Large image circle cause fogging?greenspun.com : LUSENET : Large format photography : One Thread
Is it possible that if you use a lens with an image circle far far in excess of requirments that the light bouncing around inside the bellows could cause fogging?
I wouldn't have thought so, but a friend of mine who shoots LF suggested that it _might_ happen.
-- Chris Bitmead (email@example.com), August 12, 1998
Not fogging, but this might reduce contrast. The bellows are black inside, so for that to happen, the area imaged outside of the image would have to be quite bright. In those situations, it is a good idea to cut the image circle by using a compendium shade. To be safe, you could always use one on every shot.
-- Quang-Tuan Luong (firstname.lastname@example.org), August 12, 1998.
This is not "fog," it is internal flare from reflections off the bellows or other internal components of the camera body. I have had this problem with the 450 mm Nikkor on a 4 x 5 Cambo SC II. Remember this Nikkor lens will cover 11 x 14 at infinity. I have used the 420 mm Rodenstock without this flare problem as it has a smaller image circle.
The relatively small inside size of the Cambo 4 x 5 SC II bellows and the mounting frames are the most likely cause. A larger camera bellows with larger frames lke the Arca-Swiss or Linhof Kardan will not have as much problem.
The other issue is the actual refelctance or sheen of the bellows lining. Check to see if its internal surface is reflective.
If you doubt the reality of this issue, make two identical exposures, using the same lens, changing between the square and bag bellows - a 210 is ideal for this test. The film made with the bag bellows will have less flare density than the one made with the square bellows. See also "View Camera Technique" by Leslie Stroebel. If you are not sure, a Polaroid test will confirm your suspicions!
-- Bob Boettcher (email@example.com), August 24, 1998.
I concur that the internal flare from internal reflections in the camera can be a serious problem with ANY lens that covers more than the format.
Ideally all of this flare could be eliminated if a perfect lenshood was used to eliminate any excess light from hitting the bellows.
From a practical standpoint, a good square or rectangular lenshood which is positioned for maximum effect (shading) can reduce this flare to a minimum. In that case the excess image producing ability of the long focus lenses is "tamed" for the format being used.
-- Bob Eskridge (firstname.lastname@example.org), August 24, 1998.