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03-21-2008, 08:22 AM   #1
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Zuiko (Olympus OM) lenses on a Pentax?

I thought I remembered that someone on this forum had altered the mount of his Pentax DSLR (don't remember the type) to accept Olympus OM lenses... If true, could that someone please raise his hands and explain how he did that? A search on the forum didn't show anything usefull...

I have currently a Zuiko 85 f/2 lens which I would like to adapt to use on my ist D; anyone know if this is possible?

03-22-2008, 11:02 PM   #2
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Well, that would be me. But I altered my body mount to accept Contax lenses first, and it happened that the OM fitted as well. So I would like to know if the OM can be fitted on the K-mount without any further modification (that would be good for you).

If you look at the side of the OM bayonet, there is a very small screw, which is used to lock the lens in place in an OM body mount. You need to remove that screw. If you still can't mount the lens, you need to remove the auto aperture arm (i need to do this with my Zuiko 21 but not my Tokina 90). Like with all adapted lens, you wouldn't be able to use the auto exposure feature anyway, so this is not a big deal. If you still can't moun it, then we will talk about the mod.

By the way, the Zuiko 85/2 is a nice lens. The Zuiko f/2 series really has some outstanding contenders. I wished i have my paw on that Zuiko 21/2 but it's just too damn expensive now (I reget to sell it years ago).
03-24-2008, 07:37 AM   #3
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Txs Aegishpan!

Guess I have to try that. I have already seen that the only problem on mounting the lens on the camera is in fact the little screw. Will have a look at it...

Q: what exactly did you do to make C/Y lenses mount on the K10?
03-24-2008, 08:02 AM   #4
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I sand off 3 small pieces of metal in the back of the body mount, and cut off the M42 retention piece. Thus, the mod is irreversible. That's why I want to see if you really need the mod or not.

03-24-2008, 10:44 AM   #5
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Marc,
I have successfully converted my Cosina 28-70 F2.8 to K-mount. It is only manual at this time, but it works perfectly and focuses at infininty as well. The registration distance of the Olympus is 46mm, compared to 45.5 of the Pentax. This gives you 0.5mm for an adapter. Since my lens is less valuable, I reworked the lens. I used a M42 to K-mount adapter for the new mount and the adapter flange is just the right thickness to acheive the correct registration distance. Here is a link to my post with photos of the mount. I haven't finished the light baffle yet and intend to add a diaphraim coupling arm. Another issue with Olympus is that the diaphraim is spring loaded to the open position. It must be held in the closed position, so that you can adjust it with the appeture ring.

Dave

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/22469-mounting...-pentax-k.html
03-24-2008, 11:25 AM   #6
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Now were getting somewhere...

Txs Dave.

I'm first gonna try to get the Oly directly with modding here and there. If that doesn't work, I guess I could always try to dissassemble one of my K lenses to use the mount and convert it on the Zuiko...

Txs again, very helpfull!
03-24-2008, 02:36 PM   #7
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Marc,
I did a little research and found that the 85mm mount looks the same as my 50 F1.8. Lens manufactures tend to use the same mount design on most of their lenses. This is true of pentax as well. So you could do my simple mod on a mount from a cheap 50mm kit lens. This way the lens could be returned to its original state if so desired. I trimmed away the bayonet portion of the mount and dress down the mount face. I then used the OM mout as a pattern to drill the holes in the M42 adapter. Then I counter sunk the holes in the adapter to accomadate three flathead mounting screws. The adapter flange added the 0.5mm need to correct the focus at infinity.

Dave

Last edited by Big Dave; 04-26-2008 at 12:48 PM.
03-25-2008, 12:40 PM   #8
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Dave, English not being my first language (nor my second) and this being somewhat 'scary' to do for me (I'm not the best DIY'er at home ) , could you please go a little slower with me?

If I get this right, then (in chronological order) I should
  • buy me a Pilips screw driver?
  • unscrew the Oly mount (I see three little screws - I guess that are the ones?
  • buy me a driller (ok, I have one, but not sure if I have a drill with this tiny thickness)
  • use the Oly mount as counterpart to know where the wholes should be drilled in the Pentax mount (I have a 50 f/1,7 which is already taken apart, so finding one should be no problem)
  • Counterdrill to get the screw go in completely.

Now, talking of a little challenge... Pfew, sweat is already braking out, and I'm not yet started.

Questions:
  • Is my checklist ok?
  • How do I know how to place the two mounts on each other? I use the red dot as allignment?
  • The OM mount is designed to stay open. How can I adjust that?

Txs for the help all this way already... I'm considering in doing this very seriously, but then I can use all help I can. Txs again...

