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05-17-2011, 01:13 PM   #1
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lens not mounted at 12 oclock

so I am going to modify an olympus lens to use on my pentax. unless I'm missing something, it should be the easiest conversion in the world. remove the original flange, drill 3 holes in a 42m-k adapter, screw it on with a .75mm shim (give or take a little) and I'm done.
reading a thread on how someone else did it, they say the hole for the pentax lens lock is in the way so you can only use 2 mounting screws. they said you could rotate the location of the holes to use all 3, but then the lens would not be 12 oclock and they acted like that would be a big deal. why would that be a big deal for the lens not to be at 12 oclock.?

fyi I know the flange distance difference is .54mm but my m42-k adapter flange is a little thinner than the om flange. I can play with different thickness shims. also, when I remove the om mount on this lens, most of the guts (buttons and levers and such) come with it and stay attached to the flange so I don't think there will be any problems with clearance.

05-17-2011, 01:38 PM   #2
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I have a Jup-9 that doesn't mount at 12' and it annoys me... but doesn't really do anything else as near as I can tell... Ap controls and focus is just a little cock-eyed
05-17-2011, 01:52 PM   #3
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so thats the only problem, the controls are in a slightly different location?
05-17-2011, 02:02 PM   #4
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QuoteOriginally posted by ripit Quote
so I am going to modify an olympus lens to use on my pentax. unless I'm missing something, it should be the easiest conversion in the world. remove the original flange, drill 3 holes in a 42m-k adapter, screw it on with a .75mm shim (give or take a little) and I'm done.
There is an extra step, see here https://www.pentaxforums.com/forums/lens-clubs/34323-zuiko-lens-club.html

You need to add a piece of wire on the aperture lever to keep a functionnal aperture

05-17-2011, 02:17 PM   #5
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QuoteOriginally posted by Jieffe Quote
There is an extra step, see here https://www.pentaxforums.com/forums/lens-clubs/34323-zuiko-lens-club.html

You need to add a piece of wire on the aperture lever to keep a functionnal aperture
yea I had read about that but hadn't seen any pictures that I could tell where they are tying it. It didn't really matter as it was just a matter pining back the aperture lever. your link has a decent pic (easier than what I was thinking of doing) so thanks.
05-17-2011, 02:49 PM   #6
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Incidentally, there is a company that makes a replacement K-mount for OM lenses:

Olympus OM lens for Pentax cameras
05-17-2011, 06:50 PM   #7
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That's kind of expensive for the lenses I have but it sounds good if you have a really nice lens.

Anyway, I kind of got it and kind of trashed it (can be fixed). The flange on my adapter is .030" and the screw heads are .025 inch so obviously I couldn't just cut a countersink for the screw head. I use a roll pin punch (I was lucky enough to have one the same exact diameter as the screw head) and drove a detent for the screw head. It has the added bonus of increasing the thickness of the flange by nearly the perfect amount so it is self shimming. The bad news is, I drove the punch completely through the adapter. I used a screw pitch gauge (steel plate with different size threaded holes to check screw fit) as a back plate. it acted just like a punch and die and cleanly cut a hole the size of the screw head. I was a little more car full on the next 2 and they worked (one looked like I almost hit to hard but its good). So I have 2 working screw holes with a punched it countersink/shim. The adapter cam out a hint too thick (just a matter of a few thousandths of an inch), so I can actually gently file down the back of the punch mark to fine tune it to the exact distance. I tried it out and it works fine.

I'm thinking I could just redo the holes at a different spot. The old holes would just act as additional shim points. I'm also thinking of some sort of superficial shim to fill the gap for aesthetics and or fill the old holes with black epoxy to cover them cosmetically (and a modified body cap for the center though that was someone else's idea.
05-17-2011, 07:32 PM   #8
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I filed it down to nearly the right thickness for the pictures.


Last edited by ripit; 04-23-2013 at 10:41 PM.
05-17-2011, 07:37 PM   #9
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more pics. on the side shots look at where the 3 is and you can see where it shimmed itself up.

Last edited by ripit; 04-23-2013 at 10:41 PM.
05-17-2011, 08:05 PM   #10
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I'm not sure if the focus is dead on but it focuses down to 1 foot and at 50 feet, I'm almost but not yet at the end of my adjustment. It's too dark out to tell more.
05-17-2011, 09:00 PM   #11
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There's nothing to be gained by being anal about the twelve o'clock alignment and I feel it's inconvenient as well. I usually intentionally set 'em up that way (not at 12 o'clock) when tweakin' an M42-PK adapter.

I prefer that the older lenses with aperture rings mount with the aperture index mark at about the two o'clock position so it's not hidden by that $%#@* flash bulge and I can actually see what I've got set.

( "It's not a bug, it's a feature." -- to quote Microsoft. )

H2

Last edited by pacerr; 05-18-2011 at 06:27 PM.
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