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12-12-2010, 03:07 AM   #1
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Modifying a Pentax lens

Recently I bought a Canon 60D to use as a video camera in difficult environments where a normal video camera wouldn't be practical. I would have liked to have kept to Pentax but the lack of manual video controls on the Pentax offerings killed any chance of that for me.

I am still keeping my K10D and my Pentax lenses though. But I am interested in perhaps modifying some of my old lenses to work on the 60D.

For example I have a SMC Pentax-M 1:1.7 50mm prime that I would like to use. This lens doesn't have an A or M selector like my older M42 mount lenses. But I was wondering if there was a way of taking off the lever that prevents manual iris control when it is mounted to the camera body? And also whether it is possible to modify it so that there are no hard iris stops?

Lastly would any of this be possible without permanently destroying the lens? In other words can it be done so that it can be returned to its original state if required?

12-12-2010, 03:19 AM   #2
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For Canon APS-C DSLRs, just a PK-EOS adaptor will do. It can be had very cheaply on eBay, or the MIJ one being 12000+yen. The difference is mostly in craftsmanship and thickness preciseness.

mount adapter
12-12-2010, 03:46 AM   #3
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Will I be able to control the aperture manually though as it doesn't have an A-M selector? Could be a bit tricky if I have to use f1.7 all the time.
12-12-2010, 06:34 AM   #4
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QuoteQuote:
...For example I have a SMC Pentax-M 1:1.7 50mm prime that I would like to use. This lens doesn't have an A or M selector like my older M42 mount lenses. But I was wondering if there was a way of taking off the lever that prevents manual iris control when it is mounted to the camera body? And also whether it is possible to modify it so that there are no hard iris stops?...
Yes to all.

It is easiest to cut the lever, but it can be removed or might be otherwise disabled.

There's a little ball under the aperture ring which can be removed to make it click-less.

DIY or hire someone. These are not difficult modifications.

Dave

12-12-2010, 07:00 AM   #5
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I'm pretty good with diy technical stuff. Though all the guides I have found so far say to cut the lever off. Do you know of any guides that show how to disable the lever without having to do this?
12-12-2010, 07:10 AM   #6
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QuoteOriginally posted by SimonMW Quote
I'm pretty good with diy technical stuff. Though all the guides I have found so far say to cut the lever off. Do you know of any guides that show how to disable the lever without having to do this?
As I recall, the Canon makes no use of the lever & it doesn't interfere with the camera if you just jam the lever in the desired position (remove the spring, wire it back, whatever.) Look at the camera's mount to be sure.

Dave

PS to explore removing the lever, remove the lens' rear mount plate & look at the lever mechanism; there may simply be a screw holding the lever in place.

Last edited by newarts; 12-12-2010 at 07:16 AM.
12-12-2010, 03:52 PM   #7
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QuoteOriginally posted by SimonMW Quote
For example I have a SMC Pentax-M 1:1.7 50mm prime that I would like to use. This lens doesn't have an A or M selector like my older M42 mount lenses. But I was wondering if there was a way of taking off the lever that prevents manual iris control when it is mounted to the camera body? And also whether it is possible to modify it so that there are no hard iris stops?

Lastly would any of this be possible without permanently destroying the lens? In other words can it be done so that it can be returned to its original state if required?
Eliminating the hard iris stops is easy. It usually happens all by itself, when it's not the desired effect. This photo shows what the lens looks like with the mount removed:



Then you can slide off the aperture ring and it'll look like this:



The stops are caused by a spring-loaded ball bearing on the left, near the orange diamond. Just remove that and no more hard clicks.

I don't have a Canon but I think the aperture lever doesn't interfere unless it's a full-frame camera. But don't take my word for it.

There are three screws that were hidden by the aperture ring, into the side of the lens. Removing those allows you to remove the aperture control mechanism. It's sometimes tight but should come off. Here it is:



At the top of that photo is the lever. It's riveted on, with a little fork on it that connects to the aperture blades. You need the fork part, otherwise the aperture ring won't move the blades. I'm not sure if the fork is separate from the lever. Drilling out the rivets might work but the rivets are difficult to replace. Maybe bending the lever would work, and that's reversable. The mechanism is interdependent; I don't see a good way to eliminate the lever without affecting the aperture ring.

There's a light shield in the mount that can be removed if you have a really small screwdriver.
12-13-2010, 01:43 AM   #8
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There is no need to remove the rear lever with Canon APS-C bodies.

12-13-2010, 06:16 AM   #9
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QuoteOriginally posted by wlachan Quote
There is no need to remove the rear lever with Canon APS-C bodies.
Thanks!
12-13-2010, 07:05 AM   #10
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Excellent guys, thanks. I have ordered two adaptors off eBay, one for my K mount lenses and one for my M42 ones.
12-13-2010, 05:26 PM   #11
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If you use M42 lenses, look for the pre-set type. These will allow you to change your aperture between fully open and a preset f/stop.... silently and steplessly.
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