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Step 3Automatic Only Lenses
Camera manufacturers eventually began dropping the "AUTO/MAN" switch... after all, the SLRs that needed manual mode were long out of production. In many cameras, the switch was redundant because the camera body provided a "depth-of-field preview" button that works by hitting the pin on the back of the lens. For example, the Zenit Helios 44M-4 58mm f/2 shown has a rear pin, but no switch and is thus automatic only.
These lenses are problematic for DSLRs that don't have a way to press the pin on the rear of the lens. They work fine wide open, but cannot stop down.
The key to making these lenses useful without major surgery is that pin on the back. Basically, you need to keep it depressed all the time to make the lens behave like a manual lens. This can be done any of the following ways (but I recommend #3):
1. Use an adapter that holds the pin down. There are some that have a little built-in ledge for this purpose, but most don't. Aside from adapters with ledges being hard to find, the extra thickness of a ledge could interfere with the mirror box in some DSLRs. As of May 2011, I have found that some M42 lenses cannot focus to infinity because the rear element hits the edge of a slightly too-wide ledge; I found this problem using an M42-NEX adapter with a 50mm f/1.4 SMC Takumar -- this lens worked fine with some other ledged adapters.
2. Cut a tiny piece of metal foil duct tape and use it to hold the pin down. Be careful not to cover the M42 thread nor interfere with the movement of the rear lens group during focus.This method is trivially reversible, but unfortunately is often self-reversing... i.e., the tape becomes loose enough for the pin to pop up part way. This is a good way to quickly test a lens.
3. Use a dab of strong glue to hold the pin down. This is what worked best for my Helios 44M-4. I took a plastic straw and used it to hold the pin down while I placed a tiny drop of glue on the edge of the pin. After holding it in place for 30 seconds, it was easy to leverage the straw free, leaving the pin glued in place. This glue is not trivially reversible, but the glue is only at the tip of the pin, so it is possible to restore the pin to operating condition by either picking the glue off using a needle or opening the rear of the lens and using a temperature change or pushing the pin from the inside to break the glue bond.
4. Perform a little surgery on the lens. Typically, there is a little spring inside the lens that keeps the aperture blades open... you can remove that spring. A variant that works on some lenses involves simply slipping something over the pin on the inside so the pin cannot go through the rear plate, holding it down much as if it had been glued. I don't recommend any surgery unless you've taken apart lenses before -- some lenses have tiny parts inside that can fall out of place.
These lenses are problematic for DSLRs that don't have a way to press the pin on the rear of the lens. They work fine wide open, but cannot stop down.
The key to making these lenses useful without major surgery is that pin on the back. Basically, you need to keep it depressed all the time to make the lens behave like a manual lens. This can be done any of the following ways (but I recommend #3):
1. Use an adapter that holds the pin down. There are some that have a little built-in ledge for this purpose, but most don't. Aside from adapters with ledges being hard to find, the extra thickness of a ledge could interfere with the mirror box in some DSLRs. As of May 2011, I have found that some M42 lenses cannot focus to infinity because the rear element hits the edge of a slightly too-wide ledge; I found this problem using an M42-NEX adapter with a 50mm f/1.4 SMC Takumar -- this lens worked fine with some other ledged adapters.
2. Cut a tiny piece of metal foil duct tape and use it to hold the pin down. Be careful not to cover the M42 thread nor interfere with the movement of the rear lens group during focus.This method is trivially reversible, but unfortunately is often self-reversing... i.e., the tape becomes loose enough for the pin to pop up part way. This is a good way to quickly test a lens.
3. Use a dab of strong glue to hold the pin down. This is what worked best for my Helios 44M-4. I took a plastic straw and used it to hold the pin down while I placed a tiny drop of glue on the edge of the pin. After holding it in place for 30 seconds, it was easy to leverage the straw free, leaving the pin glued in place. This glue is not trivially reversible, but the glue is only at the tip of the pin, so it is possible to restore the pin to operating condition by either picking the glue off using a needle or opening the rear of the lens and using a temperature change or pushing the pin from the inside to break the glue bond.
4. Perform a little surgery on the lens. Typically, there is a little spring inside the lens that keeps the aperture blades open... you can remove that spring. A variant that works on some lenses involves simply slipping something over the pin on the inside so the pin cannot go through the rear plate, holding it down much as if it had been glued. I don't recommend any surgery unless you've taken apart lenses before -- some lenses have tiny parts inside that can fall out of place.
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i did it with all three of my Helios 44m and works very well!
/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.