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03-31-2009, 09:53 PM   #1
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Old lens compatibility

I have recently acquired a K20d with the 18-50 lens and now exploring the use of some older lenses. I found a M50 1.7 and have been enjoying the lens. I have a couple of old school lenses from my 35mm days and was wondering if I would have any issues using them on the K20 body.

Both are M42 thread, so I purchased the Pentax adapter. However both have a pin that protrudes from the back of the lens for aperture activation. I want to be assured that this configuration will not physically conflict with the camera body when the lens is used.

Rexatar Auto 135mm 2.8
Meyer Optik Oreston 50mm 1.8

I have read most of the posts concerning the use of older lenses and have not found a direct solution. Some information seems to indicate that the pin(s) need to be removed and or defeated. Other information seems to indicate one an mount the lens with no issues.

Any insights are appreciated

Lane

03-31-2009, 10:11 PM   #2
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Hi,
Good to see that yet another Pentax user is exploring the universe of vintage glass!

You don't need to worry about any of the lenses that you note above. They should be compatible without modification.

Here are the only serious concerns regarding older glass:
  • The genuine Pentax M42 (screw mount) K-mount adapter is your friend. Other adapters are available, but some do not allow for infinity focus and others may be very difficult to remove from your camera.
  • Certain K-mount lenses may have the dreaded "Ricoh Pin". These lenses include all Rikenon P and many 3rd-party models made for the Ricoh program camera bodies. They have "P" on the aperture ring. This pin will jam into the auto-focus drive coupler on the body and make the lens almost impossible to remove.
  • Certain M42 lenses lack the auto/manual switch or slider that allows the diaphragm to operate in full manual mode. These include screw mount versions of the Russian Zenitar lenses.

With the older lenses there is some loss of functionality:
  • Pentax-A series (have A position on the aperture ring) allow full meter and exposure functionality
  • Pentax-M and Pentax-K series support center-weighted and spot stop-down (green button) metering in manual mode
  • M42 screw mount support stop-down metering in AV and manual mode. Lens must be switched to fully manual aperture. Your Rexatar should have the switch on the side of the lens barrel. Your Meyer may have a switch, but may also have a preset rather than an auto diaphragm (two aperture rings).

With stop-down metering there is some variability in meter accuracy depending on aperture and lens.

Steve
04-01-2009, 03:35 AM   #3
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I have taken something like 15,000+ images with Takumar (M42) lenses coupled with the K100D and the K20D. You needn't worry about the aperture activation pin at all. Come on in and join the M42 fun!
04-01-2009, 05:45 PM   #4
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QuoteOriginally posted by stevebrot Quote
Certain M42 lenses lack the auto/manual switch or slider that allows the diaphragm to operate in full manual mode. These include screw mount versions of the Russian Zenitar lenses.
Yes. If you have a screwmount lens that has the aperture pin but NO auto/manual switch, then the lens won't stop down when mounted. Some people have done things like jamming the pin in with a broken-off piece of toothpick, gluing it in place, etc. Do these at your own risk!

But if you have an aperture pin AND an auto/manual switch, no modification is necessary.

And if you have NO aperture pin and NO auto/manual switch, no modification is necessary.

04-02-2009, 07:31 PM   #5
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Original Poster
To all,

Thank you for taking a moment to respond to my question. As I journey down the path of digital photography I will have to learn the nuances of the format while clinging to the lessons learned in the realm of 35mm. The vast knowledge available from the participants on this site will no doubt shorten my learning curve and will minimize the number of inevitable errors I will make.

I have tried both lenses and am looking forward to transferring my skill set from film to digital.

Lane
04-03-2009, 07:46 AM   #6
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QuoteOriginally posted by Quicksand Quote
Yes. If you have a screwmount lens that has the aperture pin but NO auto/manual switch, then the lens won't stop down when mounted. Some people have done things like jamming the pin in with a broken-off piece of toothpick, gluing it in place, etc. Do these at your own risk!
Actually (I think) the lens WILL stop down, but only in M mode - Green button use is highly recommended. Before I learned this, I superglued a few pins down. Now I'd like to un-glue them. Research indicated that acetone (nail polish remover) would do the trick, but alas! I'm now stuck (pun intended) with a few preset-only lenses.

As for the dreaded Ricoh pin - I have a couple Sears lenses made by Ricoh, lacking said pin. Whew. But if I ever encounter and purchase a Rikenon M42, will superglue do the trick, or is a hanksaw necessary?
04-03-2009, 11:03 AM   #7
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Is there a third party brand list somewhere of m42 lenses that are compatible with the k20d? I see some of these lenses from time to time online, but am weary of purchasing them.
Thanks for your help! Susan
04-03-2009, 11:13 AM   #8
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QuoteOriginally posted by Susan Quote
Is there a third party brand list somewhere of m42 lenses that are compatible with the k20d? I see some of these lenses from time to time online, but am weary of purchasing them.
Thanks for your help! Susan
Welcome Susan.
Here are two places to start, on this very forum; Pentax Lens Review Database - Main Index
and;
PentaxForums.com Third-Party Pentax Lens Review Database - Main Index

04-03-2009, 11:20 AM   #9
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QuoteOriginally posted by RioRico Quote
Actually (I think) the lens WILL stop down, but only in M mode - Green button use is highly recommended. Before I learned this, I superglued a few pins down. Now I'd like to un-glue them. Research indicated that acetone (nail polish remover) would do the trick, but alas! I'm now stuck (pun intended) with a few preset-only lenses.

