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03-03-2011, 10:56 AM   #1
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how do you change an olympus om lens to a k-mount

well i have an old olympus 50mm f1.8 lens and wanted to change it to k mount does any one know how to acheive this transformation thanks

03-03-2011, 11:10 AM   #2
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RioRico has modified the mount to force fit on a K-mount. Most of RR's modifications involve maniacally wielding a Dremel. Leitax sells a replacement mount but not for the 50/1.8, 28/2.8, or 40/2.

Olympus OM lens for Pentax cameras
03-03-2011, 11:18 AM   #3
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I have not modified an OLY lens personally, although there is a kit availab;e

Olympus OM lens for Pentax cameras

I have modified Kiron lenses for both Nikon and Minolta to pentax using flanged M42 to K mount adaptors and by removing the old lens mount. In both cases I had to grind extebsions off the existing aperture ring.

Don't know how the OLY lenses would shape up but clearly it looks easier when you see the link.

there are optically corrected adaptors for Minolta, Nikon and Canon to PK which are really simple teleconverters, with slight magnification to gaurantee infinity focus considering the increased camera to lens spacing

they have magnifications of 1/25 to 1.5x and really degrade IQ when used wide open.
03-04-2011, 08:41 PM   #4
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I did this with a Sears ( Tokina ) mirror lens. Remove the lens mount and cut off and smooth the lugs, the Oly mount should be flat when you are done. Figure out how you want to mount the Oly lens to the Pentax, some people like it twisted a bit so as to see the f/stop. Super glue a chrome plated brass flanged M42 to K mount adapter ( from ebay ) to the modded Oly mount in the correct orientation. Drill the holes from the Oly mount side through the M42 adapter ( use the Oly mount as a guide ) and counter sink the holes. The screw heads should be flush and smooth or they will scratch the camera. Stuff a bit of black foam in the slot where the lens removal push button was. Use the screws that held the Oly mount and attach the new K mount (and old Oly mount) to the mirror lens. For your lens, you will need to do more. You will have to deal with the aperture. Rig up something to stop the aperture down, as if you are pressing the stop-down button. I suggest getting a Pentax M 50mm f/1.7 and selling the Oly.

03-04-2011, 11:43 PM   #5
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Moved to the lens forum- this isn't a troubleshooting question.

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03-05-2011, 08:29 AM - 1 Like   #6
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My mod is simple and non-destructive, in that the lens can still be used on an OM mount. And the 50/1.8 is the second OM lens I modded. So here goes:

The problem with both OM and C/Y lenses viz PK mounts is that the bayonet flags on the lens bases are too thick to slide under the lugs of the PK camera mount. The solution is to taper the undersides of the leading edges of the flags, so that they *do* fit. I use a Dremel cut-off wheel #426 to shave away some of the flags' undersides, extending back about 10mm.

On an OM lens, do this to all three flags. On a C/Y lens, the leading edge of one flag has a notch in it, so only the other two flags need tapering. The lens will now force-fit onto a PK mount. If that seems too flimsy, use the Dremel to cut a slot 1mm deep and wide and 5mm long into the lens base in a position where the PK lens-lock pin will engage. THEN is is secure. And as I said, the lens can still be used on its native mount. Have fun!

NOTE: Another way to mod lenses is to remove the original base and replace it with a cheap safe flanged M42-PK adapter. I tried this with my first OM mod, a Vivitar-Tokina 35/2.8 but found that 1) it requires precisely grinding away some of the adapter, and 2) it messes-up the aperture linkages. Tapering the bayonet flags is much less problematic.

Last edited by RioRico; 04-03-2011 at 07:55 AM.
03-08-2011, 12:41 AM   #7
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QuoteOriginally posted by RioRico Quote
My mod is simple and non-destructive, in that the lens can still be used on an OM mount. And the 50/1.8 is the second OM lens I modded. So here goes:

The problem with both OM and C/Y lenses viz PK mounts is that the bayonet flags on the lens bases are too thick to slide under the lugs of the PK camera mount. The solution is to taper the undersides of the leading edges of the flags, so that they *do* fit. I use a Dremel cut-off wheel #426 to shave away some of the flags' undersides, extending back about 10mm.

