Minox spy cameras: How's their mechanical heart ticking?

[tjwspm]

The Minox A IIIs, B, BL, and AX use purely mechanical shutter systems to control light for their tiny 8x11mm film. No electronics — just intricate engineering! How do these cameras handle shutter speeds from 1/2 to 1/1000 seconds, plus B and T settings, to achieve perfect exposures?

This question had been nagging at me. Not just out of curiosity about how the designer had managed to achieve this. That too. But what about the Minox cameras where the shutter speeds are incorrect? This is an issue that preoccupies many Minox enthusiasts. If you want to repair it and not just blindly try things out, you need to know what's going on inside the camera.

After a year and a half of reverse engineering, I finally cracked the code of this mechanism. Since my memory isn't very good, I had to write everything down so I wouldn't forget it. Besides, some things only become clear to me when I try to put them into words. I now would like to share the result with you. My article includes many photos and videos —never before seen online or in books — showcasing the system in action. As far as I know, there’s no other technical description like this out there.

I would greatly appreciate your feedback on the clarity and completeness of the article, as well as any further suggestions on other Minox topics – please let me know what you think!

P.S. This is just my hobby — nothing commercial! I write mainly for myself, so that I don't forget the insights I've gained and so that I can share my enthusiasm with everyone who is interested in historical (miniature) cameras.

Click here for the full story:
Trigger Warning: Contains highly technical details that might send tech geeks into excitement!

The Minox exposure system

From the user's perspective, exposure consists of three simple steps: set the exposure time, cock the shutter, and take the picture. All images in this

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[Andreas Thaler]

Thank you for presenting your work as well as your expertise and for the effort you put into this forum.

At the same time, I find it a shame that the interest is only measured by the number of views.

 

[tjwspm]

Thank you.

I had always been unclear about how the set shutter speed is actually transferred to the escapement. My imagination is limited, so I tried to illustrate this with superimposed photos from inside the Minox, namely here:

The shutter speed dial

The shutter speed dial on the Minox is, alongside the shutter release button, the second user interface of the exposure system, which controls the

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[Andreas Thaler]

This is excellent work that deserves attention

 

[Patrick Robert James]

Excellent. The more information that is out there about these little marvels the better.

 

[Andreas Thaler]

Excellent. The more information that is out there about these little marvels the better.

+1!

 

[Crysist]

I had a passing but considerable interest in the Minox cameras when I visited your thread about your site last year. As of a bit over a month ago, I own a Minox B haha! Repair wise, the information you've shared on the Minox is second to none! And you're still making it even better with technical details like this!!

Actually, regarding your guides, I need to go through it to clean the foggy viewfinder mine has. It just seems scary because it requires disassembling quite a lot to get to, including the shutter!

 

[tjwspm]

Thank you! This is the best feedback I could wish for, because my aim is to encourage others to work with the small Minox cameras.

I have never removed the viewfinder, but have the following advice from another Minox enthusiast:

"I broke 2 of them trying, but now I think I can do it safely. The trick is to soak it for a few days in isopropyl alcohol, occasionally taking it out and pressing lightly on the very corner of the glass from the inside (toothpick). The alcohol softens up the adhesive a little, without damaging the plastic or glass coating. Once or twice a day, I pushed a little on the corners, and eventually it started to move.
In my first attempts, I broke the mirrored glass (by not pushing on the very corners where it contacts the front plastic lens corners), and I broke the long corners off the plastic front lens. The mirrored glass in this one had degraded. That’s what was making the viewfinder foggy. On others, there is a buildup of haze between the two lenses, and taking them apart is the only way to clean them.
Have you ever succesfully put a viewfinder assembly (with the metal holder) back into the body? I can’t figure out a way to do it, and I have to remove the viewfinder from the holder so I can hook on the parallax return spring, then glue the plastic finder back in the holder."

As you can see, this is still pioneering work. I've had very little haze in the viewfinder of my Minox cameras so far, so I haven't done anything about it.

 

[Patrick Robert James]

It is real easy to mess up the viewfinder on a Minox. Ask me how I know. They are made of some type of plastic I think. Best to clean them with only water and do so gently. Even better is to buy one that doesn't need to be cleaned. On the upside even if it is a little foggy it doesn't matter. It is only a viewfinder. If anyone has a good way to clean them I'd love to know.

