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03-12-2013, 04:45 AM - 1 Like   #1
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Join Date: Feb 2013
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Hello

I would like to share with you my little experience of Nikon lenses modified to Pentax mount: Nikkor AF 35-70 f:2.8 and Nikkor AF 80-200 f:2.8.
The one I am going to describe here concern the 35-70 (it is exactly the same thing with 80-200.
Caution 1: a first trial was done with an old 35-70 f:3.5 AI, excepted a lot of trouble to find a solution to modify the inner aperture linkage the result was a real mess: lot of CA at f:3.5 and 5.6 because the lenses coatings of this era do not match the digitals sensors requirements. So do not try to modify Ai or Ais lenses.
Caution 2: you need to have access to a lath and a bench drill to do what is following.

Some Nikon parts must be removed: electric connector, AF gears and aperture actuator (see pictures).

A Aperture ring must be modified to avoid interference with Pentax body, return to Nikon configuration will be not easy without a new ring.

B Mounting screws were not easy to remove without deeps marks in the screwdriver prints, I changed them for contersunk heads ones (easy to find in small quantity in scale models hobby shops). Caution: theses screws heads are 90 shaped, be sure to have the right angle tool before to machine the head recess. I did it with a 4 mm drill bit grinded to 90 ( standard drill bit angle is 120)
I forgot to tell you: screws are M (metric) 2.0 x 20mm recuted to 16 mm (M2.0 x 25 for 80-200 lense)

C This mount was made in two part:: a lath machined ring and a M42/PK adapter because it seemed to be more simple to do without access to a milling machine. You need this milling machine to do the 3 locking slots.
You will have to do a stepped cylinder jig to drill the holes in the Nikon/Pentax mount. This jig will be tightened in a wise and the holes drilled with a bench drill: accuracy of this process is very important.

Now the results:
- Very good sharpness (both lenses)
- Little bit of CA at f:2.8 but easy to remove in Photoshop (both lenses)
- Focusing to infinity is OK (both lenses)
- Aperture ring not easy to catch due to the Pentax body shape, littles fingers required. I am looking for a solution to make an aperture ring extension (both lenses)
- The weight: two bit pieces of aluminium and glass.....not a big deal with 35-70 but a tripod is required with 80-200.

If you have any question do not hesitate to contact me.

Best regards.

Bernard

Hello

I forgo to send pictures and drawings of my Nikon lenses modified to Pentax Mount.
Please apologize.

Best regards.

Bernard

Attached Images
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DMC-LX3  Photo 
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PENTAX K-7  Photo 
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PENTAX K-7  Photo 
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File Type: pdf NiktoPent1.pdf (252.9 KB, 176 views)
File Type: pdf NiktoPent2.pdf (271.9 KB, 184 views)
03-12-2013, 05:08 AM   #2
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Join Date: Jun 2011
Location: New York City
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Posts: 5,626
Whoah, nice work. Post any shots taken with it?
03-12-2013, 10:51 AM   #3
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Join Date: Feb 2013
Posts: 9
Original Poster
Thank very much

Pictures taken with 35-70 are coming soon.

Best regards
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