Bag Bellows DIYgreenspun.com : LUSENET : Large format photography : One Thread
Planning to build a bag bellows for my monorail 4x5 camera. How important is the inside surface? Does a slight sheen to the fabric cause concern? I got thinking about all the space inside the view camera bellows and compared that to the lenghts medium format camera makers go to by adding baffles in the body. Is there any concern with a view camera about similar internal reflections? Do bag bellows inherently produce more flare than a pleated bellows?
-- Dave Schneider (firstname.lastname@example.org), April 17, 2001
Dave: I don't pretend for one minute to be a camera engineer, but I feel that any reflective surface in the path of the optical image can be degrading. With a bag bellows, the majority of the bag will be on the outer edge of the light path, but where it meets the camera body it can be quite close to the light cone. The effect may be slight, but can cause density problems at the edges of the film. Ansel Adams wrote about internal bellows reflections with his Ansco view camera due to the small size of the bellows. I have experienced the same problems with my own Ansco view camera. A good lens shade is a must. With a bag bellows and a lens with a large circle of coverage, I think you might have problems with the reflections from a shiny surface.
-- Doug Paramore (email@example.com), April 17, 2001.
See the recent thread on bellows materials. You probably want to use a similar two-layer construction as with regular bellows, but, of course, without the stiffeners. You want a dark, matte, lightproof material on the inside like the shutter curtain material discussed.
-- John H. Henderson (firstname.lastname@example.org), April 17, 2001.
Dave, I made a bag bellows for the Bender 4x5 I started with, it was an option with the kit. As I recall, the material had a slight sheen to it, but it never caused a problem. One reason may be that bag bellows are used with wide angle lenses with short focal lengths. When these lenses are focused for average distances the rear elements are quite close to the ground glass and the image circle is not that much larger than the camera back, so I think there is less light bouncing around in the first place. You might try to contact Bender to see if he would sell you some of his material. It was a fairly easy project to construct.
-- David Rose (DERose@msn.com), April 20, 2001.