Contax IIa eyepiece: any machinists around here?

Michel Hardy-Vallée · Jul 4, 2020

I was a bit careless the other day and scratched my glasses against that darned threaded eyepiece on my Contax IIa. Luckily, my glasses were under warranty, but it got me searching high and low for something.

Based on existing literature, the thread would have been used to mount diopter lenses (Zeiss code 901), and not much else. They cannot be found nowadays, and there doesn't seem to be other accessories for it.

So I could just get something soft and mushy to glue around the eyepiece, but since the only thing needed to protect the glasses would be a threaded ring made of something soft with no sharp edges, I was thinking: couldn't they just be machined?

Once the thread pitch is found (I suspect it's metric), a few cuts to make the surface of the ring curved, and we're done. Anybody interested?

gorbas · Jul 4, 2020

I was thinking about similar issue with USSR rangefinders windows. Looks like nobody wore glasses back then? What do you think about applying a few coats of liquid electrical insulation on it. It comes in different colours, it's thick and will protect glasses.

Donald Qualls · Jul 4, 2020

gorbas said:
I was thinking about similar issue with USSR rangefinders windows. Looks like nobody wore glasses back then?

Lots of folks wore glasses back then. However, glasses back then had lenses made of actual glass, which is harder than the brass eyepiece surround on these cameras and didn't have coatings that would scratch -- in fact, a soft ring would increase the risk, as it might catch and hold particles of grit (that *are* harder than the glass in your spectacle lenses) and drag them across the surface of the glasses.

I have an anti-scratch coating on my glasses, and so far haven't had a problem with my Kiev 4 eyepiece. Perhaps I'm just lucky, though the 4 seemingly changed the eyepiece design to eliminate the exposed threaded end.

Michel Hardy-Vallée · Jul 4, 2020

gorbas said:
liquid electrical insulation on it.

I had to Google it, because I never knew these words could go together... Sounds like an idea, but it is ultimately easy to remove if I mess up?

Donald, the Contax IIa appears to have a steel eyepiece. So that's why I'm thinking about a solid plastic ring, rather than something foamy.

Plastic is soft, deformable, has no sharp edges, and can be machined to reasonable tolerances, depending on the actual material used.

btaylor · Jul 4, 2020

Seems to me gluing a rubber o-ring around the offending piece would do the trick. I haven’t gotten around to it yet on my Contax IIa. It is a bit of a hassle, but because I would have to push in so much with my glasses on to see the outer area of the viewfinder I just leave my glasses on and focus the rangefinder with what I can see, then move my glasses up and push my eye in to see the framing. Yea everything is blurry but I already know what I want in the frame so it works. I have boxes of o-rings, I should try gluing one on one of these days.

btaylor · Jul 4, 2020

Michel Hardy-Vallée said:
So that's why I'm thinking about a solid plastic ring,

If someone made one I would definitely buy a copy

Frank53 · Jul 4, 2020

I bought a voigtlander diopter lens in my strength and glued it to the finder of my III a.
Not the most elegant solution, but it works.
Regards,
Frank

markjwyatt · Jul 4, 2020

btaylor said:
Seems to me gluing a rubber o-ring around the offending piece would do the trick. I haven’t gotten around to it yet on my Contax IIa. It is a bit of a hassle, but because I would have to push in so much with my glasses on to see the outer area of the viewfinder I just leave my glasses on and focus the rangefinder with what I can see, then move my glasses up and push my eye in to see the framing. Yea everything is blurry but I already know what I want in the frame so it works. I have boxes of o-rings, I should try gluing one on one of these days.

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

John Koehrer · Jul 4, 2020

There were pads for corns on toes that were round with a hole in the center. Typically
available in drug stores. Dr. Sholls corn remover seems to still around probably other brands too.

Donald Qualls · Jul 4, 2020

John Koehrer said:
There were pads for corns on toes that were round with a hole in the center. Typically
available in drug stores. Dr. Sholls corn remover seems to still around probably other brands too.

I don't think I'd recommend those -- the sticky side is impregnated with salycilic acid (that's what removes the corn), which is likely to corrode the metal on the camera eyepiece.

gorbas · Jul 4, 2020

Sounds like an idea, but it is ultimately easy to remove if I mess up?
Well, my supply of liquid electrical insulation dried up, so I have to buy another can, but that was my plan B for eyepiece of Kiev 4. For now I have piece of camera tape with round hole made with leather belt punch tool. It works too. I simply refuse to wear plastic lenses in my glasses, pure glass only. It's getting harder and harder to convince opticians to deal with real glass but I'm firm with my requests.