On an OM lens, do this to all three flags. On a C/Y lens, the leading edge of one flag has a notch in it, so only the other two flags need tapering. The lens will now force-fit onto a PK mount. If that seems too flimsy, use the Dremel to gut a slot 1mm deep and wide and 5mm long into the lens base in a position where the PK lens-lock pin will engage. THEN is is secure. And as I said, the lens can still be used on its native mount. Have fun!

NOTE: Another way to mod lenses is to remove the original base and replace it with a cheap safe flanged M42-PK adapter. I tried this with my first OM mod, a Vivitar-Tokina 35/2.8 but found that 1) it requires precisely grinding away some of the adapter, and 2) it messes-up the aperture linkages. Tapering the bayonet flags is much less problematic.

can you focus to infinity with this mod to the lens i mean the dremel mod
03-08-2011, 04:45 AM   #8
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QuoteOriginally posted by lguckert79 Quote
can you focus to infinity with this mod to the lens i mean the dremel mod
In a word: Yes.

07-06-2011, 07:57 AM   #9
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ZUIKO OLYMPUS OM on PENTAX K mount

QuoteOriginally posted by RioRico Quote
My mod is simple and non-destructive, in that the lens can still be used on an OM mount. And the 50/1.8 is the second OM lens I modded. So here goes:

The problem with both OM and C/Y lenses viz PK mounts is that the bayonet flags on the lens bases are too thick to slide under the lugs of the PK camera mount. The solution is to taper the undersides of the leading edges of the flags, so that they *do* fit. I use a Dremel cut-off wheel #426 to shave away some of the flags' undersides, extending back about 10mm.

On an OM lens, do this to all three flags. On a C/Y lens, the leading edge of one flag has a notch in it, so only the other two flags need tapering. The lens will now force-fit onto a PK mount. If that seems too flimsy, use the Dremel to cut a slot 1mm deep and wide and 5mm long into the lens base in a position where the PK lens-lock pin will engage. THEN is is secure. And as I said, the lens can still be used on its native mount. Have fun!

NOTE: Another way to mod lenses is to remove the original base and replace it with a cheap safe flanged M42-PK adapter. I tried this with my first OM mod, a Vivitar-Tokina 35/2.8 but found that 1) it requires precisely grinding away some of the adapter, and 2) it messes-up the aperture linkages. Tapering the bayonet flags is much less problematic.
Hi RioRico, I am about to take a dremmel and chop to modify the zuiko lenses to fit the pentax K mount as you describe, so that i have already took some pictures just by forcing and holding the lens on the camera and it works... i was wondering if you are so kind to show some close pictures of what you've done before i make a mistake myself.
07-06-2011, 03:59 PM   #10
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QuoteOriginally posted by nachezman Quote
Hi RioRico, I am about to take a dremmel and chop to modify the zuiko lenses to fit the pentax K mount as you describe, so that i have already took some pictures just by forcing and holding the lens on the camera and it works... i was wondering if you are so kind to show some close pictures of what you've done before i make a mistake myself.
Pictures, eh? Wait a little bit. Don't do anything rash! I am converting another 50/1.8 right now, and I will post before-and-after photos soon. Two notes:

1) I use a Dremel #426 Reinforced Cut-Off Wheel; a package of five cost me US$12 at a local hardware store. Ordinary discs for cutting plastic and thin wood will not cut nor shave metal well.

2) I *strongly* recommend that you have a cheap PK macro tube set. Fit the lens (the victim!) into the macro set's female mount section. This way you can clearly see how the lens bayonet blades block against the mount lugs.