03-25-2008, 02:06 PM   #9
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I am eagerly following this thread for the Contax lenses. I am so thankful for your last question, as I am not that mechanically inclined either. Hope we'll get some answers with VERY simple instructions.
03-25-2008, 02:45 PM   #10
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Mount conversion does not work with every lens. However, if you have only 1 or 2 lenses that you want to adapt then mount conversion is probably a better choice (since it's easily reversible).

The problem with OM lens is that the auto diaphragm is always engaged. You need to come up with a solution to hold the auto diaphragm into preview position in order to effectively change the aperture.

I'll post right here the process to modify the body mount (it's more convenient than mount conversion, IMO). The following pictures are taken straight from a HK mod site:



Sand off the blue mark parts.



Before and after of the cut off M42 retention piece.

Those are the only necessary mod to mount a Contax lens. It might seem to be difficult, but it's less frustrating than some of my mount conversions.

With this mod, I can mount the OM lens directly on the K10D after the aperture mod.
03-25-2008, 03:19 PM   #11
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Hi aegisphan, the camera mod sound much easier for me.

Thank you for those illustrations. It looks like the two pieces shown in FIG#1 and #2 can be removed from the camera by unscrewing the 5 screws in the camera lens mount, right?

Can a metal file be used to sand the areas in FIG#1, and what can be used to cut the metal extensions in FIG#2.

Also, why is there a green circle in fig#2...what does that show?...the cut out areas are the protrusions, right? and has nothing to do with the part marked with the green circle.

Also, what do we lose by doing this mod? Is it only the inability to use M42 to K-mount adapter thereby being unable to use any M42 mount lenses?

What do you mean by losing auto exposure? The camera will meter with the green button right? or do we have to stop down to meter and then change the desired aperture after metering ? or do we have to carry around a light meter?

Thank you.
03-25-2008, 03:40 PM   #12
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In figure 1, you just need to unscrew the body, and the mod is done in the back of the mount. I use a small regular metal fill set to sand off those 3 spots.

After you remove the front mount, you will see this:



That's the same ring in Figure 2. However, there is a small electrical wire solder into this second ring in Figure 2 (right at the small protrusion at the bottom of the ring).

The purpose of this wire is to communicate EXIF info between the lens and the body. By loosing this contact, you wouldn't be able to change the aperture on the camera.

I used a very sharp/high quality wire snipper to cut off the L-shaped M42 retention piece (the green circle marks this piece). If you accidentally remove the ring from the wire, you can always solder it back, it's also a very easy process.

As for the exposure, all the adapted lens would act like a regular M42. You will have to do stop down meter (thus non-auto exposure): green button in M mode. The mod will still allow to mount a M42 lens, but the lens would move around when you focus or change aperture. So beside this minor setback, your pentax would function normally.

Edit: By the way, I PM you about the review of the new Zeiss line by Lloyd Chambers. In case you miss that, the review is very thorough. I would probably get the Zeiss ZK 35/2 soon, since it actually outperforms both the Canon 35/1.4 and Nikon 35/1.4. The 28/2 is not as well-corrected as the 35/2 (distortion and corner performance).
03-25-2008, 04:27 PM   #13
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QuoteOriginally posted by aegisphan Quote
In figure 1, you just need to unscrew the body, and the mod is done in the back of the mount. I use a small regular metal fill set to sand off those 3 spots.

After you remove the front mount, you will see this:



That's the same ring in Figure 2. However, there is a small electrical wire solder into this second ring in Figure 2 (right at the small protrusion at the bottom of the ring).

The purpose of this wire is to communicate EXIF info between the lens and the body. By loosing this contact, you wouldn't be able to change the aperture on the camera.

I used a very sharp/high quality wire snipper to cut off the L-shaped M42 retention piece (the green circle marks this piece). If you accidentally remove the ring from the wire, you can always solder it back, it's also a very easy process.

As for the exposure, all the adapted lens would act like a regular M42. You will have to do stop down meter (thus non-auto exposure): green button in M mode. The mod will still allow to mount a M42 lens, but the lens would move around when you focus or change aperture. So beside this minor setback, your pentax would function normally.

Edit: By the way, I PM you about the review of the new Zeiss line by Lloyd Chambers. In case you miss that, the review is very thorough. I would probably get the Zeiss ZK 35/2 soon, since it actually outperforms both the Canon 35/1.4 and Nikon 35/1.4. The 28/2 is not as well-corrected as the 35/2 (distortion and corner performance).
Thank you so much.

I'll have to trouble you more regarding FIG#2.

