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Disabling 'automatic aperture' on M42 lens
Posted By: Frogonastring, 06-19-2014, 03:49 AM

Hi all,

I've got a lovely Cimko MT 28mm f2.8 M42 lens that is really good and has sharp optics - but rather irritatingly doesn't have an auto/manual switch to allow it to be used on more modern cameras that don't have the lever to depress the aperture pin.

This makes using it on my DSLR a nightmare - f2.8 is lovely to have, but the DOF is too shallow for landscape work, and there's no way of changing the aperture.

I've just had a little fiddle with it and thought I'd share with you my instructions for non-permanently and completely reversibly adjusting old automatic M42 lenses to allow manual aperture control.
This obviously depends on the lens design, but here the fix was quite simple.

This is probably quite a common task - but I thought it might be useful to people who had the same issue/style lenses and wanted to use them to their full capacity on more modern cameras.

There's a Google+ gallery with this information too, here: link!
I've also tried to attach the photos below...

Step 1: The lens as it stands - I've removed the three screws that hold the metal cover around the rear lens element.


Step 2: Remove the metal cover - mine was held fairly well by friction, but using a blob of blue-tac to stick to it to lift it out worked well.


Step 3: Rotate the metal cover by roughly 33, so that the screw holes line up successfully but the indent for the aperture pin is now in the "wrong" place, and so the pin is covered.


Step 4: Screw the metal plate back down, pressing the pin down as you go. I found it worked best doing a few turns of each screw in a circle to keep the pressure even. There's a slight lift in the metal plate on the side where the pin is, but the screws are tight and won't work their way loose.


That's it! The aperture now works manually without having to have a lever to depress that pin.

My only question would be...are there any downsides to keeping the pin depressed like this? is it likely to stretch/damage the springs inside the lens?

Hope this is helpful!

Mark
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06-19-2014, 05:48 AM   #2
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Great!

Other methods include putting the parts back down in the same place (rotating it and still have the holes line up won't work with many), but fitting a little wire sleeve or bit cut from ball point pen to hold the pin down. As I last resort on lenses that are difficult to take apart, you can just glue 'em, that's usually what I do (carefully).
06-19-2014, 06:16 AM   #3
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Thanks! Yes, I think I was fortunate the holes lined up here - it worked one way around, but not the other strangely.

I toyed with the idea of taking the entire mount off (the four screws around the central bit) as apparently this was a series of lenses made for many different mounts with a standard fitting - but for the life of me I couldn't get the screws to turn a little bit. It started to wear the metal heads off the screws - I haven't threaded them, but the screwdriver was damaging the screws more than moving them. I think I'll leave that one well enough alone!

I think my question may have gotten lost at the end:

Is there any downside to leaving this like it permanently? Will it damage the springs on the inside to keep them under tension constantly?
06-19-2014, 06:51 AM   #4
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I'm also for the easy, glue route, but thanks for sharing...

06-19-2014, 08:13 AM   #5
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QuoteOriginally posted by Frogonastring Quote
Is there any downside to leaving this like it permanently? Will it damage the springs on the inside to keep them under tension constantly?
Maybe? Honestly I have only converted those I plan on keeping forever for my own use, and even if I don't most people are just going to do the same thing (or want to) immediately anyway (not too many looking for these lenses wanting their old auto-aperture pin to work on their old film camera) so if you've done it already and made a good job of it, it is probably a selling point.
06-19-2014, 01:22 PM   #6
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I glued mine down but I'll try this the next time around.
06-20-2014, 01:11 AM   #7
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I did this to one of mine. I used the sleeve method by cutting a 5mm piece of nylon from the ink tube of a ball point pen. Left it that way for a year or so then converted it back and sold it none the worse for wear.
Yes the springs are under tension but still within their normal range so there is no over strain and therefore no long term damage I would think.
06-20-2014, 12:17 PM   #8
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Forgive me for asking, but why don't you save yourselves a whole lot of trouble and buy lenses without automatic diaphragm's? In fact, why do you use these old lenses at all? Your Cameras cannot communicate with them, The digital Cameras cannot set the apertures and you are left with an aperture priority exposure system. There is absolutely nothing wrong with that but why buy the latest technology and then take half a dozen steps backwards? I use a Pentax SV from the 1960's and a Pentax SP500 from the 1970's. I also have a DSLR and a Digital Bridge camera but to mix the two systems makes no sense at all. As a matter of interest, my oldest Camera dates from 1901.

