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08-02-2010, 06:16 PM   #1
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Yet another hack job -- OM to PK ??

So I won an eBay auction for a Vivitar 25/2.8. Hey, I have an Albinar (Tokina) 25/3.5 with the aperture stuck open; I thought maybe the Viv would be a little better. And it only cost US$2.25 + $8 shipping. Whatta deal! So it arrived today... and it's 35/2.8. So I've sent a little note off to the seller demanding replacement or refund. (Seller says no returns, and it ain't worth returning anyway.)

But to the point: It's an OM mount. I check the ever-useful Camera Mounts Sorted by Register page and see that the PX register is 45.46mm and the OM register is 46mm. So it seems possible to pull the OM mount and replace it with a PK mount -- for totally manual operation, of course.

So, my question: Has anyone here ever chopped an OM lens and stuck it on their PK cam? Or do I have another sacrificial victim here?

08-02-2010, 06:20 PM   #2
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It's not a sacrificial victim, yet.

OM to PK is one of the easier conversions to make. You will need a file or dremel, however.

There're some details on this thread:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/23284-zuiko-ol...es-pentax.html
08-02-2010, 06:29 PM   #3
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I couldn't find the thread but long time ago I read either here or in one of the manual lens forums, that someone successfully did the conversion. It was a 28mm lens if I remember correctly. The OM mount register distance is slightly longer than Pentax, so if you just switch the mount with Pentax one which say has the exact same thickness, you won't lost infinity focus. Instead, the infinity mark on the lens will get you to focus to slightly beyond infinity.

I have two Nikon mount lenses. Nikon has 46.5mm register distance (0.5mm more than OM). I can mount the lenses to my *istDS without doing any convertion (not perfectly but firm enough), and I can focus to beyond infinity.

EDIT: hangu gave the thread link. I read it and it's quite more complicated than what I remember

Last edited by sajah; 08-02-2010 at 06:40 PM.
08-02-2010, 07:03 PM   #4
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You think that's complicated? Try FD/Exakta/Alpa. OM is definitely one of the easiest, slightly more work than Contax/Leica R.

08-02-2010, 07:14 PM   #5
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Om > pk

I converted a Tamron 300/5.6 in OM mount to PK a while back. I used a Tamron Adaptall PK adapter for the replacement mount. I essentially ended up with an M-type 300/5.6.

In that particular case I was intending to make a short-focus 300mm lens and accepted the nominal 3mm extension ring effect that resulted. That about halved the short focus range and limited max range to about 180 feet. Results were as good as the original lens.

Had I wanted to achieve infinity focus I'd have "shaved" the adapter on a lathe and reused the attaching screws. But since this was a field expedient exercise I simply epoxied the adapter to the lens. Now I sort'a wish I'd used a less permanent solution just so I could play some more with the combination.

H2
08-02-2010, 09:31 PM   #6
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QuoteOriginally posted by hangu Quote
Thanks for that link! And it points to a page on the MFLenses.Com site with another OM-PK conversion that uses a flanged M42-PK adapter, which I may try. Meanwhile, here's where I am so far:
_ _ _ _ _

This is a Vivitar lens with an OM mount, not a Zuiko lens; the mount details differ. I have three PM female mounts to test lenses on: my K20D, my ZX-M, and PK mounts from a set of macro tubes. The V-OM base fits snugly on the ZX-M's polycarbonate (plastic) mount, but not on the metal receptacles of the others.

The macro-tube mount is thin, with visible workings, so I can watch the action from inside. It looks like the leading edge of one of the V-OM bayonet flags doesn't quite clear the thickness of the metal receptacle flags. Tomorrow I'll drag out the Dremel and try thinning those leading edges a little, enough to grip.

The other option is to replace the lens base. Alas, I have no PK lenses I wish to kill -- I ain't broken any yet. I have some Nikon-mount TC's I can do without, but their bases aren't readily removable. And I have some flanged adapters. I can't measure this, but an adapter *looks* like it's no more than 1/2mm thicker than the V-OM base. So if flag-shaving doesn't work, I'll proceed to adapter-drilling.
08-03-2010, 12:25 AM   #7
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QuoteOriginally posted by RioRico Quote
Thanks for that link! And it points to a page on the MFLenses.Com site with another OM-PK conversion that uses a flanged M42-PK adapter, which I may try. Meanwhile, here's where I am so far:
_ _ _ _ _

This is a Vivitar lens with an OM mount, not a Zuiko lens; the mount details differ. I have three PM female mounts to test lenses on: my K20D, my ZX-M, and PK mounts from a set of macro tubes. The V-OM base fits snugly on the ZX-M's polycarbonate (plastic) mount, but not on the metal receptacles of the others.

The macro-tube mount is thin, with visible workings, so I can watch the action from inside. It looks like the leading edge of one of the V-OM bayonet flags doesn't quite clear the thickness of the metal receptacle flags. Tomorrow I'll drag out the Dremel and try thinning those leading edges a little, enough to grip.

