Focusing On Close Objectsgreenspun.com : LUSENET : Large format photography : One Thread
I was out taking a few closeup shots of flowers today using Polaroid 55 P/N film. My scale of reproduction was between 1:1 and 1:2 with a 90mm lens. Each time I adjusted focus by moving the front focusing knob the flower would either grow smaller or larger with little change in fine focus. I was able to get it in fairly good focus, but it seemed a little soft. I tried f-stops as high as f45. I have a Wisner 4x5 PE. Since I'm new to large format cameras, I figure something is wrong with my technique. Is it common for closeup items to grow while focusing? In some respects this growth makes since because the lens itself is moving while the subject is relatively stationary. However, how does one achieve perfect focus without the subject growth? Is this possible? I guess my question boils down to, "What is the best focusing techique for closeup photography"? I know tilting the lens want help in this situation since the scene is mostly in the vertical; hence, I'm left with f-stops as my primary means of controlling depth. Any suggestions or comments would be greatly appreciated.
Thanks in advance,
-- Thomas W. Earle (firstname.lastname@example.org), May 21, 2000
Focus with the rear standard for close ups. This way the lens will not change in relation to the subject.
-- William Marderness (email@example.com), May 21, 2000.
-- james (firstname.lastname@example.org), May 21, 2000.
One way to ensure sharp focus I find is to project a torch beam through the ground glass and onto the subject, focus by eye so that the image formed by the torch is sharp, then shine the torch on the object and check for critical focus.
-- David Kirk (David_J_Kirk@hotmail.com), May 22, 2000.
At high magnifications it is sometimes better to move the entire camera back and forth instead of moving one standard or the other. With monorail cameras this is easy, with your PE you'll have to adjust both standards simultaneously. Of course, any focusing movement that close to your subject will change the image size. You need to find the right combination of distance/bellows draw to get the framing you like, which is not always that easy. Welcome to the world of LF macro-photography! Regards, ;^D)
-- Doremus Scudder (ScudderLandreth@compuserve.com), May 22, 2000.
You are correct - the magnification is changed anytime the relationship between the lens, film and subject is changed. There is no way around it.
You may experience this when focusing an enlarger. You focus, but your image is the wrong size. You adjust the size, but focus is off. You refocus, but image is wrong size again. So you chase the focus and image size back and forth.
The magnification and angle of view is really dependent on the distance of the lens from the film - not the focal length of the lens. If this is confusing, think of a pinhole camera. The focal length of the lens just determines how well the subject is focused on the film. For example, I can focus at an object at "infinity" with my 90mm lens and note what angle of view is projected on the ground glass. The lens will be approximately 90mm from the glass. Now I can keep the standards at the same location and replace the 90mm with my 215mm lens. The 215mm will attempt to project the same angle of view on the ground glass, because it is in the same position as the 90mm was, but it will be BLUUUURYYYY, and it may not have the coverage to cover the film.
For non-closeup work, the change in magnification is not very apparent, so we often don't notice it. For close-up, it begins to become quite apparent, as you've noted.
-- John H. Henderson (email@example.com), May 23, 2000.