Flange Size for C.P. Goerz Am. Opt. Co. K11

[Len Middleton]

Recently acquired from a friend the above lens, but without a flange. My understanding it is a 10-3/4" (about 275mm) Process Dagor and looking forward to giving it a try.

I do have a good (and big) lens clamp (thanks eddie) and I can use that, but would like to get a flange for it, if I can.

I am a little baffled by the dimensions for the flange section of the lens as the outside measurement is 2.26" or about 57.5mm using my digital vernier. There are only about three threads for the flange to engage and the thread pitch gauge unsurprising shows both 24TPI and metric 1.0.

Given the literature at the time shows imperial measurements, did they build the lens using the imperial system, or did they use metric i.e. should the flange be 2-1/4" with 24TPI pitch, or 58mm x 1.0?

I do expect my measurements could be off a little, as I am self taught and could have used a better teacher, but surprised that the imperial dimension slightly exceeds the standard imperial size, even after measuring it multiple times.

Anyone out there have a similar lens and could confirm the dimensions? Or maybe a spare flange in that size they would be willing to part with?

Let me know what you think...

[Henry Ambrose]

24 t.p.i. is probably correct. The thing to watch for is how much the threads are worn from use along with how close they were cut to any standard when the piece was made. For a short length of thread the precise pitch is often not critical. Over the distance of 3 threads either 24 t.p.i. or M 1.0 could fit just fine. What I do when I cut these is to fit to the actual lens. That way I know that its got all the thread engagement available and will hold. So I essentially consider each antique lens to be "one-of-a-kind" to avoid disappointment. But you might find a flange that works just fine, they are out there, you're not the first to mount one of these to a camera.

As to your more general question partly answered above, there are a number of "good enough" fits between metric and American threads, both having 60 degree angles. When the thread engagement is short a thread that is close may be perfectly functional. 24 t.p.i. and M 1.0 is one set that's close.

I'm going to make some more flanges as soon as I finish the current batch of lens boards. Just waiting for everyone's lens board samples right now. Then on to flanges in probably a couple of weeks.