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02-22-2016, 03:50 PM   #1
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Super Takumar 55/1.8 infinity focus adjustment

Hello!

I recently acquired a Super Takumar 55/1.8. It's very well preserved, smooth focus, no oil on the blades. Although I can't get it to focus to infinity. I'm using it on a Sony A5100 with a M42 adapter. I know when it comes to such problems adapters are usually to blame, but I have a set of other M42 lenses that all focus to infinity without a problem and with no prior adjustments.

First I thought it was just that my focusing ring was not properly adjusted, so I followed this guide: Shooting with a Pentax K10D: Fixing the infinite focus on a Super Takumar 24mm ... . I had no luck adjusting the focusing ring. Even if I removed the focusing ring and rotated the focus as farthest to infinity as I was able to get it, it still didn't achieve infinity focus. I unscrewed the helicodial and played with different setups of the two helicodial parts, no luck with that either, it would just stop before reaching infinity. I then unscrewed the 3 little screws that are holding the optics block attached to the helicodial and removed the optics. I could then see that the part that held the optics couldn't go any further back into the lens because it hit the aperture lever mechanism. I read this guide aswell: https://www.pentaxforums.com/forums/114-maintenance-repair-articles/217082-ta...egreasing.html trying to find some answers why this was happening. I still have no clue, I'm beginning to think that the lenses themselves might not be properly set up, but I don't want to rush into dissasembling the optics itself. Another thing I tried was taking out the middle helicodial part and just sliding in the optics on the two rails as far back as it would go until it hit the aperture mechanism, same result as before, almost at infinity but not quite. I believe the lens also comes flush with the adapter since I filed down the aperture pin so it comes flush with the lens body. Is there something else I could attempt to do? Thank you.

02-22-2016, 04:53 PM   #2
PRS
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Hard to say without an image but it sounds like the 3 screws you removed are the ones that allow the focus ring to move the lens barrel. Put one back and tighten, then see if you can adjust focus by moving the focus ring. If you can, then loosen, move the focus ring and tighten until test you get infinity focus in the right place. When done, replace the other 2 and reassemble front of lens.
02-22-2016, 11:51 PM   #3
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QuoteOriginally posted by PRS Quote
Hard to say without an image but it sounds like the 3 screws you removed are the ones that allow the focus ring to move the lens barrel. Put one back and tighten, then see if you can adjust focus by moving the focus ring. If you can, then loosen, move the focus ring and tighten until test you get infinity focus in the right place. When done, replace the other 2 and reassemble front of lens.
Thank you for the reply. I can actually turn the focus barrel by gripping the part where the 3 screws come in, the brass part. The problem is that even if I rotate it like that towards infinity it will jam before reaching infinity. And I don't think it jams because of the helioids, but because it hits the aperture mechanism and cant go further back. I'll post some pictures later to clarify.
02-23-2016, 12:18 PM   #4
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Posting some pictures for clarity.


The lens with the focusing grip/ring removed. I was turning the brass part by hand, there is a two directional arrow next to it.


Brass part rotated to about halfway towards minimum focus distance (the whole optics block moves further out). 1 is the brass part that I rotated, 2 is the helicoidal that holds the optics block and 3 is the optics block.


Optics block removed from the helicoidal, so I was able to better see what was going on.


Close up inside the helicoidal. As you can see the helicoidal hits the aperature mechanism causing it to stop. The lens is not at infinite focus when this happens, this is the reason that I'm so confused, since I don't see how adjusting the helicoidals differently would allow the lens to move even further back thus achieving infinite focus.

I would be very glad if somebody has a solution to this. Thank you.

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02-24-2016, 08:44 PM   #5
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QuoteOriginally posted by okacat Quote
The lens is not at infinite focus when this happens, this is the reason that I'm so confused
That is understandable. The lens helicoid is at the near limit of its travel and you don't have infinity focus. Having ruled out the adapter as the next question is whether the optics are complete and properly assembled. I have not done this repair, but perhaps one of our members with experience with servicing this lens will drop in on this thread.


Steve
02-25-2016, 11:06 AM   #6
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Thank you for such a comprehensive post. Sadly there is no cutout on to the helical, it has the same range of back movement no matter in which of the two possible orientations I insert it. I've tested this with the brass part removed, that way I could slide the helicoid down on the rails and rule out that the brass part is limiting movement. Even if the helicoid had a cutout the optics block would hit the aperture lever less than a millimeter later.

About the aperture lever, I've observed some pictures from the other thread: https://www.pentaxforums.com/forums/114-maintenance-repair-articles/217082-ta...egreasing.html


Namely this one.

The aperture level's assembly looks the same on my copy, although the whole can't be observed completely from the picture above. I've inspected the lever and it doesn't seem that there would be any way to assemble it differently, it looks and functions correctly as it is now.

Right now the only idea that I have left is that the optics block itself is not properly assembled, like stevebrot suggested.

Again, thanks for all the help, I really appreciate it.
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