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06-17-2010, 12:36 PM   #1
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M-42 adapters - a few questions

Hi all,

A few questions regarding M-42 lens adapters (for a K-7):

1. Are the ones on e-bay that say "allows infinity focus" just as good as Pentax ones? I see some listed for like $5-$10. I did find some info saying they may not be machined as well as the genuine one, but is that important if I want to do number 2 below?

2. Can they be mounted on the lens instead of the camera? (So when you remove the lens from the camera, the adapter stays on the lens.)

3. Do any exist that allow auto-apeture (shutter-priority)? I assume not.

Thanks!
Greg

06-17-2010, 12:42 PM   #2
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1. the ones that say they allow infinity focus are made to get 'at least' infinity focus, in other words there is a good chance they will go past too so you have to watch out. The Pentax OEM adapter on the other hand is flush with the mount, meaning the lens will sit up against the mount, as intended. You can find it on the pentaximaging website for mid-$30's and it is well worth it! Unless....

2. you want to glue one to all your m-42 lenses

3. you got it!
06-17-2010, 01:00 PM   #3
Ole
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Regarding no. 2:

If you use the genuine Pentax adapter you will have to remove its locking mechanism. Then you can mount it permanently on the lens. I'd assume that the non-Pentax adapters would have a locking mechanism as well which you'd have to remove.

The problem with that approach is that the lens-with-adapter combination won't lock in place on the camera like a genuine K-mount lens, so you have to be careful that it doesn't twist and fall off by itself.
06-18-2010, 07:08 AM   #4
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QuoteOriginally posted by GregX999 Quote
Hi all,

A few questions regarding M-42 lens adapters (for a K-7):

1. Are the ones on e-bay that say "allows infinity focus" just as good as Pentax ones? I see some listed for like $5-$10. I did find some info saying they may not be machined as well as the genuine one, but is that important if I want to do number 2 below?

2. Can they be mounted on the lens instead of the camera? (So when you remove the lens from the camera, the adapter stays on the lens.)

3. Do any exist that allow auto-apeture (shutter-priority)? I assume not.

Thanks!
Greg

Be careful. I have seen adapters on ebay that claimed infinity focus, but were, in fact the type with the wide flange that will NOT allow infinity focus. Study the pictures and know before you buy.

If there is a wide flange that sits OUTSIDE the lens mount opening of the camera, then that adapter won't allow infinity focus. If the adapter sits entirely WITHIN the camera mount and is flush with the surface of the lens mount, then it WILL allow infinity focus.

No infinity focus:

Metal Mount M42 to Pentax PK Mount Lens Cam Adapter - eBay (item 150455493326 end time Jul-14-10 05:34:35 PDT)

Allows infinity focus:

Adapter For Screw Mount M42 Lens to Pentax SLR/DSLR - eBay (item 170423473360 end time Jun-21-10 00:36:55 PDT)

Notice that the second one is not as large in diameter as the first. That is the flange. On an adapter to allow M42 lenses to be used on Canon cameras, this is okay, since the Canon mount-to-sensor distance (registration distance) is shorter than on Pentax. I don't know why these are even made this way for Pentax.

I have removed the spring clip on my third-party adapter, so it stays on my 50mm, f/1.4 Super Takumar. Friction is more than enough to keep the adapter firmly mounted in the camera and the lens firmly mounted in the adapter. I've never had the lens come loose or fall off in use.

Some will recommend using only the genuine Pentax-brand adapter. They are more expensive (about $35) but are supposedly of higher quality. I have a third-party adapter and I have never had trouble with it.

06-18-2010, 11:02 AM   #5
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QuoteOriginally posted by GregX999 Quote
Hi all,

A few questions regarding M-42 lens adapters (for a K-7):

1. Are the ones on e-bay that say "allows infinity focus" just as good as Pentax ones? I see some listed for like $5-$10. I did find some info saying they may not be machined as well as the genuine one, but is that important if I want to do number 2 below?

2. Can they be mounted on the lens instead of the camera? (So when you remove the lens from the camera, the adapter stays on the lens.)