The other option is to replace the lens base. Alas, I have no PK lenses I wish to kill -- I ain't broken any yet. I have some Nikon-mount TC's I can do without, but their bases aren't readily removable. And I have some flanged adapters. I can't measure this, but an adapter *looks* like it's no more than 1/2mm thicker than the V-OM base. So if flag-shaving doesn't work, I'll proceed to adapter-drilling.
Look around for a junk type TC (focal, etc) and use the mount from that.

08-03-2010, 12:32 PM   #8
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Pop over to Leitax website, they've just developed an OM to PK mount kit for reversible mount conversions.
Olympus OM lens for Pentax cameras

08-05-2010, 09:46 PM   #9
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QuoteOriginally posted by xjjohnno Quote
Pop over to Leitax website, they've just developed an OM to PK mount kit for reversible mount conversions.
Olympus OM lens for Pentax cameras
There is also an adapter for Leica to Pentax.

Someone on this forum told me I was wrong when I said you can fit a Leica and Olympus to Pentax so just in case they didn't see my post with the adapter links, here is the Leica to Pentax.

Leica & Pentax & Nikon | Leitax

I don't understand why people don't do a simple google search before they start accusing people of being wrong. It took me 2 minutes to find both of these adapters.
08-06-2010, 02:42 AM   #10
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We can fit a wide range of lenses on Pentax, check this link : Adaptation d'objectifs via des bagues [Topic Unique] - Page : 10 - Objectif - Photo numérique - FORUM HardWare.fr (third post, and an other one later in the topic)
08-07-2010, 02:24 PM   #11
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QuoteOriginally posted by xjjohnno:
Pop over to Leitax website, they've just developed an OM to PK mount kit for reversible mount conversions.
Thanks. I'm unlikely to buy a 65+ Eu adapter for a US$2 lens, however.

QuoteOriginally posted by KxBlaze:
Someone on this forum told me I was wrong when I said you can fit a Leica and Olympus to Pentax...
That was possibly myself. But I may have said (or meant) that there's no simple way to mount Leica LTM, Canon FD, Oly Pen, and other short-register lenses on Pentax cams, while retaining infinity focus. I don't count as simple either optical adapters, which change FL and speed, nor surgical adaptations that require chopping the lens body to attain infinity focus.

QuoteOriginally posted by CarbonR:
We can fit a wide range of lenses on Pentax, check this link...
Merci! For those of us who have no French (including myself), here is an English translation.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Meanwhile, where I am now: I tried replacing the V-OM mount with a flanged M42-PK adapter. On this lens, it doesn't work. The Vivitar OM mount has a ~5mm rim that holds the aperture ring in place; the adapter lacks such a rim. So I must grind away a bit of the V-OM bayonet flags. That will happen in a couple days. Stay tuned.
10-06-2010, 07:11 PM   #12
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Any update on the V-OM to PK adaption?

I took off my vivitar 55mm 1:1 mount only to find out it was designed differently from regular OM mounts.

It's pretty ridiculous on how it controls the aperture. You can't simply tie them together or else it will be at f16 when the ring is set to f5.6.

Ugh.. well there's the body mount mod but then M42 lenses are loose?

Last edited by Eruditass; 10-06-2010 at 07:26 PM.
10-06-2010, 08:16 PM   #13
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QuoteOriginally posted by Eruditass Quote
Any update on the V-OM to PK adaption?
Ah, I guess I should have updated this. The mod of the Vivitar 35/2.8 went very smoothly. I used a Dremel cutting blade that had already been worn down from cutting other metal parts. I used its edge and side to taper the tops of the leading edges of the lens' bayonet blades.
Definitions: By 'top' I mean the surface that's AWAY from the camera; and by "leading edge" I mean the part that first engages with the blades on a PK mount. By 'taper' I mean I changed that leading edge from blunt to wedge-shaped.
The blades on this lens are about 1mm thick. With the cutting tool, I reduced the thickness at each leading edge to about 0.5mm, and tapered it back about 8mm. I have no OM body (yet) to test this on, but it looks as though it should still fit firmly onto an OM body. But I also removed the mount-grip gear and the aperture flags (in the way on a PK mount) so if this ever sees an OM again it'll be totally manual and unsecured.

I don't know what to say about your Viv 55. I don't even have any other OM lenses (yet) to refer to. I didn't have any prescribed procedures to follow here, I just made it up as I went along. Good luck.
10-06-2010, 09:08 PM   #14
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QuoteOriginally posted by RioRico Quote
Thanks. I'm unlikely to buy a 65+ Eu adapter for a US$2 lens, however.

. . .
The Oly 24/2, 28/2, 35/2, 100/2 etc. are a different matter. Those are what the Leitax were developed for.
10-06-2010, 09:39 PM   #15
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QuoteOriginally posted by Blue Quote
The Oly 24/2, 28/2, 35/2, 100/2 etc. are a different matter. Those are what the Leitax were developed for.
How good are they exactly?
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