Measuring thread pitch on early Goerz lens

[Fragomeni]

I have an early Goerz stereo lens pair that I’m using for a stereo project. I need to measure the thread pitch on the lenses to have a flange/retaining ring made. I have a couple of thread pitch measuring tools but am unsure what system was used for the lens. Is it just metric? The old British Whitworth scale? Etc. Any help would be appreciated.

 

[AgX]

Metering the pitch is independant of thread system and a banal thing even without thread metering tools. You just have to recalculate the number of windings to the lenght unit of the system of interest, if not metering in that unit from the start.

The other characteristic of a thread system is the shape of the thread flanks. And at smaller thread pitches (as in optics) typically these are not to be established by an amateur other than seeking fit at a thread gauge.


The typical thread gauges over here contain both, metrical and Witworth 55°. With such tool you should be fine for most cases of classic lenses. In both cases you can find both: thread system and pitch.
If you cannot get a nice fit with such, you would need a machinist anyway for the counter-thread. He then would establish the thread you got.

 

[abruzzi]

you might try emailing the people at SK Grimes. They may know offhand--they've been able to tell me on several questions. They have a bunch of shutter flange measurments on their site, but nothing for barrel lenses. I would suspect its just metric given that most (all?) compur and compound shutters were metric, going back to the early days. The inch measurements were on Ilex, Alphax, Betax shutters, which I beleive were all american made.

 

[lecarp]

Instructions for measuring to purchase or have a flange made can be found here.

https://skgrimes.com/services/how-to-measure-threads/

 

[Light Capture]

With only 2-3 turns on your threads gauge might not point to inch or metric thread reliably.

For example: Leica LTM isn't real M39 x1 thread but thread with 39mm diameter with 26tpi. M39 thread works perfectly fine on LTM Leica since thread isn't long enough for discrepancy to show up when mounting the lens. 26tpi equals 0.977tpm.

With that in mind. Thread pitch measurement will likely not be an issue with your lenses. Thread pitch gauge will show if your thread is 55 or 60 degrees (55 degree thread is rare). That will be readily visible.

Major and minor diameters are something that might not be easily measurable since all threads are topped off when made (sharp tips of the threads are flattened).
Same happens with minor diameter. Tools are topped off in order not to make sharp 60 degree corner in the bottom of the thread (minor diameter).

Only accessible tools that will allow precise measurements of actual thread diameter are:
1. Thread pitch gauges (internal and external)
2. Micrometer with thread wires (external - values need to be converted by calculation or by look-up tables)
3. Thread micrometer (external)

There are other methods but not accessible to most people.

Thread measuring wires are available at any metalworking tool supply or on amazon for $15-20.

Most shops are not doing custom sized threads on regular basis and if there is a production run or common sizes are involved go no-go gauge is used.

 

[Ron (Netherlands)]

what is the diameter of the lens (measured on the thread)?

my Dagor 180mm measures 44,42mm. It has an original mounting ring with 24 tpi - but looking at your photo, your lenses seem to have a more coarse thread.

these seem to be yours

 

[AgX]

With that in mind. Thread pitch measurement will likely not be an issue with your lenses. Thread pitch gauge will show if your thread is 55 or 60 degrees (55 degree thread is rare). That will be readily visible.

Good point.
British BSW threads for machines got 55°
American UNC threads for the same got 60°

But for our use the difference in angle seems tolerable.

 

[Fragomeni]

Thanks for the help everyone. I've found a flange that looks as though it may be a match for the one that I already have. Waiting for it to arrive with the hopes that it solves the issue out of the gate. If not, I'll return back to this and just send my existing correct flange out to be copied.

you might try emailing the people at SK Grimes. They may know offhand--they've been able to tell me on several questions. They have a bunch of shutter flange measurments on their site, but nothing for barrel lenses. I would suspect its just metric given that most (all?) compur and compound shutters were metric, going back to the early days. The inch measurements were on Ilex, Alphax, Betax shutters, which I beleive were all american made.

Yea, I've emailed Grimes already and am waiting to hear back. In my experience though they tend not to have data on many of these earlier barrel lenses but we'll see if I get lucky.

Instructions for measuring to purchase or have a flange made can be found here.

https://skgrimes.com/services/how-to-measure-threads/

Yep, those are the instructions I'm using.

what is the diameter of the lens (measured on the thread)?

my Dagor 180mm measures 44,42mm. It has an original mounting ring with 24 tpi - but looking at your photo, your lenses seem to have a more coarse thread.

these seem to be yours
[image]

Ron, yea those are the lenses. I pulled the image I shared off of the original ebay listing. The diameter including the threads reads as 36mm. Interestingly though, one of the flanges that I have has a matching internal diameter, including threads, but it's just a little too big. The flange that I have that is the correct fit (which I'm trying to match) has an internal diameter, including threads, of 35mm and works perfectly.

 

[David Lindquist]

Worth noting that metric pitches weren't always used when one would expect them, nor did thread profiles always adhere to the 55º BSW/BSF or the 60º Unified/ ISO metric profiles.

If you wade through the Compur Werke repair manual here: https://www.suaudeau.eu/memo/rep/Compur-shutter-repair-manual.html

And then look at the specifications of the rim-set No. 2 Compur and No. 3 and No. 4 Compound shutters you'll see the lens mounting threads are 40 threads per inch pitch and are 64º, not 60º. The shutter mounting thread is 29 1/13 threads per inch pitch (never found the reason for this), and the profile is 50º.

Pages are dated September 1962, I expect for the Compounds these specifications may go back to the early 20th century. This reference shows the No. 5 Compound has a shutter mounting thread to the metric standard, 60º with a 1 mm pitch, thread mount threads are as for the No. 3 and No. 4.

David

 

[Ron (Netherlands)]

The diameter including the threads reads as 36mm. Interestingly though, one of the flanges that I have has a matching internal diameter, including threads, but it's just a little too big. The flange that I have that is the correct fit (which I'm trying to match) has an internal diameter, including threads, of 35mm and works perfectly.

This is indeed what you would expect: since the threads are interlocking a measurement of the internal diameter including the threads can not be transposed to the flange and vice versa.

I've had a look into my pile of mounting rings and there is only one that comes near your measurements: diameter 34,55 mm and with very fine thread: tpi 34; so won't fit looking at the coarse threads as seen on the picture of you lenses.

 

[Jojje]

I've encountered thread angle of 45 (or was it 47.5..?) degrees on Mamiya lens. Had to make my own tool to cut a step up ring! This all happened before the internet, of course.
https://www.improwis.com/tables/threads2.webt#metric50deg

 

[AgX]

Thank you for that comprehensive thread etc. details listing.