[ducdao]

I read somewhere that the Auto Takumar 55/f1.8 and Auto Takumar 55/2 are in fact the exact same lens. It's also said that Pentax basically took the 55/f1.8 then put a ring somewhere inside to prevent the the lens to be fully open at f1.8 then mark it as 55/f2.

If the above is true, has anyone identified the ring and somehow manage to make the 55/f2 to act like the 55/f1.8? I have a few 55/2 laying on my table right now and would like to try it for fun

[Just1MoreDave]

This post would cover it for a Super-Takumar:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/124763-super-t...ml#post1290780

The Auto-Takumar is built a little differently, so that advice might not apply. You'll notice the different construction right from the start. If you remove the "Name" trim ring, there aren't any screws under it. The front barrel just unscrews.

[pacerr]

If you look through the front lens of the Auto-Tak 55/2.0 in the right light you can clearly see a fixed aperture ring in front of the aperture blades and there is a final click stop beyond f 2.0. But you might also note the non-circular aperture formed by the individual blades at f2 - 2.8. I would suspect you could remove the false aperture ring but the exposed aperture circle may not produce bokeh to your liking - especially to gain so little from f2.0 to a nominal f1.8.

Given the current prices. I doubt you'd increase the value or saleability of the lens by modifying it.
H2

[ducdao]

If you look through the front lens of the Auto-Tak 55/2.0 in the right light you can clearly see a fixed aperture ring in front of the aperture blades and there is a final click stop beyond f 2.0. But you might also note the non-circular aperture formed by the individual blades at f2 - 2.8. I would suspect you could remove the false aperture ring but the exposed aperture circle may not produce bokeh to your liking - especially to gain so little from f2.0 to a nominal f1.8.

Given the current prices. I doubt you'd increase the value or saleability of the lens by modifying it.
H2

Thanks for the detailed instructions.

No, I'm not modifying it to increase the re-sale value nor the saleability of it. I have a couple Auto Takumar 55/f1.8 already. I'm making the mod just for the sake of trying something new. Just imagine a potential test of my modified 55/2 versus one from a friend for example. I already have the picture of his face when he sees the comparison results in my mind right now

[ducdao]

This post would cover it for a Super-Takumar:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/124763-super-t...ml#post1290780

The Auto-Takumar is built a little differently, so that advice might not apply. You'll notice the different construction right from the start. If you remove the "Name" trim ring, there aren't any screws under it. The front barrel just unscrews.

Thanks, Dave. That gives me a very good direction on what to do with my Auto Tak.

[cahudson42]

Some years ago I heard somewhere that the 55MM F2.0s were optics that flunked the test for being an F1.8. Supposedly, the F1,8 yield was terrible at the time, so rather than throw the flunked ones out, they got packaged as F2,0s for the SP500.

Anyone ever hear about this, or know if its true or not?

[jeffshaddix]

Any luck with this conversion? Anyone know if the 2.2 auto tak is the same way?

[octy]

Any luck with this conversion? Anyone know if the 2.2 auto tak is the same way?

Bumping this ancient thread for 2.2.