In FIG#2 the the part that is circled in green is still there in the after shot? it looks like it's just bent away in the 'after' picture, what is missing in the after picture are the extensions with the hole that snaps into the plastic protrusions in the camera.


Do we cut all those extensions with the holes that snap into the plastic protrusions in the camer body like shown in fig#2. It doesn't make sense to cut those off as the ring has to be mounted back, yet they are missing in the 'after' shot ?

Is the circled part bent away like in the 'after' picture. or should it be totally removed to be flush with the ring.

I have a soldering gun, so the wire is no problem. I was into RC heli's for a few months. Also, I don't have any M42 lenses and not planning to buy any, so no problems there either. I shoot in manual mode any way and use the green button all the time. So, it's a wonderful mod for me.

Thank you for the heads-up on the CZ 35/2 vs 28/2 it's highly helpful. I wonder how the CZ35/2 compares to Penatx 31mm limited.

Also, the reason for me to look into this mod is the availability of CZ 85mm in contax mount. But the lenses are slightly different with different filter sizes too.

The Carl Zeiss 85mm f1.4 Planar T* for K mount
https://photo-shop.zeiss.com/en/Products/1486-390

The Carl Zeiss 85mm f1.4 Planar T (missing the *) contax mount
Contax Carl Zeiss Planar 85mm f/1.4 SLR Lens(RESELLER RATINGS 1.96/10)

About a $400US difference in price...wonder whether they are comparable, what do you think?

Last edited by pcarfan; 03-25-2008 at 04:57 PM.
03-25-2008, 04:57 PM   #14
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The retention piece has the L shape, protrude radially in and then go downward. That's why you can't clearly see the change in Fig.2. By the way, the one of the left side is before the mod; it's an unconventional way to do before and after shot .

The extensions shouldn't be cut. In Fig2, the author would probably show a ring from his old Pentax camera. That's probably why he used the green circle to focus our attention to the M42 retention only .

The old Contax Zeiss does have T* coating like the new one. The optical design is the same as well. However, the new Zeiss does have a little modern tweak that, I would assume, yields a little better optical performance. However, the review is quite mixed on whether or not the improvement is there. If you look at 16-9.net review of the new Planar ZF 85/1.4, it performs not as well as it should, though the author said his copy might be a "duh" one.

From the Lloyd Chambers's review, he said that the new Zeiss ZF 85/1.4 and the 50/1.4 have "focus shift" issue. That is, when you change the aperture, the focus plane actually slightly moves forward. By f/2.8, the shift is minimized. So if you want to shoot at f/2, you need to manually stop down to f/2, focus, meter and shoot. The old Contax doesn't have this issue.

Thus, due to the high performance of the 77mm. i would suggest you to get that one instead (the same price as the old Contax, and 1/2 cheaper than the new Zeiss). However if you do want the Contax Zeiss, remember to get the MM version (it has slightly better optical performance than the AE version).

The 35/2, OTOH, is really interesting. Like you said, when stop down, it might actually outperform the 31LTD. The contrast and tonal are also outstanding. Bokeh is very nice, comparable to the Canon.
03-25-2008, 05:22 PM   #15
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QuoteOriginally posted by aegisphan Quote
The retention piece has the L shape, protrude radially in and then go downward. That's why you can't clearly see the change in Fig.2. By the way, the one of the left side is before the mod; it's an unconventional way to do before and after shot .
I am almost there now, the only question is, do you cut the entire L shaped piece or just the part that goes downwards and leave the part extending radially. Also, do contax lenses focus to infinity with this mod ?


I am so glad you mentioned the difference between the MM and AE versions. How do you tell these apart? (I just read the MM version will have the smallest aperture in green, is this true?) I absolutely love the way the new CZ 85/1.4 render...if the Contax is close then I will seriously consider this. What's a fair price in ebay ?

I've heard of the focus shift with some CZ lenses, but the way I understood that is very different. I've heard that the focus plane is not entirely flat, so if you focus on a flat sheet of paper wide open, it will focus most parts of the paper but some blotches will be out of focus. I didn't know it was to do with actual change of the focus plane with the aperture change. Are you certain of this ?, as that is a REAL pain.

I was so close to pulling tthe trigger on the CZ 85mm/1.4 but just couldn't get myself to pay $1k+ for it. Till I looked at the CZ 85 1.4, my favorites looking at flickr were the 31mm by far with the 77mm followed closely by the 43mm. But to me the CZ 85mm 1.4 bests them. I think I have to have it, but the price of the contax mount is easier to swallow.

Last edited by pcarfan; 03-25-2008 at 05:37 PM.
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