I seem to recall removing the viewfinder on a B years ago. I know it is glued on one side at least. If you can get the glue softened you can take it out but leave the holder in the body. That is what I recall anyway. I just leave them alone these days. I have like 8 or 9 Minox at this point but only a few are 100%. A few need new blades and a couple have issues and are in the repair pile.

 

[tjwspm]

It is real easy to mess up the viewfinder on a Minox. Ask me how I know. They are made of some type of plastic I think. Best to clean them with only water and do so gently. Even better is to buy one that doesn't need to be cleaned. On the upside even if it is a little foggy it doesn't matter. It is only a viewfinder. If anyone has a good way to clean them I'd love to know.

I seem to recall removing the viewfinder on a B years ago. I know it is glued on one side at least. If you can get the glue softened you can take it out but leave the holder in the body. That is what I recall anyway. I just leave them alone these days. I have like 8 or 9 Minox at this point but only a few are 100%. A few need new blades and a couple have issues and are in the repair pile.

Removing the viewfinder is extremely difficult. It is located under the escapement and then under the two blad control levers. I would generally advise against removing the escapement, especially because of a cloudy viewfinder. You can clean the front and back of the viewfinder if you remove the front plate and the back. Even that is time-consuming enough. This photo shows a rare view of the viewfinder with the escapement removed:

The Blade Control

The shutter release button has been pressed and the timing mechanism generates the correct times for opening and closing the shutter based on the preset

moments-of-now.com

 

[Crysist]

It is real easy to mess up the viewfinder on a Minox. Ask me how I know. They are made of some type of plastic I think. Best to clean them with only water and do so gently. Even better is to buy one that doesn't need to be cleaned. On the upside even if it is a little foggy it doesn't matter. It is only a viewfinder. If anyone has a good way to clean them I'd love to know.

I seem to recall removing the viewfinder on a B years ago. I know it is glued on one side at least. If you can get the glue softened you can take it out but leave the holder in the body. That is what I recall anyway. I just leave them alone these days. I have like 8 or 9 Minox at this point but only a few are 100%. A few need new blades and a couple have issues and are in the repair pile.

Removing the viewfinder is extremely difficult. It is located under the escapement and then under the two blad control levers. I would generally advise against removing the escapement, especially because of a cloudy viewfinder. You can clean the front and back of the viewfinder if you remove the front plate and the back. Even that is time-consuming enough. This photo shows a rare view of the viewfinder with the escapement removed:

The Blade Control

The shutter release button has been pressed and the timing mechanism generates the correct times for opening and closing the shutter based on the preset

moments-of-now.com

Duly noted... yeah, it isn't a huge deal to me. Especially with that risk. But my sister's has a far clearer viewfinder and more accurate meter, mine is cleaner on the exterior and mechanically a bit more sound (yes, we became Minox buddies). Only thing on mine that straight up doesn't work is the PC sync socket, do you suppose that's easier to investigate?

 

[Patrick Robert James]

Duly noted... yeah, it isn't a huge deal to me. Especially with that risk. But my sister's has a far clearer viewfinder and more accurate meter, mine is cleaner on the exterior and mechanically a bit more sound (yes, we became Minox buddies). Only thing on mine that straight up doesn't work is the PC sync socket, do you suppose that's easier to investigate?

They used to sell tip conditioners for both male/female sync sockets, but I doubt you could get one anymore. I don't even have one. Should have snagged one a long time ago. But it isn't necessary. Get yourself a sync cable, make sure it is tight over the post then work it back and forth for a while. That should clean up the contacts. The last IIIs I had wouldn't work until I did that for a bit. If it is dirty or tarnished that should fix it. If you take off the end I think the post is exposed but I can't remember.

 

[tjwspm]

I would try it this way too. Maybe spray some contact spray on the sync cable connector. This description of how Minox flash synchronization works might also help:

The Minox enlightenment

Minox AG 1 Flash Unit for Minox A/IIIs Since 1954, Minox A/IIIs had a synchronized flash connection. However, a flash unit had to be purchased from a

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