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Pentax K lens -> m42 mount conversion
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PostPosted: Thu Oct 16, 2008 8:39 am    Post subject: Pentax K lens -> m42 mount conversion Reply with quote
Anyone done that? Register distance is the same but are there parts that can't be removed?

Do you think we should have "avant-garde" area for all kinds of experiments? Rolling Eyes

Last edited by kansalliskala on Thu Oct 16, 2008 11:09 am; edited 1 time in total


PostPosted: Thu Oct 16, 2008 10:16 am    Post subject: Reply with quote
You could just use an adapter....


PostPosted: Thu Oct 16, 2008 11:09 am    Post subject: Reply with quote
Sorry, I was vague.

I was thinking that I take Pentax K-lens, grind the back off and put m42 thread there. The obvious difficulty is if the aperture mechanism springs and cogs fly to different directions during operation.


PostPosted: Thu Oct 16, 2008 12:01 pm    Post subject: Reply with quote
Hi, the aperture arm broke off from my smc Pentax-M 1.7/50 and I took off the chrome backplate to try to fix it. I think it would be perfectly possibly to replace the backplate with an old M42 plate drilled to fit the screwholes. The projecting shield round the rear element is fitted to the backplate so this would disappear.

As for the aperture control, the control ring has a groove on the inside that fits over an arm connected to the blades, so this has to stay. This arm is L-shaped and has a part pointing back towards the camera which goes through a slot in the backplate, so it would be necessary to file this down to clear the underside of the plate. There is another longer arm (which broke off my lens) which would need to be removed. This is rivetted to on a plate inside the lens and could be drilled out (if it won't break off like mine!).

Do you need any pics?


PostPosted: Thu Oct 16, 2008 12:41 pm    Post subject: Reply with quote
Xpres wrote:
You could just use an adapter....

I don't think that there is an adapter to turn a PK-lens into an M42-lens, just the other way around.


PostPosted: Thu Oct 16, 2008 1:15 pm    Post subject: Reply with quote
LucisPictor wrote:
Xpres wrote:
You could just use an adapter....

I don't think that there is an adapter to turn a PK-lens into an M42-lens, just the other way around.


You're right... the original post is clear now, I misunderstood.


PostPosted: Thu Oct 16, 2008 1:26 pm    Post subject: Reply with quote
peterqd wrote:

As for the aperture control, the control ring has a groove on the inside that fits over an arm connected to the blades, so this has to stay. This arm is L-shaped and has a part pointing back towards the camera which goes through a slot in the backplate, so it would be necessary to file this down to clear the underside of the plate.


Is this the "auto" connection that shuts the aperture by some spring mechanism or does it actually move the blades?

Do you have a picture with the backplate off?

Thanks!


PostPosted: Thu Oct 16, 2008 2:05 pm    Post subject: Reply with quote
kansalliskala wrote:
peterqd wrote:

As for the aperture control, the control ring has a groove on the inside that fits over an arm connected to the blades, so this has to stay. This arm is L-shaped and has a part pointing back towards the camera which goes through a slot in the backplate, so it would be necessary to file this down to clear the underside of the plate.


Is this the "auto" connection that shuts the aperture by some spring mechanism or does it actually move the blades?

Do you have a picture with the backplate off?

Thanks!


The auto feature of PK lenses works in reverse to M42 lenses. Instead of the aperture blades being held open by a spring, as on an M42 lens, on a PK lens the spring tries to keep them closed down. When the lens is mounted on the camera, the longer arm (the one that broke off my lens) holds the aperture open against the spring until the shutter is fired. But when the lens is not mounted and the arm is free, the spring closes the aperture down to the f-setting of the dia ring. You can try this by hand. Therefore the lens would function OK without the long arm, but in stop-down mode only.

The other arm is more difficult to see. It's inside the long slot on the opposite side of the rear element to the long arm. It doesn't project beyond the plate, but it will prevent the new backplate from seating properly unless you shorten it or cut a new slot. This is the L-shaped one I described and the other end of it sits in a slot on the inside of the dia ring. It's not directly connected to the blades, but acts as a stop for the spring, and without it the spring would close the aperture right down. That's why I said it has to stay.

I'll do some pics for you shortly, backplate removed. I bought a direct replacement for this lens but it had fungus, so I swapped the glass over. The pics will be of the old body with the fungus glass. Wink


PostPosted: Thu Oct 16, 2008 2:37 pm    Post subject: Reply with quote
OK, here is the PK mount before disassembly:


The chrome backplate is fixed with 5 crosshead screws and just lifts off. Note that the black insert surrounding the rear element, including the projecting shield, is fixed to the backplate:


With the plate removed you can see the shorter arm on the left, connected to the dia ring. This needs to be shortened. The longer arm (see the first pic) would normally be mounted by the two stubs of rivets you can see on the right hand side. On this lens the arm has broken off.


PostPosted: Thu Oct 16, 2008 5:03 pm    Post subject: Reply with quote
Bigger problem might be the diameter of back lenses - that is one reason why they switched to bayonets.


PostPosted: Thu Oct 16, 2008 7:26 pm    Post subject: Reply with quote
The outside diameter of the rear lens in the picture is 34.1mm. The removable M42 mount on a Jupiter-37A has 37.2mm internal diameter


PostPosted: Fri Oct 17, 2008 6:31 am    Post subject: Reply with quote
Just curious...what lenses are you looking at in K mount that you can't find in native M42?


PostPosted: Fri Oct 17, 2008 9:35 am    Post subject: Reply with quote
That is not the point. My idea is more star-trek-like-assignmet "to adapt any lens to any kind of mount". Smile


PostPosted: Fri Oct 17, 2008 5:10 pm    Post subject: Reply with quote
kansalliskala wrote:
That is not the point. My idea is more star-trek-like-assignmet "to adapt any lens to any kind of mount". Smile

More like "Mission Impossible"! Smile Were the pics helpful?


PostPosted: Sat Oct 18, 2008 9:52 am    Post subject: Reply with quote
Yes, thank you, they were most informative!

Actually they seemed the task more possible than I first thought. Idea


PostPosted: Fri Oct 31, 2008 3:26 pm    Post subject: Reply with quote
kansalliskala wrote:
Yes, thank you, they were most informative!

Actually they seemed the task more possible than I first thought. Idea


I know none Pentax K lens that need the mount to work. I mean the aperture ring can still open or close the iris blades at the right values even if the metal bayonet mount is removed. This is not the same deal with third party PK lenses.

Dismantled SMC Pentax-M lenses so far : 28/2.8; 28/3.5; 35/2.0; 40/2.8; 50/1.7; 135/3/5


PostPosted: Thu Nov 06, 2008 9:24 am    Post subject: Reply with quote
Third party lens(es) are even easier. Here is Makinon 35-70. The whole mount and all the levers were attached to the same module. Obviously because one can use the same lens for several mounts.



Now the task is just too simple, just grind and drill the donor mount. But I don't know any more if I want to do that. The lens itself is crap and there is a hair or scratch inside so there is no great practical use? First I thought I could use it as some sort of "emergency" lens with Zenit in environments where I don't want to go with my russian lenses such as rock climbing and sportsbars.

It might be more interesting to just disassemble it to see how zooms work?
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