname@example.org), June 26, 2001.
Alternatively, get yourself a Rodenstock depth of field/schiempflug calculator. I have used this little gizmo for a while and has made my life much easier. As John stated the tilt should be UP and is easily seen in the calculator where it asks you for the angle from near to far plane. If horizontal is 0 then any neg angles should have you tilting up.
-- Jorge Gasteazoro (email@example.com), June 26, 2001.
I believe you have identified your problem in the body of your question. It has to do with how far away various objects are from the re-established plane of focus, which you did when you tilted the camera back. Without any movements, the most distant object from the film plane was the mountain in the background, the nearest being the rock. When you focus on an object (or imaginary point) that is half the distance from the mountain as it is from the rock, you can calculate the aperture needed to achieve the needed depth of field and shoot. The problem is you probably won't have an aperture small enough to do this. If you did, you wouldn't be satisfied with resultant sharpness due to diffraction artifacts. The alternative would be to re-establish a focus plane that would reduce the delta or difference in position of the front standard to bring near and far in focus. If you were to pick a point roughly 1/3 down the top of the mountain and use it and a similar point 1/3 down from the top of the rock as your reference points for establishing a new plane of focus, you will notice that optically, the most distant object in the scene are those confounded trees. They should be within an acceptable range in which you can achieve decent focus by using an appropriate aperture. Why the 1/3 down the mountain business? You have twice the depth of field behind the focus plane as in front. Behind are those trees, in front are the tops of the rock and mountain. This is a whole lot easier to diagram than explain in words, but if you think about it a bit, it may make sense. I hope this helps in some small way.
-- Robert A. Zeichner (firstname.lastname@example.org), June 28, 2001.