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10-16-2011, 01:16 AM   #1
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50mm/f4 Macro Focus Problem

I got hold of a 50mm Macro M42 lens from the usual online auction site. It is a bit tatty but clean and works nicely at short range. However, I have a suspicion that somebody has been inside it before. The back-end of the lens is not properly secured to the front - it moves very slightly although all the screws I can see are tight. However, the main problem is that the lens doesn't quite make it to infinity focus. It seems to be mechanically stopping too early as the infinity symbol doesn't get to the mark and it seems able to go further before it hits the mechanical stop.

Having read through a number of posts here I had a go at opening the lens. However, when I get the data ring unscrewed from the front there is nothing useful under it-no screws or rings. Looking at the other end of the lens there is no obvious way to disassemble it from there either. Has anyone taken one of these apart, or have a copy of the mythical Lens Repair Manual to give me some help on where to start? Many thanks.

10-16-2011, 01:40 AM   #2
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Just to throw in this fact I've run across on a different lens. The helicoid has three or four tracks, so it sounds as someone had taken it apart completely and re-seated it a turn out of position. The other thing is that usually the guides that keep the lens barrel straight in the other barrel are possibly set wrong in the tracks and so the wobble. You can observe them from the rear when the lens is turned to the closest focus. I've not had the luck in acquiring the M42 or the K version of the macro, so I hope these clues are not too far off.
10-17-2011, 10:26 AM   #3
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What's the exact model? I don't remember having any trouble with the Pentax-M 50mm f4 Macro, but that's a 1:2 macro. Some of the M42 versions do 1:1 and therefore have more complex focusing.
10-17-2011, 02:01 PM   #4
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It's the M42 1:2 version. There is nothing obvious under the data ring at the front, and the rear element has no cut-outs to allow unscrewing. Moving the lens to close focus only appears to reveal the slot for the aperture control

10-17-2011, 06:53 PM   #5
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OK, I was half wrong about the M version. The trim ring comes off like most M lenses, and you can access a lot of internals there, but no focus adjustment. It's under the rubber grip. If your Takumar has screws on the focus ring, probably three common ones, they are what you need. Loosen them and see if the ring turns without actually focusing the lens. Then turn the ring a bit away from infinity, then tighten and see if that was enough.
10-18-2011, 02:41 AM   #6
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QuoteOriginally posted by Just1MoreDave Quote
OK, I was half wrong about the M version. The trim ring comes off like most M lenses, and you can access a lot of internals there, but no focus adjustment. It's under the rubber grip. If your Takumar has screws on the focus ring, probably three common ones, they are what you need. Loosen them and see if the ring turns without actually focusing the lens. Then turn the ring a bit away from infinity, then tighten and see if that was enough.
I've tried that. You will remember from the lens that the whole lens apparatus moves. Regardless of how I adjust the focus ring with the 3 grub-screws you describe, the lens still hits a mechanical stop at just before infinity. It is that adjustment, if indeed it is adjustable, that I need to get at.

By the way, I am not using the lens on a DSLR with an adaptor ring so that's not the problem. I have it on my Spotamtic F.
10-18-2011, 10:13 AM   #7
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They had to put it together somehow. The only thing I can suggest is the way an Auto-Takumar 55/1.8 comes apart: the front barrel/filter ring unscrews, trim ring and all.

The amount that even the 1:2 macros extend make construction a little unusual, so there could be something unique to this lens, which no one seems to have taken apart before. Maybe take photos of the lens, as much detail as possible, and post them here.
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