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10-09-2012, 07:29 PM   #1
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Advice on using a screw mount lens with a pin on a K5

hi All,

I have two lenses that I would like to try out on my K5. However, I am not too familiar with screw mount lenses, so any advice on if these might work would be most helpful.

The first lens is a 35mm W. Carsen F3.5.

The second lens is an 85mm to 205mm macro Opticam II F3.8.

My guess is that they are M42 screw mount lenses, so I am thinking that picking up a Pentax Mount Adapter K will do the trick.

However, the part that I am uncertain of is on the 85mm to 205mm lens, there is a pin sticking out of the back of the lens which when pressed closes the aperture. I am concerned this might not allow the lens to be mounted using the adapter. Has anyone seen this before, or knows if the lens will fit properly?

I've attached 4 photos showing the lenses for clarity. The first two are of the 35mm lens, and the last two are of the 85mm to 205mm lens. In the third photo, you can see the pin I referred to earlier.

Thanks!

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10-09-2012, 07:34 PM   #2
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If there's no manual diaphragm clutch, then you're right, you won't be able to stop this down.

Here are the instructions you'd otherwise need to follow to use m42 lenses:
https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html

Adam
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10-09-2012, 07:47 PM   #3
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The pin is normal -- it is on most m42 lenses and doesn't affect mounting. The Carsten will work fine as-is (with an adapter). However, on the zoom, as Adam pointed out, if there is no "auto-manual" switch (to set to manual) you won't be able to stop down the lens because nothing will be pressing on the pin. (But maybe it has one?) However you can glue it down and then it will stay pressed all the time.
10-09-2012, 07:55 PM   #4
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Thank you for the replies. There is no switch to set the aperture into manual mode.

Cheers,
-Eric

10-09-2012, 08:31 PM   #5
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QuoteOriginally posted by montreal.eric Quote
Thank you for the replies. There is no switch to set the aperture into manual mode.

Cheers,
-Eric
Yeah, some lenses you might not want to glue the pin down for fear you couldn't undo it (although theoretically you can with acetone) and find a mechanical solution by disassembly, but I just glue them (I also assume I'm keeping it forever). That lens, however, has a resale value of approximately zero dollars, so I wouldn't worry about -- good one to practice on.

As far as adapters, you'll need a "non-flanged" model or else you won't be able to focus to infinity...
10-09-2012, 09:37 PM   #6
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QuoteOriginally posted by vonBaloney Quote
Yeah, some lenses you might not want to glue the pin down for fear you couldn't undo it (although theoretically you can with acetone) and find a mechanical solution by disassembly, but I just glue them (I also assume I'm keeping it forever). That lens, however, has a resale value of approximately zero dollars, so I wouldn't worry about -- good one to practice on.
I glued my Yashinon DS 50mm f1.9, but if it was a f1.4 or even an f1.7 I might have thought twice. I don't think there are any die hard auto aperture M42 body users that are just dying to get a 50mm f1.9, not that I ever plan on getting rid of it.
10-09-2012, 10:39 PM   #7
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QuoteOriginally posted by elliott Quote
I glued my Yashinon DS 50mm f1.9, but if it was a f1.4 or even an f1.7 I might have thought twice. I don't think there are any die hard auto aperture M42 body users that are just dying to get a 50mm f1.9, not that I ever plan on getting rid of it.
I've glued down the pins on my Yashinon DSM 50/1.4, Yashinon DSM 50/1.7, Helios 58/2, a couple Meyer/Pentacon 50/1.8s, some Mamiya/Sekors, and a few others I've forgotten. I've sold a few with them glued down -- I think it is an improvement because there are very few people looking for them to use on m42 auto-aperture film cameras, and lots looking to use them on digital and might be afraid to do the modification themselves. Acetone *should* dissolve it, but I've never actually tried it.
10-09-2012, 10:52 PM   #8
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Gluing a lens is not quite as bad as the people chopping the aperture stop down tab from a Pentax K 50mm f1.2 so it can be used on a full frame Canon. I'll probably end up gluing others too, but for something that might have value I'll try a more elegant modification first, like the common one for some Helios lenses that uses a little plastic tube. I didn't even bother trying to get that Yashinon apart, I just glued it, .

10-09-2012, 10:52 PM   #9
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It looks like it would be very easy to take the back off the lens, assuming you've got an appropriate screwdriver. If you do this, you should find that you can achieve what you want by using a short piece of plastic tubing to hold the pin in a depressed position.

Not only is this easily reversible, but I think it's generally a more satisfactory solution (at least for those lenses whose backs can be easily removed, which it appears this is).
10-10-2012, 01:15 AM   #10
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You need to modify a bit to use the zoom lens, but it is reversible as resell value.

Unscrew the mount then use a small plastic tube to insert into the pin and prevent it to go back.
The lens is now in fully manual mode.

As for the plastic tube, I cut from electrical wire. Find one with correct size, cut it in correct length, then insert.
You may need to unscrew one or two inside the mount, where pin mechanism locates.
Use good screw drivers, mine are of JIS type (japanese industrial standard). Japanese lenses do not use Philip head.

Edit: m42man was here before me
10-10-2012, 03:34 AM   #11
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There are two ways to do this, the first is an M42 mount with a flange to depress the pin, the second is a mod as proposed by hoanpham or as shown in this thread
https://www.pentaxforums.com/forums/pentax-beginners-corner-q/131036-how-stop...m42-mount.html
10-10-2012, 04:04 AM   #12
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This is great! Thanks everyone for your advice. I think I will go for the disassembly/depression of the pin.

Cheers,
-Eric
10-10-2012, 10:03 AM   #13
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QuoteOriginally posted by montreal.eric Quote
This is great! Thanks everyone for your advice. I think I will go for the disassembly/depression of the pin.

Cheers,
-Eric
This is usually easy, remove the screws holding the mount to the lens. Then take the end of a ball point pen refil (about 3mm or 1/8 inch ) and slip it between the mount and the base of the pin
10-10-2012, 06:07 PM   #14
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Sounds good. Thanks again!

Cheers,
-Eric
10-10-2012, 09:32 PM   #15
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Thanks for everyone's help. Attached are pictures of the process and final result, works as expected!

As a note, when I first tried the 3mm size ball point pen refill piece, I was unable to set the aperture of the lens to F3.8 (wide open). The aperture ring wouldn't turn to it. I had to make the size of the pen refill piece smaller (maybe 1.5mm) to allow for the full aperture range.

I found out that it helps to check the aperture range before screwing everything back together

Cheers,
-Eric
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