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There are two types of M42-to-K-mount adaptor:

• The Flange type
• The Recessed type

Don't be like me and get the wrong type, which is the Flange type. While the flange type is cheap, is commonly available and the flange appears thin, it is still thick enough to prevent focus at infinity.

Get the recessed type. I've got a "Roxsen" 3rd-party version. This is very easy to fit on a K100D Super body, but I find it is difficult to fit or remove this quickly on a K20D. The genuine Pentax M42 recessed adaptor is reported to be easier to fit compared to 3rd-party adaptors.


Here's some pictures I took showing the difference between the two M42-to-K-mount adaptors.

Recessed-type adapter plus insertion/removal key on left – Flange-type on right. Both showing the side that fits to the camera:



Flange-type fitted:






Recessed-type fitted:


Dan.

[vonBaloney]

Good point. No doubt it is just as confusing for them. This particular one was priced quite high so I thought it may have been a genuine.

A copy got stuck on my camera once so I am keen to get a genuine now if I can but the prices for new adapters are just crazy (eg BH Photo are selling them for US$75).

Like I say in my earlier posts in this thread, if it ain't the real one, take that spring off immediately and never look back. If you aren't sure whether it is genuine even after it is in your hands, take the spring off and put it on a body -- the real one will be pretty loose and move around, the fake ones will stay in there pretty firmly even without a spring. (If it is the real one, put the spring back on.) In practical usage, real ones go on the body and stay there, fake ones go on the lens (sans spring) and stay there.

[stillshot2]

Can anyone comment on how much focus is lost with the non-infinity focus-able adapters? For example, will I still be able to focus out to 50 feet away or does it become a strictly macro only lens with such adapter?

[vonBaloney]

Can anyone comment on how much focus is lost with the non-infinity focus-able adapters? For example, will I still be able to focus out to 50 feet away or does it become a strictly macro only lens with such adapter?

Depends on the lens -- 50ft *IS* infinity with many lenses. It is always closer than I want it to be though (with anything that isn't a macro already) so I don't like those adapters, but again, just depends -- with a telephoto you can get 10 or 20ft probably, but if you are trying to focus at near the limit it is just going to annoy you to no end. (Some adapters are thinner than others -- look for a flimsy-looking one if you get one.)

[stillshot2]

Depends on the lens -- 50ft *IS* infinity with many lenses. It is always closer than I want it to be though (with anything that isn't a macro already) so I don't like those adapters, but again, just depends -- with a telephoto you can get 10 or 20ft probably, but if you are trying to focus at near the limit it is just going to annoy you to no end. (Some adapters are thinner than others -- look for a flimsy-looking one if you get one.)

Ok thanks. I've also been thinking about readjusting the focusing range of the lens to go past infinity so with such adapter would end right at infinity but I'm not that knowledgeable on how to disassemble lenses in order to do so. I just want a permanent mount for a Takumar 200mm f5.6 and don't like the ones with the removable tabs so much..

[vonBaloney]

Ok thanks. I've also been thinking about readjusting the focusing range of the lens to go past infinity so with such adapter would end right at infinity but I'm not that knowledgeable on how to disassemble lenses in order to do so. I just want a permanent mount for a Takumar 200mm f5.6 and don't like the ones with the removable tabs so much..

Well... good idea to learn to like them -- just stick it on there (remove spring on adapter) and make it a semi-permanent bayonet. I've got at least a dozen like that -- the friction fit is usually more than adequate as long as you don't forget that's how it is attached (and your focus isn't so stiff that it rotates the lens off the camera).

[photoptimist]

Can anyone comment on how much focus is lost with the non-infinity focus-able adapters? For example, will I still be able to focus out to 50 feet away or does it become a strictly macro only lens with such adapter?

The formula for the maximum focus distance is a very strong function of focal length. The formula is:

MaxDist = f*(2+f/∆+∆/f), where ∆ is the flange thickness in mm and f is the focal length in mm

So, if the flange is 1 mm thick, the maximum focus distance for some different lenses would be:

28mm: 2.8 feet
50mm: 8.5 feet
100mm: 33.5 feet
200mm: 132 feet

Note that these numbers change a lot if the lens can focus past infinity.

[stillshot2]

the friction fit is usually more than adequate

Sadly, the focusing ring on this lens is just a little too stiff for the mount to have a good enough friction fit. I do have two other lenses that work ok with the infinity adapters attached and with the springs removed though.

200mm: 132 feet

Thanks for the calculations! I think 132 feet could be enough for me. May try it out

[Oktyabr]

Don't the flange type short the pins, allowing CIF?

[Mister Mike]

Don't the flange type short the pins, allowing CIF?

