[bobtheicicle]

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I recently picked up a good condition Takumar 300mm f4 screw mount lens (the original 3-element version). I'm using a genuine Pentax M42 to K mount adapter, but when I screw the lens in, the adapter doesn't lock into the camera. Specifically, the focusing ring is slightly stiff on the lens (but not stuck) and simply adjusting the focus can unseat the adapter (which can cause the lens to separate from the camera body, with a potential for disaster).

The adapter sticks to the lens and takes significant effort to remove manually (or I can remove it easily by simply attaching it to my k1000, where the adapter seats properly and pulls it right off the lens as easily as I'd expect).

I didn't anticipate this problem at all, as the adapter works perfectly with my Takumar 50 f1.4. It remains locked into the K-3 or K-01 exactly as I'd expect, and I unscrew the lens before removing the adapter.

I've tried mounting the adapter to the lens first, and to the camera body first. Either way, it sticks to the Takumar 300mm lens's threads and unseats from the mount without much in the way of resistance. I do hear/feel two very faint clicks as it unseats, which I think might be the locking pin moving over the screw holes on the back of the mount.

The most perplexing thing is that it works so well on the K1000, but not the K-3 or K-01. Anyone else encounter a similar problem? Any suggestions?

[BigMackCam]

Is the aperture control "pin" particularly long on the Takumar 300? I have a Russian Jupiter-21M 200mm lens, and the aperture pin is longer than on any other lens I own. I found that it will foul the SDM contacts just behind the camera mount - so much so that on my K-5 I actually scraped a groove into both of those contacts as I was mounting and removing the lens. That could possibly be the issue here? You would get that faint double-clicking sound as the pin passes over the SDM contacts...

The solution for me was to use an M42 adapter by Kipon. It has an inner flange that pushes in the aperture pin as you screw the lens into the adapter...

[D1N0]

The adapter doesn't really lock in very well. With smooth small primes that isn't a problem. Big tele's with large diameters can turn it out easily. I guess digital bodies are not entirely compatible with the adapter. I can turn it out while attached to the lens, but not on the k1000 as well. Maybe there is a difference between analog and digital age m42 adapters? Mine came with a K1000 on which it sticks. on my K-5 it can come of, just like the third party ones from which I removed the spring.

[bobtheicicle]

The 3-element version of the Takumar 300/f4 doesn't have an aperture control pin or switch - only strictly manual aperture.

I appreciate the response!

---------- Post added 09-09-16 at 07:52 AM ----------

D1N0, glad to hear this isn't a problem unique to that lens. I just wish there were a good solution, as it makes this lens even more a tripod-only lens (so that the torque on the lens from turning the focusing ring will be transfered to the tripod mount and not the lens mount).

[Audi 5 cyl]

I've been using the Chinese adapters almost exclusively and had issues with only one out of twenty or so that I own. Still, knowing that some people had problems with it, I won't be sending you down that path. Did you try to unscrew and re-screw the locking mechanism? Does it look bent in comparison to the pictures of the new product online?

Edit: You can also try to clean the helicoid, and re-grease it with a lower viscosity product. For my old CZ heavy 300mm Sonnars, this is what worked, with a "normal" grease they have been very difficult to handle.

[Quartermaster James]

For the record:
The Pentax Mount adapter K is not intended to be installed on the lens.
It is intended to change the camera body to accept the M42 lens.
The correct procedure is to fit the adapter to the body and to then mount the lens to the body.

That said (yes, I read you have tried both ways) it sounds like there may be damage to the threads on your lens. Maybe residue from someone previously gluing a mount onto it, maybe damage from cross threading.

I use this lens on my K30/K3/K3ii with no similar problem, also using the Pentax Mount adapter K.

[stevebrot]

I've tried mounting the adapter to the lens first, and to the camera body first. Either way, it sticks to the Takumar 300mm lens's threads and unseats from the mount without much in the way of resistance. I do hear/feel two very faint clicks as it unseats, which I think might be the locking pin moving over the screw holes on the back of the mount.

Well, that is strange. As I read it, you are saying that the spring clip is not properly retaining the adapter in the mount. The most likely explanation is that your adapter may be broken, defective, or worn-out.

Question: Does the mount face on the adapted lens fully engage the face of the K-mount? The lens should "snug up" to the body as it mounts. This should be the case regardless of whether you put the adapter on the lens or on the camera first.* If the lens does not "snug up", the adapter and attached lens will tend to "rock" in the mount (the tangs in the body are spring-loaded). This is not uncommon with some European and Soviet lenses and (by report) some early Takumar lenses. It is possible that if the lens adapter is "sagging" in the mount, the spring clip may not align properly with its catch.

