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12-21-2015, 09:00 PM   #1
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Focus ring offset or no infinity focus? (Mamiya 55mm F/1.4)

Hi all.

So I recently acquired via Ebay an Auto Mamiya / Sekor 55mm F/1.4 m42 lens. This (beautiful) lens appears to be in reasonable shape, except for one major thing: the focus ring doesn't reach infinity focus. This is as far as it goes:

However, in testing the lens, I can take shots of fairly distant objects at F/2 or F/2.8 and have them be in pretty good focus, as far as I can tell. For example, below is a scene where the most distant building is three blocks away, along with a 100% crop. It was shot at, I think, F/2.8. Would I be wrong in concluding that the lens probably does correctly focus at (or very near) infinity and the focus ring simply has an "offset"? Based on the photos below, that seems a lot more likely than the other possibility, which is that the lens really only focuses to about 4m. According to an online depth of field calculator, if the lens was really focused at 4m, even at F/4, the DoF would only reach to about 4.5m, so the building in the shot below would be way out of focus, no? Also, the focus ring does seem to travel quite a bit beyond the closest marked focus distance (0.5m), which again is consistent with the focus ring being offset. Thoughts? If you think I am correct, does anyone know if that might be a fairly easy thing to adjust/repair?

12-21-2015, 09:14 PM - 1 Like   #2
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I concur. The ring lies.
12-22-2015, 01:10 AM   #3
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Someone possibly has had a play with the focus ring calibration, likely due to use on another camera system. I have found this with some Pentax M lenses I have bought. For example, the infinity stop needs to be reset for use on Canon dslrs if infinity focus is to be achieved (addresses the slight difference in registration distances between the two systems.

As dcshooter suggests, there should be some screws that allow the ring to be disengaged from the focus mechanism, realigned and then retighted. On Pentax M, these screws lie behind the front name plate. I defer to dcshooter's knowledge of where these screws lie on a Mamiya lens. I would use live view on a distant target (with focus peaking if you have it) to work out when the infinity setting on the ring and true infinity focus (as seen in the live view) are correctly aligned. Using a tripod so you have your hands free to make the adjustments is the best way to perform this task. Should be a five minute job once you have located the correct screws.
12-22-2015, 06:49 PM   #4
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QuoteOriginally posted by dcshooter Quote
3 tiny set screws on the exterior of the focus ring, hidden in the grip knurls. Hit them with solvent first so you don't strip the heads.
I believe you can see the screws that dcshooter is referring to quite well in the pictures provided at the top of this PF thread. However, my copy (all black, serial #200498) doesn't have those screws! Not a single screw in the grip knurls. I guess there must be at least two versions of this lens... I'm now thinking that if it's just the focus ring lying, it's really not a very big deal. But I'll put that lens at the front of the queue when I want to start tinkering with lenses!

Thanks all!


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