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11-26-2011, 03:06 AM - 1 Like   #1
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Nikon 135mm f/2 AI adapted to PK

During the Thanksgiving downtime, I did some surgery on my newly acquired Nikon 135mm f/2. I knew from previous threads that it was possible to directly mount old F-mount lenses to Pentax cameras, but I wanted something that locked at the 12 o'clock position and had a usable focusing scale. The conversion was quite simple and is mostly reversible. The mount was removed with a JIS cross-point screwdriver (important, since the heads are NOT Phillips, and the threads are locked in place) and replaced with an aluminum spacer and PK-M42 adapter. The spacer and mount flanges combined were about 0.95mm thick, so the lens focuses a tiny bit past infinity. Here's a comparison with a C/Y Planar 85/1.4 and a Nokton 58/1.4. In the last picture, you can just make out the aluminum spacer and brass flange. These were simply glued together with metal cyanoacrylate. All of the "machining" was done with a jeweler's saw and a Dremel tool. The AI-indexing ridges were filed down just a hair (less than a millimeter) to get the lens to sit flush with the camera-side mount.

Here are a couple of images from the lens, both at f/2. I haven't had much time to shoot with it due to the typically rainy Portland weather.

It is quite sharp wide open, but suffers from purple fringing and a "glow" under high-contrast situations (kind of what you expect with long, large aperture lenses, though). Sharpness doesn't improve much upon stopping down, but contrast and PF issues improve by f/2.8 or f/4. The defocusing characteristics are generally very creamy, except for bright point highlights. For the record, my girlfriend thinks that it's the ugliest lens she's ever seen

I'd like to convert more Nikon lenses by replacing the lens mounts with a spacer and a Pentax bayonet. This method is more labor intensive, but is cleaner and more secure. Maybe a 35/1.4 or a 28/3.5 shift would be next

11-26-2011, 04:10 AM   #2
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Great job!!! nice pics.
11-26-2011, 04:44 AM   #3

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Good job done!
11-28-2011, 11:10 AM   #4
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11-29-2011, 02:20 AM   #5
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Thanks for the kind words everyone! I hope to have more photos with the lens once my K5 comes in the mail
11-30-2011, 11:33 AM   #6
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QuoteOriginally posted by dcshooter Quote
The lens might be ugly, but your girlfriend is cute!

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