View Full Version : Does anyone have a Dallmeyer-Bergheim lens?

23-Feb-2011, 08:30
I'm attempting to build a copy of the famous Dallmeyer-Bergheim soft focus lens and it would really help to have some measurements from an actual lens. Specifically, I'm interested in:

--The focal length and diameter of the positive plano-convex element (even if this info is all I can get, it would be helpful)

--The diameter of the rear plano-concave element

--The distance between the elements at the maximum focal length of the lens

--The distance between the elements at the minimum focal length of the lens

--The distance of the aperture from the front element

--Any estimates of coverage at the minimum and maximum focal lengths

Also, does anyone have the simple telephoto formula for how the distance between the elements affects the focal length of the lens? Thanks.

Steven Tribe
23-Feb-2011, 09:32
You will also need the midpoint thickness of the lens (callipers) and the refractive indices!
An interesting project and quite feasible, I think.

23-Feb-2011, 09:58
Steven-- Doesn't the focal length, diameter, and refractive index determine the curvature (and thus midpoint thickness)? I think it would be enough to have the diameter and focal length and use a standard crown glass like BK7. I'm assuming (maybe wrongly?) the most important parameters are the diameter and power of the elements. The D-B is a simple uncorrected telephoto design. My preference is finding surplus elements or buying new stocked elements--rather than custom grinding.

Steven Tribe
23-Feb-2011, 10:41
Certainly some of the 1900-1920 tele attachments would be useful as a mounting barrel with plenty of adjustment possible. They have little use these days and no buyers (speaking from experience). The D.B is a pretty wide item, though.