Wait. I shall return soon.
07-06-2011, 06:37 PM   #11
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QuoteOriginally posted by RioRico Quote
Pictures, eh? Wait a little bit. Don't do anything rash! I am converting another 50/1.8 right now, and I will post before-and-after photos soon. Two notes:

1) I use a Dremel #426 Reinforced Cut-Off Wheel; a package of five cost me US$12 at a local hardware store. Ordinary discs for cutting plastic and thin wood will not cut nor shave metal well.

2) I *strongly* recommend that you have a cheap PK macro tube set. Fit the lens (the victim!) into the macro set's female mount section. This way you can clearly see how the lens bayonet blades block against the mount lugs.

Wait. I shall return soon.
Ok, I'm getting a cheap macro tube...and then i'll wait your return, many thanks!
07-06-2011, 06:55 PM - 2 Likes   #12
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OK, I'm back. Here you see the 'before' and 'after' of chopping the Zuiko 50/1.8.

'A' and 'B' mark the area to trim on each bayonet flag. 'C' is the aperture stop-down button. Your goal is to taper each flag from the full thickness (A) to the thinnest edge (B). The distance from A to B is about 10mm. You don't want to cut through the metal body, just taper that flag. This allows the lens to be force-fit pretty tightly onto the PK mount.

For security, you can cut a slot about 1mm wide and deep and 6mm long in the lens base, for the PK locking pin to fit into. I did not do this because my new cutting disc is too large, >30mm; it hasn't been worn down enough yet! I usually wait until it is about 10mm before I cut locking slots in the lenses I have chopped.

I put a strip of metal tape over the stop-down button (C). Something like this is necessary, else the aperture remains wide open. Other possibilities are to jam a thin piece of wire to hold the button down; or insert a screw against the aperture flag; or take off the lens base, remove the stop-down button, and replace the base. I did the latter with my first OM modification. But with metal tape (or even duct tape), the lens can still be used normally on an OM camera.

Ah, this afternoon was a heavy chopping session! Much too hot to work outside, so I put a wood plank over my bathroom sink as a working platform. Besides the Zuiko Auto-S 50/1.8, I also chopped a Zuiko Auto-T 135/3.5 (OM), Soligor C/D 135/2.8 (N/AI), and Yashica DSB 50/2.9 (C/Y). I used a rocket blower to remove metal dust from each lens after the chopping. And everything works! I didn't screw-up anything! !Que Milagro!

The final picture shows the 50/1.8 mounted on my K20D, shooting itself in the bathroom mirror. Now it's your turn. Good luck!

.
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07-07-2011, 09:52 AM   #13
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Si, un milagro! Many Thanks Riorico, with these instruction I'll dare to start myself, I'll wait for the macro mount and then buy the proper disks for the dremmel, I'll let you know if I don't destroy it all, but it seems to be not so hard. Use last quest: does the light metering works on M mode without any issue on a k-5? Gracias de nuevo.
07-07-2011, 10:23 AM   #14
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QuoteOriginally posted by nachezman Quote
Si, un milagro! Many Thanks Riorico, with these instruction I'll dare to start myself, I'll wait for the macro mount and then buy the proper disks for the dremmel, I'll let you know if I don't destroy it all, but it seems to be not so hard. Use last quest: does the light metering works on M mode without any issue on a k-5? Gracias de nuevo.
No, it is not difficult. Documenting the work took much longer than doing it! Just use a gentle touch, and be careful that metal dust doesn't fly into your eyes. HINT: It doesn't hurt to practice first. Take an old broken lens and trim the bayonet flags.

I have a K20D not a K5, but metering should not be a problem. I use my modified lenses in Av, M, and X modes, just like any other fully manual lens. These work the same as an M42 lens on an adapter: stop down, meter, shoot. !Buenaventura!
07-07-2011, 11:20 AM   #15
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Nice job, by the way, both the documentary and chopping... so far it is the one and only method to have lenses K+OM mount all together. Enhorabuena y gracias de nuevo.
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