[Laurentiu Cristofor]

once installed, it is just as easy to change Takumar lenses on a K2 as it is a Spotmatic F.

You mean "just as inconvenient". The move to K-mount wasn't made only to add electrical contacts. It is inconvenient to change lenses in the field when you have to screw them on and off. Breech lock mounts appeared and went away for the same reason. A bayonet mount was the most effective way of switching lenses - you could even do it in the dark using that white/yellow bump on the lens. Try to change an M42 lens in the dark

The criticism is not that the adapter story doesn't make it as easy to mount lenses on K cameras as on spotmatics, but that it could have allowed us to mount M42 lenses as if they were bayonet lenses, rather than bothering with the screwmount way.

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Last edited by Laurentiu Cristofor; 07-15-2011 at 12:15 PM.

[Laurentiu Cristofor]

Strange how devensive people get when asking a simple question about Pentax. It's probably just a Pentax user thing.

It's not only Pentax users. It's communication at Internet speed. Many times people respond before they understand what they are responding to. Or maybe there's an epidemic of ADHD? I don't know, but it's interesting to observe. It's like watching people talking to your shadow. Madness? This is INTERNET!!!

[Laurentiu Cristofor]

Aim the camera down when (un)screwing lenses. Metallic dust usually doesn't fall *up*.

It doesn't fall necessarily. It sticks to the adapter and falls later when it has nowhere else to go than inside the camera. And of course, when mounting lenses, it's harder to keep the camera up and watch how you are matching the threads.

This is why screwmount is dead. Being able to mount/unmount M42 lenses as bayonet lenses would have been a great feature. Canon has it I got this feature only for a mirror lens, because they focus past infinity to begin with, so I could attach to it one of those berated adapters that prevent infinity focus with regular lenses. It works so nicely now compared to other M42 lenses - and that adapter was just $12.

[Blue]

You mean "just as inconvenient". The move to K-mount wasn't made only to add electrical contacts. It is inconvenient to change lenses in the field when you have to screw them on and off. Breech lock mounts appeared and went away for the same reason. A bayonet mount was the most effective way of switching lenses - you could even do it in the dark using that white/yellow bump on the lens. Try to change an M42 lens in the dark

The criticism is not that the adapter story doesn't make it as easy to mount lenses on K cameras as on spotmatics, but that it could have allowed us to mount M42 lenses as if they were bayonet lenses, rather than bothering with the screwmount way.

Oh well, that is a different discussion then. You need to go bitch at Contax and the Germans for the m42 mount. Pentax didn't invent that. They just adopted it in 1957 in lieu of the m37 since it had the same registry distance.

Edit: I have one of these. They are nice little bodies. I like the Asahi Optical "AP', S and K better though.

http://captjack.exaktaphile.com/praktina/Contax-Pentacon%20Cameras.htm

[pacerr]

Note, that the pentax M42 mount in its final generation did require precise rotational orientation, specifically for the Spotmatic F and ES II which had open aperture metering achieved by the same aperture reading lever as the origonal K mount.

Yes, but lacking the locking notch/peg they (S-M-C lenses) required a separate tab to precisely index the lens relative to the body.

As for the precision of the flanged adaptor, its locking is just as accurate as any pentax lens.

I'd say secure rather than absolutely precise/accurate. Where an M42 thread mount (of any brand or quality) rotationally indexes on the body is determined by where the lens thread "terminates" as it's screwed into the body. Controlling that requires either an uncommonly high degree of precision in manufacturing or additional, adjustable barrel/sleeve parts, assembly/calibration steps and QA.

I've "shaved" threads on M42 adapters to index the aperture ring left or right of the flash bulge (that's intentionally using 'poor quality control'?). Most T-mount and Adaptall adapters and bellows mounts can be rotationally (mis)adjusted by the nature of their universal design.

The "radially imprecise" bayonet mount with a locking notch for indexing the lens was functionally much more versatile.

