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04-10-2011, 02:48 PM   #1
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mamiya/sekor21mmf4. sx lens modification

ok,i want to use a mamiya/sekor 21mm f4.0 SX , lens on my pentax k10D camera.
i did remove the outer aperature control pin. if i grind down 2mm looks like of the cowl end of the arerature ring,will it allow the lens to fully screw into the now seems to only screw in about 80% of way,still need it to turn in 1 full turn.dont want to ruin looks of lens if this grinding will not allow lens to thread in fully.or is it possible to take a adapter and grind it down thinner so lens gets in deeper to camera/ any help appreciated.achually it seems the back of lens aperature ring is hitting the camera base not the adapter.

Last edited by bobwells; 04-10-2011 at 03:19 PM.
04-22-2011, 03:13 AM   #2
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I must say that I am not familiar with SX lenses. But I have read that SX adapters are available for various camera mounts. I don't know how these differ from ordinary M42 adapters. But I *do* have a trick for bring a screwmount lens closer to the sensor, deeper into the camera body:

Take a cheap Bower-type M42-PK adapter. REMOVE THE SCREW AND CLIP! Tape a sheet of 100-grit or other rough sandpaper to a very flat surface, like a smooth ceramic tile. Put the adapter on the sandpaper with the wider flange-side DOWN, against the sandpaper. (The flange is what sits against the lens body; the other side fits into the camera mount.) Use a block of rubber (like a large pencil eraser) to hold the adapter, and grind away that flange! The flange is just about 1mm thick. About half that thickness can be removed without weakening the adapter too much.

I have done this with adapters to allow seating Exakta-mount lenses on my K20D, to reach infinity focus. I don't know that this will solve your Mamiya SX dilemma, but it's the best I can suggest. Good luck!
04-23-2011, 06:40 AM   #3
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mamiya/sekor adaption

i found the cheap adapters come in all diffrent thicknesses,no quality control at all.sandind down if lens does not have the cursor focus mark come srraight up 12:00 does help. i took chance did grind down the aperature ring a cowl like design,so now the base on the back of lens is able to contact the base on camera,the 21mm lens achually goes to beyond infinity,as the cursor focus mark ends up at 1:00 ,beyond straight is a very sharp colorful lens.have you tried any adapting do it yourself for using nikon lenses on pentax m-42?
04-24-2011, 12:08 PM   #4
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QuoteOriginally posted by bobwells Quote
have you tried any adapting do it yourself for using nikon lenses on pentax m-42?
For M42, no. For Pentax K-mount (PK), yes. A Nikon AI or AI-S lens has two bits of metal extending from the aperture ring, what I call the "nub and arc". I use a dremel metal-cutting blade to cut those away, then smooth the bottom of the aperture ring. The lens can now be force-fit onto a PK mount. If you want a more secure fit, you can cut a small slot for the camera's lens-lock pin to fit into. I have so modified a few N/AI lenses.

I am very sure that a modification to M42 mount is not possible, not without MAJOR surgery. The inner diameter of my thinnest M42 ring is 39mm. The inner core of several Nikon-mount lenses I just measured is about 40.5mm. It just won't fit, not without machining-away some of the lens core. I am not about to try that!

Good luck.


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