06-20-2014, 01:20 PM   #9
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QuoteOriginally posted by Dicknet Quote
why don't you save yourselves a whole lot of trouble and buy lenses without automatic diaphragm's? In fact, why do you use these old lenses at all?


Oooohhhhh, You're in for it now!

Welcome to the forum. I'm sure you'll have a few folks answer your question shortly.
06-20-2014, 01:49 PM   #10
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QuoteOriginally posted by Dicknet Quote
Forgive me for asking, but why don't you save yourselves a whole lot of trouble and buy lenses without automatic diaphragm's? In fact, why do you use these old lenses at all? Your Cameras cannot communicate with them, The digital Cameras cannot set the apertures and you are left with an aperture priority exposure system. There is absolutely nothing wrong with that but why buy the latest technology and then take half a dozen steps backwards? I use a Pentax SV from the 1960's and a Pentax SP500 from the 1970's. I also have a DSLR and a Digital Bridge camera but to mix the two systems makes no sense at all. As a matter of interest, my oldest Camera dates from 1901.
Well, a troll question, but I'll answer anyway. (Once, I won't argue about it, I promise.)

The main answer (for me) is because I want to, and that is all that matters.

Another might be it is the image produced that matters, not the way in which it was. Plenty of these old lenses are mighty fine quality, or have interesting character not to be found on modern lenses, not to mention they can often be had quite cheaply. Is an image better because the camera got to actuate the lever controlling the aperture? Of course not. Did I waste my money on this fantastic technological marvel since I so often put old lenses on it? Putting aside the fact that (for me) part of its technological wizardry is the fact that I can put old lenses on it at all, well how much value I put on something and whether it is worth the money or not is entirely up to me, ain't it?

Bottom-line is your question is kind of like asking, "Why did you marry your wife? Because she's not my type."
06-20-2014, 01:56 PM   #11
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QuoteOriginally posted by JACOBY Quote
I glued mine down but I'll try this the next time around.
I have used aluminum tape on a couple of mine. Works well and is quickly reversible should I want to use them with a Spotmatic.

Also, the aluminum tape works a treat to cover the area that mates with electrical contacts on non-metallic mounts to enable metering.

QuoteOriginally posted by Dicknet Quote
In fact, why do you use these old lenses at all?
Not even going there. I'm sure you'll get plenty of responses.
06-20-2014, 09:35 PM   #12
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@dicknet: When I was a kid I would add new sets to my Lego collection, build the featured model once or twice and then combine the bricks with the older materials and build completely new models - because they were designed to be used that way. For me my camera and lens collection is the same. I enjoy mixing and matching and trying stuff out and occasionally coming up with new looks to old subjects in camera.
06-21-2014, 06:55 AM   #13
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M42 Lenses

I am sorry if I have upset anyone but I have been using M42 lenses for nearly forty years and I know them and understand how they work. You may have gathered that I use Pentax film SLR's as well as Digital and it beats me why you are prepared to use these Lenses on a Digital SLR together with all the problems that go with them but as you say, this is your concern, not mine.
However, i will say this. Don't assume that because an M42 lens is old then it must be good Quality. Most will be but there is also some rubbish out there so check them carefully especially for Fungus.
Once again, please accept my apologies for any offence that I may have caused.
06-21-2014, 07:19 AM   #14
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Try this? It looks like infinity should be retained and the stop down pin depressed only when the lens is in the adapter.
General Brand Pentax-K Body to Universal Lens Adapter ABPKS B&H
06-21-2014, 04:43 PM   #15
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"Most will be"

No doubt you will have checked out the very large number of interesting and high quality images on the Takumar and K mount threads.
Many of those images will have been made on combinations of the old lenses with digital bodies.
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