As for the dreaded Ricoh pin - I have a couple Sears lenses made by Ricoh, lacking said pin. Whew. But if I ever encounter and purchase a Rikenon M42, will superglue do the trick, or is a hanksaw necessary?
M42 lens that has the aperture pin but no A-M switch will NOT stop down by the green button. There is nothing in the Pentax DSLR to push the lens's aperture pin in to close down the aperture.

The "dreaded Ricoh pin" exists only on some Rikenon bayonet mount lenses - the lenses that can be used in program mode. M42 Rikenon lenses do not have this pin.

QuoteOriginally posted by Susan Quote
Is there a third party brand list somewhere of m42 lenses that are compatible with the k20d?
If there is such a list, I have not seen it.

All M42 lenses can be used with the K20D. The only time you need to do the simple modification is as outlined above - when it has the aperture pin but no A-M switch.

M42 lenses can be stopped down manually, so Av mode works great. Set the camera body to Av mode, open up the lens to focus if needed, close the aperture down, hit the shutter release button. I actually prefer pre-set lenses.

Lenses with PK-mount can be modified so you can manually stop down the aperture. But this require drilling a hole on the mount of the lens, something many folks don't want to do.

Last edited by SOldBear; 04-03-2009 at 11:59 AM.
04-03-2009, 11:22 AM   #10
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QuoteOriginally posted by Susan Quote
Is there a third party brand list somewhere of m42 lenses that are compatible with the k20d? I see some of these lenses from time to time online, but am weary of purchasing them.
Thanks for your help! Susan
nearly every single m42 lens will work on your k20 with a proper m42-k adapter. because they all use the M42 × 1 mm standard. this is a metric screw thread of 42 mm diameter and 1 mm thread pitch. some m42 lenses (like some of the older CJ flektagon lenses) are actually to big to mount because they interfere with the flash housing. however this is just a size issue not a mount issue. if it is an m42 lens, it will work.

QuoteQuote:
M42 lens that has the aperture pin but no A-M switch will NOT stop down by the green button. There is nothing in the Pentax DSLR to push the lens's aperture pin in to close down the aperture.
the camera cant stop down the lens regardless of an auto/manual switch or aperture pin. on your K20 you will have to use the lens in manual so not having that switch is irrelevant.
04-03-2009, 11:58 AM   #11
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I do have the m42-k adapter. I have a couple of Takumars that I love using.
Thank you so much for taking time to answer my questins! Susan
04-03-2009, 02:11 PM   #12
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QuoteOriginally posted by séamuis Quote
the camera cant stop down the lens regardless of an auto/manual switch or aperture pin. on your K20 you will have to use the lens in manual so not having that switch is irrelevant.
Seamuis, the switch isn't irrelevant; SOldBear is right. Some "auto" or "automatic" M42 lenses without the auto/manual switch have no manual mode and won't stop down on their own. They were meant to use with cameras that have a mechanism to depress the pin to stop the lens down. I have a couple of Yashica lenses that work that way. That's why having the auto/manual switch (or something to jam the pin down on auto-only lenses) is needed to use the lens with a modern camera & adapter ring.
04-03-2009, 05:33 PM   #13
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QuoteOriginally posted by indytax Quote
Seamuis, the switch isn't irrelevant; SOldBear is right. Some "auto" or "automatic" M42 lenses without the auto/manual switch have no manual mode and won't stop down on their own. They were meant to use with cameras that have a mechanism to depress the pin to stop the lens down. I have a couple of Yashica lenses that work that way. That's why having the auto/manual switch (or something to jam the pin down on auto-only lenses) is needed to use the lens with a modern camera & adapter ring.
you learn something new everyday. thanks for sharing that with me.
04-03-2009, 09:33 PM   #14
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QuoteOriginally posted by RioRico Quote

As for the dreaded Ricoh pin - I have a couple Sears lenses made by Ricoh, lacking said pin. Whew. But if I ever encounter and purchase a Rikenon M42, will superglue do the trick, or is a hanksaw necessary?
Nah, I've converted a couple and it's not that bad. Usually, you just remove 4 screws holding the mounting flange, pull off the flange, remove the pin, then replace said flange. No tools needed other than a screwdriver.
04-03-2009, 09:53 PM   #15
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QuoteOriginally posted by Susan Quote
I do have the m42-k adapter. I have a couple of Takumars that I love using.
Thank you so much for taking time to answer my questins! Susan
Regarding a master list of M42 lenses...that would be nice, but oh, so hard to compile! Literally thousands of lens models were made in the M42 screw mount from the late 1940's up through the present time. (Yes, there are current production M42 lenses including various offerings from Russia and Zeiss ZS models.)

I guess the sheer variety of what is out there is part of the fun. I have several M42 lenses, some of them excellent, and all of them with a special characteristic that sets them apart.

Steve

(My avatar photo was taken with the LZOS MC Jupiter-9 85/2...M42 bought new from Russia last Spring...)
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