H2

[Blue]

Yes, but lacking the locking notch/peg they (S-M-C lenses) required a separate tab to precisely index the lens relative to the body.

. . .

So does the K-mount via the lever.

Edit: There were actually a few of some late Super Tak models that had the lug you are referring to as a tab. One example is the last "generation" of the Super Tak 55/1.8 with the only discernable difference from the S-M-C version being the name and maybe the coatings.

[ryan s]

It's not possible to mount rigidly those lenses (of Eastern European and Soviet origin) which have a raised "lip" on their base without compromising the ease of disassembly (above). But why would Pentax bend over backwards to accommodate lenses which were intended only to fit Praktica and Zenit cameras?

I think all it would have taken was to make the bayonet lip 1mm longer (the one nearest to the red dot) then making the edge square instead of curved (where the flange of the adapter contacts the body mount). That would still allow it to be removable without a tool...

[Blue]

I think all it would have taken was to make the bayonet lip 1mm longer (the one nearest to the red dot) then making the edge square instead of curved (where the flange of the adapter contacts the body mount). That would still allow it to be removable without a tool...

The authentic Pentax (and Asahi Optical) adapters don't require a tool, nor do the come with one nor have they ever.

[Laurentiu Cristofor]

Oh well, that is a different discussion then. You need to go bitch at Contax and the Germans for the m42 mount. Pentax didn't invent that. They just adopted it in 1957 in lieu of the m37 since it had the same registry distance.

Edit: I have one of these. They are nice little bodies. I like the Asahi Optical "AP', S and K better though.

Captain Jack's Contax/Pentacon Page

I give up. That was not the point I was making.

[Blue]

I give up. That was not the point I was making.

The problem with the m42 lenses is they lack the slot that allows the lens to be locked. The K-mount lenses actually have a slot. For an adapter to solve that, it requires a flange, but that creates the previously discussed issue of losing infinity focus. The other possibility is to get an adapter for each lens, remove the spring, and put the notch on the lens so it locks. The adapter can be attached by a mild thread lock. However, I am not going to do that because some of my lenses are things like the 8-element ST 50/1.4, early preset Takumar 35/4, early ST 28/3.5 and so forth. Asahi Optical moved to the k-mount in part for that reason. The other was for further development which has also been mentioned. So yes, I actually did get your point. However, the OP blamed Pentax for limitations with the m42 and it wasn't a bad design in during its 25 year run. With Asahi Optical, it went from preset diaphragm, to semi-automatic diaphragm, to automatic diaphragm to open aperture metering and an evolution of coatings.

[pacerr]

... The other possibility is . . . put the notch on the lens so it locks.

The problem there is that the diameter of many M42 lens bases isn't wide enough to overlap the PK latching pin; i.e., the Vivitar (Kiron) 28/2.5 is wide enough to notch. Most 49mm Super Tak lenses aren't wide enough. [Incidentally, Dremel makes a flat end-mill bit that's perfect for cutting the notch on a drill press.)

One solution that DOES work with them if you're willing to slightly modify the lens is to drill a hole in the side of the lens into which a short pin may be glued to catch on the latch pin. A drill bit and pin about the diameter of a paper clip works well here. The pin only needs to be about 3.5 mm LOA and protrudes only about 1.5-2.0 mm from the side of the lens -- just enough to catch the latch pin -- and is very unobtrusive.

A more elegant solution is to tap the hole and use a threaded stud which could be removed later and replaced with a flush-head screw to return the lens to its original 'cosmetic' appearance. I've even thought about simply putting a "peg" made of silicone sealer in the right spot as a temporary "safety notch".

Just mark the position for the stub-pin in the lens on the correct (left) side of the latching pin with the lens properly mounted on the body or you'll surely end up with two holes! Don't ask.

Unfortunately I don't have a modified lens available at the moment so I can't show a finished product but this should explain the method. BTW, that's a ZX-M body with a plastic body mount if you're wondering -- works well and shows no wear.

