smieglitz
Member
Does anyone know the difference in standard focal plane depths between sheet film holders and glass plate holders for the 11x14 format? I'm trying to adapt an old 11x14 plate holder to do wetplate collodion ambrotypes in an 11x14 film camera. (I don't assume the difference between 11x14 and other formats will be similar.)
I thought I had it figured out but when I ran a couple tests using enlarging paper at the presumed focal plane (loading the paper from behind with a glass "tablet" backing it and pushing it flat to the corners that hold the surface of the plate at the focal plane) the image appeared unsharp, off by perhaps a couple mm from where I (thought I) had focused on a meter stick. Between my trifocals, the shims I made, the old petzval lens and possible focus shift when using a waterhouse stop, I'm not sure where the error lies.
The plate holder is 1" thick while the film holder is 3/4" thick. The depth to septum in the plate holder is ~29/64" while the t distance in the film holder is ~23/64". So, I guess I need to know the standard thickness of an 11x14 sheet of film and the standard thickness of a photographic glass plate of 11x14 size in order to do the calculation and arrive at the difference in focal plane from the camera's ground glass plane.
Can anyone help me out with the material thicknesses or known difference between the two focal planes?
Thanks very much.
Joe
I thought I had it figured out but when I ran a couple tests using enlarging paper at the presumed focal plane (loading the paper from behind with a glass "tablet" backing it and pushing it flat to the corners that hold the surface of the plate at the focal plane) the image appeared unsharp, off by perhaps a couple mm from where I (thought I) had focused on a meter stick. Between my trifocals, the shims I made, the old petzval lens and possible focus shift when using a waterhouse stop, I'm not sure where the error lies.
The plate holder is 1" thick while the film holder is 3/4" thick. The depth to septum in the plate holder is ~29/64" while the t distance in the film holder is ~23/64". So, I guess I need to know the standard thickness of an 11x14 sheet of film and the standard thickness of a photographic glass plate of 11x14 size in order to do the calculation and arrive at the difference in focal plane from the camera's ground glass plane.
Can anyone help me out with the material thicknesses or known difference between the two focal planes?
Thanks very much.
Joe