Contax IIa eyepiece: any machinists around here?

[Donald Qualls]

From your second photo, I get 0.25 mm pitch. You can't count the first turn, the thread is covered by the collar,l and your marker line is a little off on the second, but from the first fully visible thread land to the third, is exactly 0.50 mm.

 

[Michel Hardy-Vallée]

From your second photo, I get 0.25 mm pitch. You can't count the first turn, the thread is covered by the collar,l and your marker line is a little off on the second, but from the first fully visible thread land to the third, is exactly 0.50 mm.

That would make sense with metric measurements being divided in halves and quarters rather than thirds.

 

[Donald Qualls]

Today, correctly, metrics should be in integer tenths or hundredths of the listed unit -- but they aren't always, because metric thread standards were established before SI practices were. For instance, standard pitch for M5 is 0.8, but for M8 it's 1.25. And for threads in things like helicoids, camera parts (and gun screws, for that matter) standard pitches go out the window.

 

[Main_Cogg]

Hopefully the threads that I cut will be close enough as my lathe is strictly Imperial. 0.5mm converts to 50.8 tpi and the closest I can get is 52 tpi. If we were working with metal to metal I wouldn't even attempt it, but with plastic to metal over such a short distance, I think it should work ok.

 

[Donald Qualls]

By my count, at 0.25mm pitch, it should be awfully close to 102 tpi. Probably close enough that if there's a little slop in the fit, it'll be find over 3-4 turns.

 

[Dismayed]

This is one reason I like using viewfinders. Depending on the finder it is a clearer view also.

But you can't focus using just an external finder.

 

[markjwyatt]

But you can't focus using just an external finder.

True- focus, then use finder for framing. Either I focus with glasses off, or I do not see full frame while focusing. Sometimes I can see the full frame without pushing in too hard if I try. The o-ring is probably a good way to go.

 

[Dismayed]

True- focus, then use finder for framing. Either I focus with glasses off, or I do not see full frame while focusing. Sometimes I can see the full frame without pushing in too hard if I try. The o-ring is probably a good way to go.

I can only focus with my glasses off if I use a diopter. But then I need to put my glasses on to see the camera settings, so it's easier for me to just keep my glasses on. Getting old isn't for the feint of heart. YMMV.

 

[Michel Hardy-Vallée]

View attachment 249777
I had a little time today so I fired up the ' ol lathe and this is what popped out. They're not perfect, but hopefully they'll be functional. I used the dimensions that Patrick posted but I don't have a Contax to do a test fit, so who knows. What I would like to propose is sending 2 of them to @Michel Hardy-Vallée and 2 to @Patrick Robert James. If you gents would try them and give me your critiques, then I'll make any adjustments and be ready for the onslaught of orders.

Alright, so the two rings you machined arrived today. They are almost a perfect fit: the outside diameter is good and looks good on the eyepiece, but the inside diameter seems to be a little too big. I can get the threads to mate, but they only do so by the tips, so the ring doesn't stay on for long. It can be screwed in, so I think the pitch you used is fine, but it takes only a light push to drop the ring from the eyepiece.

Is there anything specific you would like me to measure or to photograph to help you out with the adjustments? I think we're pretty close.

 

[Patrick Robert James]

Michel, Norm sent me two. One of them fit perfectly on my IIIa.

 

[Main_Cogg]

Michel, if you could measure the OD of the threads on your camera and the ID on the pieces that I sent you, I can compare your numbers to what I measured and I should be able to get it dialed in.

 

[Michel Hardy-Vallée]

Michel, if you could measure the OD of the threads on your camera and the ID on the pieces that I sent you, I can compare your numbers to what I measured and I should be able to get it dialed in.

Doing my very best with Vernier calipers, I end up with 1,00 cm for the Contax, and 0,95-0,96 for the two eyepieces. I think we could shave off another 0,05 cm.

 

[Main_Cogg]

Sorry for the delay, been a busy week. I agree, 0.05 sounds about right, I'll try to get to it this week.

 

[Richard62]

Had the same problem with my Contax IIa and a Kiev 4a. Contax IIa solved with a hole drilled in a rubber tap washer. Kiev 4 solved with a grommet used to protect electrical cable passing through a hole in a metal socket box (about 25mm outside diameter) It was cut in half (width) and surfaced roughed up with a bit of emery cloth. Both were glued to the eyepiece with Bostik.

 

[Main_Cogg]

Finally had some time to work on eyepieces again. Michel, I'll get a couple in the mail to you this week.
@btaylor , if you'll PM me your address I'll send one or two your way.
Anyone else in the U.S. or Canada need one?

 

[Steve York]

Corn plasters are another, not so elegant solution, but they work

 

[Michel Hardy-Vallée]

Now THIS is what I call an intelligent solution! Norm, prepare for the onslaught of orders!

 

[Hatchetman]

I'll buy one!

 

[Main_Cogg]

Michel, I'm glad that it worked out. I have to say, that is a very good looking Contax, not sure my part is up to the same standard.

@Hatchetman , pm me your address, I'm sure we can work something out.

 

[Michel Hardy-Vallée]

Michel, I'm glad that it worked out. I have to say, that is a very good looking Contax, not sure my part is up to the same standard.

@Hatchetman , pm me your address, I'm sure we can work something out.

If you machine one in premium natural rubber from sustainable sources, I'll buy it