Main_Cogg · Jul 4, 2020

If you can determine the pitch, PM me a sketch with all the dimensions and I'll give it a shot. No guarantees, I've never cut internal threads that fine in plastic.

Patrick Robert James · Jul 4, 2020

My IIIa has a little plastic piece that is threaded on.

You don't have to thread it. A compression fit would work probably. If the material was softer than the brass of the eyepiece it would form it's own threads if you screwed it on.

I have a leather donut that Aki-Asahi sells for the Leica. That viewfinder does damage too...

I suppose you just need something softer than your glasses. A thick piece of leather with a hole punched in it would work. Or a rubber faucet washer. I've seen those that would be the right shape to fit. You'd just have to find the right one. I've seen people do things with Sugru too. Sorry, don't know how you spell that...

guangong · Jul 5, 2020

The easiest solution with best all round results would be to replace spectacles with contact lenses. No fussing with viewfinder window and just better vision.

StepheKoontz · Jul 5, 2020

This thread got me looking, I stumbled across a single copy of an adapter for these that uses the larger, commonly available nikon round diopters. No idea who made these or if was a custom one off thing.

JPD · Jul 5, 2020

Cosina should revive the Voigtländer Kontur finder, and make a new version with attachable framelines for different focal lengths. Then you would only use the camera viewfinder for focusing. You wouldn't need to put the viewfinder against your eyeglasses to view the whole image, but only close enough to see the rangefinder spot for focusing. Then composing with the Kontur. The new Kontur could have a dial for parallax compensation.

http://camera-wiki.org/wiki/Kontur

Donald Qualls · Jul 5, 2020

I bought a Leitz auxiliary finder for my Kiev, covers 35-135mm and has parallax compensation (set the distance on a lever). Much bigger eyepiece than the Kiev, or than the Argus accessory finder I bought first.

Michel Hardy-Vallée · Jul 5, 2020

Main_Cogg said:
If you can determine the pitch, PM me a sketch with all the dimensions and I'll give it a shot. No guarantees, I've never cut internal threads that fine in plastic.

What would be the best way to determine pitch? I have an el-cheapo Vernier caliper I could use to get close.

Michel Hardy-Vallée · Jul 5, 2020

Patrick Robert James said:
My IIIa has a little plastic piece that is threaded on.

Can you make a photo of this, just to see what it looks like?

Michel Hardy-Vallée · Jul 5, 2020

So I don't have tools precise enough, but the thread pitch is clearly below 1mm. It's about the thickness of a Post-it note. Maybe I could get a set of feeler gauges to check.

Main_Cogg · Jul 5, 2020

If your calipers have the secondary anvils for measuring inside dimensions you should be in good shape. You'll need to align the tips of the anvils with the peaks of the threads. It may be a bit easier to measure the distance between more than two threads, then you'll just have to divide the distance by the number of threads. Feeler gauges will work as well, anything to get the distance from peak to peak. If that's what you've done with the Post it note, that would put the pitch in the neighborhood of .1mm. That is an extremely fine thread. If it is that fine, we can probably get away with just cutting the inside diameter to what should be the minor diameter ( the theoretical minor diameter can be determined mathematically from the outside diameter and the thread pitch) and letting the threads form as you screw it on.
Hope this helps.

Patrick Robert James · Jul 5, 2020

Here is the image of the plastic piece Michel.

If you want to make a replica, I got out my handy Fowler digital calipers and the diameter of the male thread measures 9.89mm repeatedly. It is a .5mm pitch. The male thread extends 1.5mm from the body. The plastic piece is about 3mm deep, so deeper than it needs to be. I think 2mm depth would be more than enough. I'd make it thicker too so it doesn't crack if it takes a bump.

I am glad you asked me to photograph it Michel because when I got it out the plastic piece was loose so I could have lost it. I guess not all good deeds go punished.....

If you make one I'd appreciate one too. Wish I had a lathe. It would be a piece of cake to pound out a dozen of them.

Hope that helps!

John Will · Jul 6, 2020

Simple cheap solution.

Pack of rubber O rings from $2 shop.

Select best fit (from this pack, lower left) and attach with rubber cement.

Main_Cogg · Jul 6, 2020

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.

Michel Hardy-Vallée · Jul 7, 2020

Main_Cogg said:
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.

Hey, you've been quick! I'll PM you my address. Meanwhile, here's what I did: using my USB microscope, a scale, and the Analyse tool in PS, I measured visually the thread pitch. I have something like 0,3 mm between each thread; the whole threaded area is 1,25 mm. The entire eyepiece is 1,75mm thick.

Contax IIa eyepiece: any machinists around here?

Michel Hardy-Vallée

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gorbas

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btaylor

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