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05-26-2019, 01:44 PM   #1
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Sudden 35mm f/3.5 focus alignment problem

Hi everybody. I've got a brainteaser of a problem for you all.

I've got a 645z that I've been using for the past few years with a 55/2.8 and a 35/3.5. My bread and butter.

A couple of weeks ago I picked up the 35mm and accidentally pushed the rear element in a bit when my thumb slipped while the lens was in AF mode. I attached the lens to the body and autofocused (via the rear AF button), but the focus was completely off. The camera 'found' focus and stopped like it was correct, but it was very much not correct. This was true of close and far distances.

I flipped the choke to manual focus, and racked the focus back and forth a bit and when I click it back into autofocus while at infinity got it to work correctly. At least temporarily. It's been doing the same thing intermittently since. The best way I can put it is that it feels like the lens is "out of alignment' with where it thinks it is. By doing the MF to AF trick I can get it back on track most of the time. Like setting a broken bone or something. I've never had a previous problem with the lens. When it's focused correctly, the image looks great. As far as I can tell, the sound of the lens focusing hasn't changed. There are no crunching sounds or broken gear sounds that I can hear.

Anyone else ever had a problem like this and know what to do to fix it? I've done some searching on the forum to no avail, but it's one of those issues that's hard to describe.

Thanks so much.

Bill Wadman

05-26-2019, 04:45 PM   #2
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I can't offer any help at the moment; I'm afraid of what might happen if I tried to duplicate your experience. I will observe that I am astounded that a lens element can even move with thumb pressure (relative to its barrel). Normally, lenses are located (fixed) by metal retainers and spacers. The glass would have to fracture to move.

Am I missing some aspect of your description?
05-26-2019, 04:54 PM   #3
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QuoteOriginally posted by kaseki Quote
I can't offer any help at the moment; I'm afraid of what might happen if I tried to duplicate your experience. I will observe that I am astounded that a lens element can even move with thumb pressure (relative to its barrel). Normally, lenses are located (fixed) by metal retainers and spacers. The glass would have to fracture to move.

Am I missing some aspect of your description?
Nope, as I recall I barely put little pressure on it, like I said my thumb slipped and pushed it. I was surprised as well.
05-27-2019, 09:19 AM   #4
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I just looked at mine. It appears that the rear element is supported by some soft material. Also, the overall design appears to be fairly complex and going at it with optical ring spanners might be an experiment in how to permanently disassemble the optics group and supporting mechanical parts. I can only suggest finding a shop that repairs or even just cleans the interior lenses of Pentax lens assemblies. They would know how to take it apart. Perhaps that is all that is needed to reset the support into its proper position. Cost may equal buying another used 35mm on eBay, however.

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35mm, 35mm f/3.5 focus, 645, 645d, 645z, af, alignment, autofocus, bit, camera, choke, f/3.5 focus alignment, focus, lens, medium format
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