You're right about that -- that's the one shortcoming of the good Pentax adapter. I hat to rig a separate tinfoil setup to short the pins for lenses that didn't do it on their own, like an Industar that was too narrow to touch the pins.

[Oktyabr]

I just bought a Helios 44-2 2/58mm and it's too narrow with an "infinity" adapter as well. Ordered the "wrong" type of flange adapter, which I plan to just leave on the lens, so I can have CIF.

[RocksandRocks]

Has there been any new developments on adapters? I just acquired a yellowed takumar 50mm 1.4 and I didn't realize that the genuine adapters are 100 bucks on B&H! I would like to use it on my kp, so I don't want the flange mounted permanently to the camera, but mounted on the lens. Is there a better, cheaper solution now?

[vonBaloney]

Has there been any new developments on adapters? I just acquired a yellowed takumar 50mm 1.4 and I didn't realize that the genuine adapters are 100 bucks on B&H! I would like to use it on my kp, so I don't want the flange mounted permanently to the camera, but mounted on the lens. Is there a better, cheaper solution now?

Buy the cheap knockoffs of the genuine one (with no flange so you get infinity focus), remove the little spring before you ever use it (or else you are in danger of being driven insane when it gets stuck on camera), and then you just leave it on the lens. (The genuine one is not good for leaving on the lens btw). The only drawback is you've got a friction fit to the body now which is usually fine but if your old lens is stiff, sometimes it will turn out of the mount when you are focusing which could lead to disaster. (Usually you're using m42 lenses in a pretty deliberate way, but you do need to be careful with that.) I've got a whole cabinet of m42 lenses I use in this style.

[que es tu]

Has there been any new developments on adapters? I just acquired a yellowed takumar 50mm 1.4 and I didn't realize that the genuine adapters are 100 bucks on B&H! I would like to use it on my kp, so I don't want the flange mounted permanently to the camera, but mounted on the lens. Is there a better, cheaper solution now?

You can watch for a genuine Pentax one to be put up for sale here on the Marketplace by a PF member. I have seen some over the past year for an average of $30 or so.

[photogem]

Buy the cheap knockoffs of the genuine one (with no flange so you get infinity focus), remove the little spring before you ever use it (or else you are in danger of being driven insane when it gets stuck on camera), and then you just leave it on the lens.

That's how I do it with many M42 lenses, but:

The genuine one is not good for leaving on the lens btw

Why would that be?
I have 2 genuine ones which I leave always on my Takumar 50/1,4 (8-element) and on my Takumar 85/1,9.
It works fine but of course these days is a bit of an expensive solution (I got mine much cheaper long time ago)

There are better ones than the cheap modern China-versions though!
One was offered by Hama (it was made in Japan but this is not mentioned in offers)
and quite a few other ones made in Japan (those usually have M42 + Japan printed on it):
pentax m42 adapter for sale | eBay

The only drawback is you've got a friction fit to the body now which is usually fine but if your old lens is stiff, sometimes it will turn out of the mount when you are focusing which could lead to disaster. (Usually you're using m42 lenses in a pretty deliberate way, but you do need to be careful with that.) I've got a whole cabinet of m42 lenses I use in this style.

One possibility is to use that tiny screw which held the spring to fix the adapter on the M42 thread.
The other option of course would be to use some glue.


A great way to do it including the correct position-stop is explained here in This thread which I just opened.
It is a translation from the German tutorial to English.

[vonBaloney]

Why would that be?
I have 2 genuine ones which I leave always on my Takumar 50/1,4 (8-element) and on my Takumar 85/1,9.
It works fine but of course these days is a bit of an expensive solution (I got mine much cheaper long time ago)

With the genuine ones, you really need to leave in the spring/lock because they are much more loose in the mount than the knockoffs. And if you leave the spring in, you've got to unscrew the lens from the adapter to get it off the body. Anyway, with my genuine ones, I use them as they were designed -- as *body* adapters not lens adapters -- they just work better that way.

However, the knockoffs are always way tighter and if you leave in the spring THEY WILL GET STUCK at some point. So with those I take the spring out immediately and I just screw them on the lenses that I want to use. (But without the spring the lens is never totally locked on the body.)

One possibility is to use that tiny screw which held the spring to fix the adapter on the M42 thread.
The other option of course would be to use some glue.

Although I do "leave them on the lens", I do not lock them on the lens permanently or even semi-permanently as I have way more lenses than adapters, and there is just no need -- they don't fall off or anything. So I just mean I leave them on the lenses generally (i.e. the lenses I've got that day) and then I can mount and unmount them quickly like K-mount lenses.