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03-08-2009, 06:33 PM   #1
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Lens Mod Possibility?

Yo! I have this nice F-mount lens, a Nikkor 85/2, serial 251228. Great smooth focus, and easy yet firm aperture detents. I can just force-fit it onto my K20D without damage - start with the tongue at 6 o'clock, jiggle clockwise firmly - but it's not exactly a reliable fit.

The Nikon flanged bayonet ring attaches to the bottom of the lens with 3 small screws (aimed down) and 3 tiny screws (aimed in). I am sorely tempted to try to pull off that bayonet ring (if I can get it unscrewed - my cheap 'precision' screwdrivers are a bit too large and soft) and replace it with a flanged M42-PK adapter ring, which looks like it will be a good fit.

My question, before I clumsily turn something that works somewhat into something that won't work at all, is: Does anyone here have experience with such surgery, or know of any online descriptions / instructions? I'm aware that there will be 'issues' over the aperture stop-down tab, which moves in the opposite direction of a Pentax. But I could use some advice here.

It would be great if I could turn this into a Niktax (Penkon?) chimera. My only other 85/2 is an M39 Jupiter-9, which weighs 50 g more and is rather stiffer to focus. I'd use the Nikkor more if I knew it wasn't about to fall off the camera, eh?

03-08-2009, 07:20 PM   #2
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QuoteOriginally posted by RioRico Quote
My question, before I clumsily turn something that works somewhat into something that won't work at all, is: Does anyone here have experience with such surgery, or know of any online descriptions / instructions?
Check out Sean Carpenter's posts on dpreview:

Using Nikon F Lenses On Pentax K Bodies (LBA Post): Pentax SLR Talk Forum: Digital Photography Review
03-09-2009, 04:10 PM   #3
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Normally the bayonet mount comes of quite easily and there is nothing attached to it (I am not completely sure for this lens, though) but you should get a good fitting screwdriver since the screws are hard to come by.
I am not sure if the flanged m42 adapter will fit, it might be to thin, but you will see after you removed the mount. It has to be thick enough so that the screw fit in flush. Another option is to use the mount of an old cheap pentax lens.
I did something similar with topcon lenses, you can see a description here:
Converting Topcon lenses to Pentax K

Chris
03-09-2009, 06:35 PM   #4
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I've changed a non-AI nikon lens to a fully manual K lens mount.

Remove the nikon lens' bayonet plate. Be careful, some non-AI lenses have a plate which cannot be removed without completely disassembling the lens - such lens have no screws showing in their base - avoid them.

I just cut off the lens' stop down lever - it is easy to use the lens in fully manual mode on a pentax camera.

Replace the nikon flange base with a flanged-type m42-Pentax K adapter. I drilled holes in it and reused the nikon screws. The diameter of my m42 adapter was a little too large and it had to be decreased to about 57.5mm to fit into the nikon lens base's recess.

03-10-2009, 10:05 AM   #5
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newarts, how did you adjust the diameter of the m42 adapter -- lathe?

I'd like to try something like this, but I don't have any metalworking equipment (unless a Dremel tool counts) and I wonder how feasible it is with just hand tools.
03-12-2009, 09:02 PM   #6
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Original Poster
Thanks for the suggestions and links. I twisted the Nikkor on a little tighter, and it holds, but I'm still exploring the bayonet-change possibility. I just have to find the right tools, which isn't easy out here in the hinterlands. We'll see...
03-12-2009, 11:23 PM   #7
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Why not drilling a small hole in the flange of the Nikkor lens for the locking pin on the camera? If the lens does not rotate, it will not come out.

Some Nikon-F lenses can be made into screw mount. Some can't without too big of a risk.

Here's my latest found:

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