3. Do any exist that allow auto-apeture (shutter-priority)? I assume not.

Thanks!
Greg

this topic comes up often and as i was once in the camp of those who require the PENTAX official adapter, I have since tried one of the $7 chinese infinity focus rings and it is a great bargain. It actually fits more snugly than the official adapters so the lens does not have any tendency to back itself off the camera mount when aggressively focusing. once this happens with your heavy tele lens, you will appreciate such a feature.
Also, on the ones i got, infinity focus is not affected in any way.

Because i do not dedicate a camera exclusively to screw mount lenses, i must switch between K mount lenses and M42's. Thus, it is not practical for me to ever want to mount an adapter to the camera and have the spring engage. So, i dedicate an M42 adapter for each lens and screw it very tightly so it does not come off easily. Some recommend glueing, but i haven't brought myself to trying that yet. Anyway, if you have a ring for each lens, you would remove the little spring latches off the adapters. that's how i do it.

Another benefit of the $7 ring is that it does not wobble in the camera mount like the Pentax rings do...if you have a lens with a very narrow base such as the Helios 44-2 where this wobble is apparent, the cheap adapter solves that problem too.

the only drawback i have found with the $7 adapter is that when the lens is mounted, the markings do not position under the flash overhang but are a few degrees before 12 o'clock (if that makes any sense). this would equate to a preference thing only, as it does not affect the operation of the lens. Somebody suggested applying some clear nail polish to get just the right positioning, but i havent tried that.
06-18-2010, 11:47 AM   #6
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QuoteOriginally posted by mikeSF Quote

Another benefit of the $7 ring is that it does not wobble in the camera mount like the Pentax rings do...if you have a lens with a very narrow base such as the Helios 44-2 where this wobble is apparent, the cheap adapter solves that problem too.
Really? I suffer from 44-2 wobble, but never knew a cheap ring could fix this.

What the heck--I'm learning to like the wobble.
06-18-2010, 06:26 PM   #7
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Thanks all! Great info!

I did just find a blog of someone who dremelled a notch in their lens after attaching the spring-less adapter so it "locks" in place. Not sure I want to do such a thing, so it's good to know that friction should hold them okay.

Greg
06-20-2010, 12:04 AM   #8
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QuoteOriginally posted by Ira Quote
Really? I suffer from 44-2 wobble, but never knew a cheap ring could fix this.

What the heck--I'm learning to like the wobble.
indeed, comparing both, the pentax rings have some play and the cheapies are tight.

QuoteOriginally posted by GregX999 Quote
Thanks all! Great info!

I did just find a blog of someone who dremelled a notch in their lens after attaching the spring-less adapter so it "locks" in place. Not sure I want to do such a thing, so it's good to know that friction should hold them okay.

Greg
yes but not many have a wide enough base to reach the pin. I have very few M42s for which a notch would work.

06-20-2010, 08:17 PM   #9
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QuoteOriginally posted by GregX999 Quote
Hi all,

3. Do any exist that allow auto-apeture (shutter-priority)? I assume not.

Thanks!
Greg
Auto aperture is not the same as shutter priority. In M42 terms, auto-aperture refers to the camera's ability to push the little pin to stop the iris down to working aperture just before exposure. Contrast this to cheaper lenses of the day, which were often "preset". On a preset lens, there are two rings. One ring has the familiar detents or click stops for the various aperture settings. The other ring is free moving and stops the aperture down until it hits the stop you have selected. In operation, you set the aperture on the first ring, while keeping the aperture open. You then put the camera to your eye, focus and compose. Then, turn the free moving ring to the working aperture and release the shutter.

AFAIK, there are no M42/K adapters that allow auto-aperture operation. First the k-mount cameras, including all the dslrs, have no way of operating the stop-down pin on an M42 lens. One problem with trying to do so is that the M42 lenses are normally open until the camera pushes the pin to stop them down. K-mount lenses (and therefore K-mount cameras) work just the opposite. The lens is stopped down, unless the camera holds the aperture open. This is why an M42 lens stays open when removed from the camera, while a k-mount lens stops-down.

Shutter priority is not possible, because, even on the Super-Multi-Coated or SMC Takumar lenses, there was no way for the camera to set the aperture. The later lenses could inform the camera of the aperture that the user had selected on the aperture ring, but no way to do the reverse.
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