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Converting M series lens to manual
Posted By: GUB, 12-02-2014, 10:00 PM

There is an established trick of not clicking your M lens all the way home on its mount to achieve total manual control of the lens.
The camera can then be used in AV mode. I now drill a custom locater pin hole at the right point to achieve this.
I learnt this trick of creating a custom lens lock pin hole from people on this forum a while back. But I have not come across a thread showing how to do it. So apologies if there is one out there.
The chances are if you have some M lens then you have a sick SLR body to cannibalize.
Mark approximate top dead centre (A) on the lens mount of the SLR.
Mark which hole is the lock pin hole(B).
Take (unscrew the 3 little philips screws) the lens mount off the body.
Turn the mount over and remark those points on that side. (I used twink)
And also mark the screw hole (C)
Put your lens on the mount like you were putting on the camera and get top dead centre to the top.
Now when you drop a small punch (screwdriver) thru the pin lock hole (B) it should drop in and locate the lens in its pin lock groove.
Centre punch through the screw hole (C). This is where you need to drill the custom hole.
I use a 2.5mm drill in a drill press and drill just far enough that the full diameter hole is forming.
I then take another 2.5mm drill that I have ground the bevel tip off (see image) to mill the hole so it has a flat bottom.
The aim is to end up with a flat bottomed hole that is around 1mm deep.
This hole is just over 9mm from the old pin lock locater groove.
If you so wish you can create this hole 1 - 2 mm closer but you run the risk of the lens not totally stopping down.
Please note that my camera goes tramping with me , bounces around in my farm truck and getting generally abused but I sense no stability issues with the lens being only part way on.

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12-03-2014, 07:10 PM   #16
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QuoteOriginally posted by vonBaloney Quote
I think there was an old and newer version of the Porst, but I could be mistaken. I have the Revuenon 55 1.2 (Cosina-made) -- might be the same lens. Maybe I could see a photo of yours?
Here is photo of both Porst lenses 55f1.2 I owned, one with the aperture linkage removed, the other one (right) still has the aperture arm intact. I can use the one the left in Av mode, but I can only use M mode with green button for the one I did not change.

https://picasaweb.google.com/lh/photo/tAliltQPasdjeCyyT2Si3tMTjNZETYmyPJy0li...eat=directlink


If I need to sell the lens, I can put the aperture linkage back into the lens.

12-04-2014, 03:27 PM   #17
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QuoteOriginally posted by aleonx3 Quote
Here is photo of both Porst lenses 55f1.2 I owned, one with the aperture linkage removed, the other one (right) still has the aperture arm intact. I can use the one the left in Av mode, but I can only use M mode with green button for the one I did not change.

https://picasaweb.google.com/lh/photo/tAliltQPasdjeCyyT2Si3tMTjNZETYmyPJy0li...eat=directlink


If I need to sell the lens, I can put the aperture linkage back into the lens.
When I reassembled my Sears/Cosina lens, I did it wrong and the prong on the aperture ring was in the wrong place to catch correctly and work the iris so it worked like taking the ring out. This way you don't have a chance of loosing the part in case you would like to sell it. I would imagine the same situation would occur with other brands of lenses.
12-04-2014, 03:41 PM   #18
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QuoteOriginally posted by Rimfiredude Quote
When I reassembled my Sears/Cosina lens, I did it wrong and the prong on the aperture ring was in the wrong place to catch correctly and work the iris so it worked like taking the ring out. This way you don't have a chance of loosing the part in case you would like to sell it. I would imagine the same situation would occur with other brands of lenses.
If it works out just fine, then it's all that matters. I keep the linkage part and screws all in a small plastic zip-log bag with sticker label in a safe place along with the lenses.
10-29-2015, 02:29 PM   #19
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So if I have this right, the lack of K-mount aperture linkage is the reason why Taks are not a problem?

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