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Legacy Lenses Discuss the use of older lenses, using adapters, from the Olympus OM system, Leica M and R-series, and the millions of others too.

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Old 13th July 2012
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Help! OM 90mm macro

I have in my possession a OM Zuiko Auto-Macro 90mm f2. If i decide to keep it i will be using it with an OM-D. I am not at all familiar with this lens.

Anyway, i think there may be an issue with the iris. At f2 the iris is correct and fully open, however, when stopping down the iris is fine down to f4, and then closes a fraction to f5.6, at f5.6 the iris doesn't move any further. There are two metal 'long' buttons on the mount, when one of these buttons is pressed as the ring is rotated the blades seem to stop down correctly, and when this button is released the iris jumps back to the f5.6 position. The other metal button on the mount doesn't seem to do anything.

So is there a problem with the iris (as i suspect) or am i just not clued up enough, and unaware of a function/technique that is required to make this thing work? I am not at all familiar with these two metal buttons.

Looking forward to any replies.
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Old 13th July 2012
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Re: Help! OM 90mm macro

Oh, and i don't possess an adapter at this point.


edit: Ok, now my brain is slowly engaging i recall those buttons release the lens, i was confused as to why one of them effects the iris.

Would i be right in assuming the iris won't stop down properly unless it's attached to the camera?
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Old 13th July 2012
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Re: Help! OM 90mm macro

It's the way OM lenses work to enable full-aperture metering and focussing on OM bodies.

One of the two buttons on the mount is the lens release catch. This is the one with ridges on it that sits at 10 o'clock if you're holdng the camera in front of you in the shooting position.

The other one, without the ridges and at about 4 o'clock viewed from behind the camera, is the depth-of-field preview button. Normal operation on an OM body is that the lens stays open while you compose and focus, even though you can adjust the aperture to set the exposure. Then you can preview dof by pressing this button - although I always found it of limited use as the screen goes dark. So in theory if you keep this button pressed while you adjust the aperture ring you should see the diaphragm close all the way to f/22. If it doesn't, it may be that there is a problem with the diaphragm, or it may just be that the lilnkage with the preview butoon is not working properly.

To test it further, take the rear lens cap off and you should see two lugs poking backwards out of the mount. Looking at the lens from behind with the focus mark at the top, there is one which moves between about 1 and 3 o'clock as you move the aperture ring. This one communicates with the camera - it tells the camera how many stops down the lens is from full aperture so that the camera can do the exposure metering calculation without actually stopping down the lens. The other one normally sits at 9 o'clock but is spring-loaded and can mode round to about 10 o'clock. When you take the shot the camera body pushes this to the 10 o'click position which closes the diaphragm to your selected aperture. So to really check it you need to push that lever all the way clockwise to where it stops at about 10 o'clock and then adjust the aperture ring - you should see it stop down all the way.

When you put an OM lens on a 4/3rd body, the mechanincal linkage with the second lever isn't there - 4/3rds 9big and micro) do the stopping down electronically. The adapter should push it round to the stopped-down position which means the aperture willl close down as you twiddle the ring - so you don't get full aperture metering. best to compose with the aperture ring set wide open, then stop down to take the shot.

That's a bit waffly but I hope it explains what's going on. The OM 90/2 is a lovely lens so I hope you can get it working.

Ciao ... John
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Old 14th July 2012
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Re: Help! OM 90mm macro

Thanks a lot for that John. I used to have an OM10 way back, and that info is triggering vague memories, i suppose a lot of water has flowed beneath the bridge since then. But yes, it seems the lens may be ok after all, looks like i'll be receiving the adapter tomorrow (Sat) and i can't wait.
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Old 15th July 2012
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Re: Help! OM 90mm macro

Thanks again John for that post. Everything seems to be working fine. Now looking at extension tubes.
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Old 15th July 2012
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Re: Help! OM 90mm macro

Glad it's working Pete. Have you got the adapter now? You should be able to get pretty close without needing tubes - if memory serves it went to half life-size on 35mm full frame. So on 4/3 it will still be half-size but will fill all the frame rather than half of it, IYSWIM.

Ciao ... John
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Old 16th July 2012
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Re: Help! OM 90mm macro

Yes John i do get that, cheers for that. The reproduction ratio would be the same on M4/3 as it would be on FF, but as the M4/3 image needs enlarging more for printing purposes the size of anything on that image will effectively double.

It will be interesting to see what this lens can do on M4/3, right now there is just a lot of shake when handholding but i'm up for the challenge of taming that in time. I'll be keeping the lens which is in brilliant condition, seems like it's something of a collector's item.

This is a very small garden spider (hardly larger than a money spider) back lit by the sun, shot at f11 and RR 1:2 which is the maximum macro for this lens, and handheld and uncropped SOOC, i think it shows potential. Out of 60ish shots i'd say 7 were worth keeping (tbh a better ratio today than those i shot yesterday). Also, and typically for this type of lens, the bokeh is lovely.


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Old 16th July 2012
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Re: Help! OM 90mm macro

Lovely shot, Pete. Looks as if it would enlarge well, although it doesn't really need it as the composition with the web is great. The lens was highly regarded in OM days and commanded a secondhand price to match! It is quite chunky thanks to the close focus mechanism - as a contrast see if you can find a pic of the OM 85mm f/2, which is a little beauty.

Ciao ... John
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