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Picture of M42 Lens Aperture Control on Modern DSLRs
The M42 "universal screw thread" lens mount was used on film cameras from Pentax, Praktica, and others for decades...  so a lot of great old lenses are available at modest prices. A lot of people are buying adapters (usually $5 to $30) that allow M42 lenses to be used on modern DSLRs made by Canon, Olympus, Pentax, Sony, etc.

Physically mounting an M42 lens on your DSLR is easy with an appropriate adapter, and of course the lens will have to be focused manually, but there is also a little matter of how one controls the lens aperture. The aperture is the thing shown in the photo; a diaphragm consisting of a set of blades that allow the amount of light passing through the lens to be reduced to the desired level, which also allows a controlled increase in the depth of field.

There are three basic types of M42 aperture controls , listed here in chronological order. The catch is that all three types can have no response to turning the obviously marked aperture ring -- without being broken. This little instructable is about how to make aperture control (f/ number setting) on each of these types of lenses work on your DSLR.


 
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EboneezerG made it!2 months ago

Very interesting piece. It certainly got me thinking. However I respectfully think this is setting about the task in a manner which is fundamentally flawed. Why buy an adpator if you are still going to hack the lens anyway. It really is like buying a proverbial dog and barking yourself. Surely a better approach would be to hack the adaptor instead?

Firstly adaptors are simple and cheap. If you break it, then it is easily replaced. Whereas lenses are more expensive and becoming increasingly rarer with the relentless march of time. And modding the adaptor is actually really simple:-

Most adaptors come apart. The 42mm screw part is retained by three grub screws. loosen these grub screws (no need to remove them completely) and remove the threaded part. Measure the adaptor's inside diameter - i.e the diameter of the bit that the threaded part fits into. In my case using the Fotga adaptor, this was 51.5mm.

Find a piece of thin flexible plastic. between 0.5mm and 1.0 mm thick. Bit of left over blister pack would probably do. Cut a circle 51 mm in diameter. Measure the centre of the back of your lens. Probably a bit under 34mm. So cut hole on plastic disk with trimming knife 34mm in diameter. This effectively makes a washer 51mm OD by 34mm ID. Clean off any swarf. Place washer in adaptor. Refit threaded part on top of home-made washer. Tighten grub-screws. Et voila! Cheap, clean, reversible and no damage to the lens!

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HankD1 EboneezerG2 months ago

This is simply a way to make the ledged adapter (option 1 in Step 3), which you can easily just buy at no higher cost than the un-ledged version -- they're no longer hard to find (they were when I wrote this Instructable). I guess yours is nicer in that the plastic is flexible, which a metal edge surely isn't.

The correct adapter hack would be to have a moving piece that depresses the pin on demand. That's actually not hard to do now that I've been designing and 3D printing my own adapters for a couple of years. Maybe it is time for me to update this Instructable...?

Mascimo4 years ago
Thanks for the micro surgery tip. I have been using my helios 44m-2 always wide open, and couls only think of ways to hold the pin from the outside. Now what I did was to remove just the four screws the hold the first plate of the lens, gaining acces the the pin from inside. I rolled up a 2mm broad piece of tape on it and voila, it worked perfect...
Hitman1014 years ago
Thanks a bunch for this tutorial. I recently purchased a MIR 1B m42 lens for my DSLR and was a bit confused after finding out it had a preset type aperture control. This tutorial explain very clearly how to use it. Thanks again!
plokko5 years ago
to mod an automatic lens(without M switch)simply open the back of the lens and stick 3mm of rubber(i used a piece of silicone tube);
i did it with all three of my Helios 44m and works very well!
ProfHankD (author)  plokko5 years ago
The minor surgery you suggest is known to work for auto Helios 44 lenses and at least some other M42 lenses:

/forum.manualfocus.org/viewtopic.php?id=913
www.pentaxforums.com/forums/pentax-slr-lens-discussion/51749-m42-auto-only-lens-modification.html


Unfortunately, some lenses have small parts that can fall out of place if the wrong screws are removed....

Incidentally, opening the back of the lens as you discuss and pushing the pin is one of the surest ways to break the glue bond to undo the method I discussed.
it's true but if you use caution and precision all the m42 lens are easy to open;i have a lot of them and i've opened most of them in all their parts for repair without problems.