Having solved the safety catch problem (to my own satisfaction) I must admit I haven't bothered with it except on a few old Super Tak's that got regular exercise outdoors.

H2

[newarts]

The problem there is that the diameter of many M42 lens bases isn't wide enough to overlap the PK latching pin;...)

One solution that DOES work with them if you're willing to slightly modify the lens is to drill a hole in the side of the lens into which a short pin may be glued to catch on the latch pin. A drill bit and pin about the diameter of a paper clip works well here. The pin only needs to be about 3.5 mm LOA and protrudes only about 1.5-2.0 mm from the side of the lens -- just enough to catch the latch pin -- and is very unobtrusive.

Great idea!

Two such pins would stop the problem of over-rotating the lens.

[m42man]

I think all it would have taken was to make the bayonet lip 1mm longer (the one nearest to the red dot) then making the edge square instead of curved (where the flange of the adapter contacts the body mount). That would still allow it to be removable without a tool...

I'm not sure I described the problem very well. The "lip" I'm referring to is a slightly raised ring around the screw thread at the lens base, which means that the lens base, as a whole, isn't totally flat. This raised ring, on some lenses, makes contact with the surface of the adapter, but not the camera's mount. Since the genuine Pentax adapter is an intentionally loose fit in the camera mount (thus making it easy to remove without a tool), then the lens remains a loose fit when fitted to the camera. The only solution is to make up an annular shim, to bring the lens base height up to that of the raised ring.

On the subject of "defensive replies", I think the responses have been very polite and measured, when you consider that the opening post was highly critical of Pentax (the subject matter of all the forums on this website), on the basis of the shortcomings of a non-Pentax "counterfeit" item which has long been the subject of criticism (in this very forum).

[pacerr]

solution is to make up an annular shim, to bring the lens base height up to that of the raised ring.

Try three strategically placed "dots" of silicone sealer on the base of the lens to act as stabilizing "pillars". Set the lens base-down on waxed paper to level and setup the sealer. You may need to provide a "well" for the adapter and aperture pin to get a level base. Trim as needed.

A very thin rubber band or O-ring of the correct diameter may work with some "lipped" M42 lenses if it's compressible enough. Acts like the WR seal ring and stabilizes the mount as well.

I've used a rubber band between the adapter and the lens base to adjust the thread depth so as to rotate the aperture ring index to the 2 or 10-o'clock position for better visibility. The soft gasket still allows the lens base to seat on the camera properly for registration distance and provides a soft friction fit in the camera. Manual operation only of course.

H2

[Laurentiu Cristofor]

The problem with the m42 lenses is they lack the slot that allows the lens to be locked. The K-mount lenses actually have a slot. For an adapter to solve that, it requires a flange, but that creates the previously discussed issue of losing infinity focus. The other possibility is to get an adapter for each lens, remove the spring, and put the notch on the lens so it locks. The adapter can be attached by a mild thread lock. However, I am not going to do that because some of my lenses are things like the 8-element ST 50/1.4, early preset Takumar 35/4, early ST 28/3.5 and so forth. Asahi Optical moved to the k-mount in part for that reason. The other was for further development which has also been mentioned. So yes, I actually did get your point. However, the OP blamed Pentax for limitations with the m42 and it wasn't a bad design in during its 25 year run. With Asahi Optical, it went from preset diaphragm, to semi-automatic diaphragm, to automatic diaphragm to open aperture metering and an evolution of coatings.

Nope, you are missing the point again. The OP and my comments are about issues with adaptability of the M42 lenses specifically to K-mount. The OP would like a similar adaptability solution as he is getting on C/Y mount. I realize it may be tricky for you to detect the focus of the conversation given that several mounts are brought into discussion, but let me try to dispel your confusion - the focus is on the drawbacks of the K-mount that make adaptability of M42 lenses less convenient than on other mounts, like C/Y or Canon EF.