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04-02-2009, 07:27 AM   #1
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Join Date: Apr 2009
Location: Tavistock, Devon.
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Pentax f1.2 Disassembly

Hi All,

I'm new to this forum, having found it whilst trawling the WWW.
I have an f1.2 SMC Pentax which has a serious infestation of the dreaded fungus.
I've successfully taken apart various other lenses (50mm f1.4, 55mm f1.8, etc.) with no problems, but the f1.2 doesn't seem to want to come apart in the same way as the others. Normally the ring with the writing on the front unscrews to give access to the front group but with the f1.2 the name ring only unscrews a couple of turns before it binds against the smaller diameter (52mm) filter thread.

I'm totally stumped on this one, and any thoughts would be much appreciated. I could, of course, send the lens to a repairer but it's been around the block a few times and I could end up spending money that would be better spent on another one, though I know they don't come cheap.

Any suggestions gratefully received!

Best wishes,


04-02-2009, 10:17 AM   #2
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No recommendations, unfortunately, but I am interested in hearing how you make out. Please consider taking some photos during the breakdown/reassembly and posting them here so we can all benefit from your experience.
04-02-2009, 04:12 PM   #3
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Join Date: Mar 2009
Location: Adelaide.
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are you working on the A verson or the K version....mechanically they are both quite different.

but on the K version the ring with the writing doesn't lead anywhere but the ring on the front of the focus barrel leads to the three focus adjustment screws. and by removing those you can remove the first couple of lens elements.
04-02-2009, 06:40 PM   #4
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Location: Brisbane, QLD, AUS
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Excellent. Mayhap I should fix my beloved $25 K f1.2.

04-03-2009, 01:32 AM   #5
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Join Date: Apr 2009
Location: Tavistock, Devon.
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Original Poster
Thanks for the comments so far.
Digitalis - I'm working on the K version. I see that the front quarter inch or thereabouts of the lens (in which the filter thread is) is stepped down to a fractionally smaller diameter than the lens barrel behind it, though even looking through a magnifying glass I couldn't decide whether the filter thread is a separate ring. If it is then to avoid it coming undone when removing a tight filter it must presumably either a) be done up very tightly or b) have an anti-clock thread (though I've never before come across one on a Pentax lens).
Best wishes,
04-30-2013, 03:07 AM   #6
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Join Date: Aug 2010
Location: SEQ
Posts: 293
I know this thread is old, but old lenses will be around for years to hopefully this post may help other owners of this magnificent lens who are up to trying their own maintenance.

My recently acquired fungus-filled K 1.2 was going to be thrown away(!) by the lady from whom I bought it if it wasn't sold..."It belonged to my ex - I just want it gone!", she told me. I told her that I was happy to take it, thank you very much!

Apologies for the quality of the pics...they are "quick and dirties".

Based on the OP's most recent post, it is clear he did not understand what Digitalis was trying to explain....and neither did I until I fluked upon it just by handling the lens. As previously stated, "the ring on the front of the focus barrel leads to the three focus adjustment screws".
I thought that ring was actually part of the focus barrel. It is not. See the the ring, partially unscrewed, below:

Once this ring is off, it's very straightforward. Focus to the minimum focusing distance, and this exposes the three screws that need to be removed next. One of the screws is visible in the pic below:

Once the housing, which includes the filter thread (and stops the faceplate from being removed any sooner) is removed...

...then the faceplate can be unscrewed...being careful, as this is the only thing holding the front element in place.

The next group can then be unscrewed and removed (and also separated for cleaning) and this then exposes the aperture blades, and the inside of the rear group.

This is as far as I needed to go...and therefore wasn't willing to go further unnecessarily.

Once cleaning is completed, do everything in reverse to put back together.
Not bad for a total investment of 20 bucks!
04-30-2013, 03:53 AM   #7
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Join Date: Apr 2009
Location: Netherlands
Posts: 346
Don't ask where I found this on the net, I do not remember anymore, but its a not very good copy of the exploded diagram of the K 1:1.2/50mm

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