Pentax 200mm f4 SMC lens tear-down (M42)

RichardJack · Jun 28, 2017

I have a 200mm SMC with oily aperture blades. Has anyone ever opened one of these lenses up? I think the approach is from the front but it would be nice getting some pointers telling me what or what not to loosen up.
thanks in advance,
Rick

flavio81 · Jun 28, 2017

RichardJack said:
I have a 200mm SMC with oily aperture blades. Has anyone ever opened one of these lenses up? I think the approach is from the front but it would be nice getting some pointers telling me what or what not to loosen up.
thanks in advance,
Rick

The whole front just unscrews, if i recall correctly. Just grab the front with your hands and unscrew it. Probably the diaphragm would be accessible afterwards.

I have a 200/4 myself and recall having cleaned it.

Fixcinater · Jun 28, 2017

Yes I just did this on a 200/4 SMC. Front unscrews and you can clean from there. Going in through the back if you want to clean both sides directly isn't too terrible either and pretty obvious once you get the small light shield off (it's glued in place).

RichardJack · Jun 28, 2017

OK...so in short I can get to the blades from the front and try cleaning it with a q-tip, the rear will be a bit more work from the rear. I was hoping to remove the blade assembly and individual blades, soaking them in acetone. Worst case...there is none. The lens is no good as is, if I fail I'll buy another lens.
It looks like I have to loosen the 3 small screws on the focusing collar before it screws off. I will very carefully give it a try.
Does anyone have an exploded view?
thanks

Fixcinater · Jun 30, 2017

You don't have to go into the back to get them clean much less removing the whole aperture assembly. Just takes longer/more iterations of cleaning to get it all worked out through the front. I wouldn't use acetone either, that's pretty aggressive. Ronsonol or naphtha would get them plenty clean and be less of an issue to the engraving paint.

Here is a section view that I know of. Don't know of any tear-down videos or similar.

anfenglin · Jun 30, 2017

Why not try the Pentax lens disassembly database?
https://www.pentaxforums.com/forums.../179884-pentax-lens-disassembly-database.html

RichardJack · Jun 30, 2017

Thank you both! The lens diagram will be very helpful. I hope to find time to get to the lens this weekend. I'll try Ronsonol first. I found the lens in the Pentax database (as expected) but the links were expired, one took me to Ebay. I think I joined that forum years back, I have to renew my password. I have the tools and with a little patience I think I can tear the lens down. Every manufacturer has their own style when it comes to lens construction, I have repaired many Rokkors and Nikkors, this will be my first Pentax telephoto.
regards,
Rick

flavio81 · Jul 3, 2017

anfenglin said:
Why not try the Pentax lens disassembly database?
https://www.pentaxforums.com/forums.../179884-pentax-lens-disassembly-database.html

Thanks you so much for this!

Pentax 200mm f4 SMC lens tear-down (M42)

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