You may also want to look into re-lubricating the focus mechanism so that it presents less resistance. While having the adapter spring fail is one thing, the more common case is that the lens unscrews while focusing. Not good.


Steve

* I have no desire to contradict Jim's comment above, but directions for use of the genuine K-mount adapter have varied over the years. I have two and both came with instructions to mount to the lens first. The manual for my KX film camera also says to mount to the lens first. OTOH, the manual for my Super Program says to insert the adapter in the K-mount first and screw the lens on to mount. The advantage to the former is that it is much easier with large lenses. The advantage to the latter is that any impediment to a clean dismount will be evident on observation. (There are rare corner cases where a lens may mount cleanly with the adapter on the lens only to jam when unscrewed. I recommend using the screw onto body technique with all new lenses, while carefully taking into account any pins or protrusions that might cause problems.)

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Last edited by stevebrot; 09-09-2016 at 09:10 AM.

[marcusBMG]

I can mention (once again) that there is a lot to be said for using a flanged adapter in these circumstances. yes that will stymie your putative moon shots because you will lose infinity focus, but you will still be able to focus to about 200m (based on quick test with one of my adaptall 300mm + M42 mount + flanged adapter on G1) - surely covers 95% of what you want to photograph. Screw it on tight, use a few paper shims or a bit of insulating tape if you want to provide "lock" and to orient the lens at 12 O'clock. Lens is then like eg a t-mount lens and the locking pin on the mount holds it in place.
(the holes in mine are from its use in a mount swap project)

[Quartermaster James]

FWIW, I am citing the instructions that came with my adapter. My apologies if Pentax has been inconsistent with these. I was unaware of that before Steve enlightened me.

[bobtheicicle]

Audi 5 Cyl, any suggestions for a lower-viscosity lubricant?

Quartermaster James, I've inspected the threads and didn't see any obvious damage or residue. It is possible that in the history of the lens someone tried to mount a T-mount adapter (also 42mm, but different thread pitch - which would mess with the threading).

Stevebrot, The lens is snug against the K-mount when fully mounted. I cannot extract or rock the lens except by turning it (which disengages the adapter from the K mount). I'll check the retaining spring for damage or bends, but it is odd to me that it works well on the K1000 but not the newer digital bodies. This adapter is also an older, used item, so a thorough inspection against a reference image or item is probably called for.

[swanlefitte]

I don't see why the screwing in of the lens would disable the locking pin if it was ever locked in unless the adapter was warped somehow. Mine works on my MX and k-s2 just fine. See that the lock is screwed on tight to the adapter too. Check out this thread for reference pictures. https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/323690-original-asahi-pentax-adapter-stuck-k-s2.html

[tim60]

I have this lens and use it on my K3.

I have two adapters, the one I normally use has the spring clip in good condition and it locks in properly. I mount the adaptor int he body and use it like a screw mount body.

The other adapter has had something happen to the spring clip that results in it sometimes coming loose like you describe. I tried attempting to twist the bad spring clip with pliers but have not got it right.

[Quartermaster James]

Audi 5 Cyl, any suggestions for a lower-viscosity lubricant?

Quartermaster James, I've inspected the threads and didn't see any obvious damage or residue. It is possible that in the history of the lens someone tried to mount a T-mount adapter (also 42mm, but different thread pitch - which would mess with the threading).

Stevebrot, The lens is snug against the K-mount when fully mounted. I cannot extract or rock the lens except by turning it (which disengages the adapter from the K mount). I'll check the retaining spring for damage or bends, but it is odd to me that it works well on the K1000 but not the newer digital bodies. This adapter is also an older, used item, so a thorough inspection against a reference image or item is probably called for.

Okay then. Sorry. Looks like you've stumped the band with this one!

[D1N0]

or I can remove it easily by simply attaching it to my k1000, where the adapter seats properly and pulls it right off the lens as easily as I'd expect

This is the key. The adapter sticks in the K1000, not in the K-3 or K-01. I have a similar experience. So there is something different in the digital bodies causing the adapter not to stick properly. I can hear a click but when the lens is on tight enough the adapter will just come out with another click. The question is, is there a difference in adapters and or bodies between digital and analogue?

[stevebrot]

The question is, is there a difference in adapters and or bodies between digital and analogue?

Quite possible. Despite conventional wisdom, K-mount implementations are not fully standardized even within the Pentax brand. For example, there are a significant differences (flange width/thickness and body clearance, for example) on the camera side between the K-series and A-series bodies film bodies. That being said, I would expect a high degree of conformity for KAF2 and later variants because of the multiple points requiring precision positioning (specifically, AF drive and power contacts) regardless of whether those bodies contain a digital sensor or 35mm photographic film.


Steve