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04-25-2012, 10:10 AM   #1
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Strangest lens problem ever.... Pentax-M* 300/4

In the no so distant past, I picked-up a Pentax-M* 300/4 lens from a fellow forum member which aside, from a few nicks and scratches, seemed to perform admirably.

Having said that, after putting the lens away for a few weeks, I decided to mount the lens on my gimbal head for a little eagle watching when I noticed that the I couldn't get the lens in focus. Which was confusing as the focus ring would hit its limit long before the lens would reach infinity.

And so I unmounted the lens, and after careful examination found that the entire glass assembly inside the lens seems to be advanced by about 1" from the flange. That is to say that when I turn the focus ring to its theoretical limit, that the elements inside will travel so far inside the lens casing that it will exceed the travel tube limits and expose the inner parts of the lens! - make sense?

Anyways, I just wanted to throw this out there and ask if anyone had every seen anything like this? TBH. I have no idea whatsoever how this could have happened as the lens has no signs of having fallen or being hit etc. And more importantly... how one could fix such a thing?

04-25-2012, 10:36 AM   #2
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The lens might have been opened up before and the internal groups might have moved or loosened internally. Your lens would need to be collimated for infinity focus. Best to send to a lens repair tech who can do this.
04-25-2012, 10:57 AM   #3
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yep, I agree....most likely somebody was 'fixing' the lens.....shame, because it is perfect glass....and pitty, cause it is expensive piece...
never had such problem with mine....
04-25-2012, 10:59 AM   #4
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QuoteOriginally posted by creampuff Quote
The lens might have been opened up before and the internal groups might have moved or loosened internally. Your lens would need to be collimated for infinity focus. Best to send to a lens repair tech who can do this.
Hi Creampuff!
First off, I'd like to thank-you for the quick response.
The thing of it is, I can't for the likes of me figure-out how this could happen. Everything with the lens seems to be tight and working as intended.
However, the rear element group is out of alignment by a very large margin I'd say.

I guess I don't have much choice at this point given that I don't have the means to repair it. Kind of sucks though that this would happen just before the puffins got here

Having said that, based on your own oppinion, do you think it is conceivable for someone to adjust the lens focus themselves?

04-25-2012, 11:15 AM   #5
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Okay I just discovered something that I think might help solve this mystery.
I was fiddling with the lens trying to look for evidence that it might have been dropped or something while I wasn't around and I noticed that if/when I turned the focus ring quickly, that I can feel the mechanism(inside) slipping. That is to say that the ring seems to slip without moving the focus elements, which incidentally I was able to coax the lens back where it should be. However... the problem obviously isn't solved as the lens will inevitably go out of alignment just as soon as the focus ring is turned hard enough for it to slip. And so the question now becomes whether or not someone like myself could fix this at home? ie. are there screws that can be adjusted for this type of thing?
04-25-2012, 12:21 PM   #6
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I'd suggest sending it to Eric (Home) for a free estimate on repair.
04-25-2012, 12:28 PM   #7
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Completely different lens but recently I dropped a 55-300 DA-L. The focus ring was jammed and the thing would not focus at all. Not to worry I thought, a good excuse to lash out on a f2.8 sports zoom. However with some manipulation back to front of the focus ring while rotating, it all slipped back into place and the thing is now as good as ever. It seemd like it had just jumped a cog
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