Originally posted by Ropuchy
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Thanks for all the input!
It looks like you've had plenty of help already, but I'll add my two cents.
I use three different M42 adapters for my Canon DSLR. None of them have focus confirmation.
#1 is for my Super Takumar. It has a flange to depress stop down pins.
#2 goes on my S-M-C Takumar. This one doesn't have an inner flange because that would collide with the S-M-C open aperture metering hardware. This adapter still allows for stopping down via the Auto / Manual switch on the lens.
#3 is made specially for Fujinon EBC and Mamiya-Sekor SX lenses. EBC and SX lenses have open aperture metering architecture which makes it difficult to use them with conventional adapters. It will also work fine with "normal" M42 lenses.
All my adapters were bought from ebay. And I'm familiar with Japanese M42s, but don't know much about European or Russian lenses.