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Converting an M42 300mm F4 Meyer-Optik to Pentax K
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PostPosted: Fri Feb 27, 2009 4:24 am    Post subject: Converting an M42 300mm F4 Meyer-Optik to Pentax K Reply with quote
I wanted to use my Pentacon (Meyer Optik) Orestegor 300mm f4 with my Pentax K200D, I found the best option to keep the lens easy-to-use would be to permanently convert the lens for K-mount use. Since this lens weighs around 5 pounds (!) I knew it'd need to securely lock onto the lens. So, I purchased the "macro" variety of M42 to K-mount adapters that include the locking flange. I took the rear "cone" of the lens to a machinist and had him machine off the different in thickness from the flange, as well as cut a new guide slot so the lens sits with the scale facing up on the camera. A small amount of non-precision grinding was also required on the rear portion of the lens that enters the cone.
Here's the before and after pictures of the conversion:

Adapter on the cone:


"Face" of the cone to be machined down:


Ground rear lens projection, and the newly-machined cone:


Fits like a glove!


Next on the to-do list: finish the remote release cable for the camera gunstock!


PostPosted: Fri Feb 27, 2009 11:03 am    Post subject: Reply with quote
I did a similar thing but I just used loctite to fasten a M42-K mount adapter to the Meyer M42 cone. Nice work you did.


PostPosted: Mon Mar 23, 2009 3:22 am    Post subject: Reply with quote
Hi everyone! Good weather has come, and here's some links to pictures I got out of the Meyer:

http://www.flickr.com/photos/comp_wiz101/3373550143/sizes/l/
http://www.flickr.com/photos/comp_wiz101/3374352092/sizes/l/
http://www.flickr.com/photos/comp_wiz101/3373555541/sizes/l/

Most of these were shot around F5.6 to F8


PostPosted: Fri Apr 17, 2009 10:13 pm    Post subject: Reply with quote
Very nice. I always like to see people think out of the box when working out a solution to a lens mount problem.

The images prove that the method works well.


PostPosted: Fri Apr 17, 2009 10:44 pm    Post subject: Reply with quote
Big Dawg wrote:
I did a similar thing but I just used loctite to fasten a M42-K mount adapter to the Meyer M42 cone. Nice work you did.


Careful with glued adapter I did also long time ago and after a couple of good usage my lens felt down even if lens wasn't heavy at all.


PostPosted: Fri Apr 17, 2009 10:46 pm    Post subject: Reply with quote
Why you didn't use M42 Pentax adapter instead of made this conversion ?


PostPosted: Sat Apr 18, 2009 12:09 am    Post subject: Reply with quote
Attila wrote:
Why you didn't use M42 Pentax adapter instead of made this conversion ?


The thin metal used to hold the pentax-built adapter in place wasn't robust enough to trust out in the field. I usually mount this lens to a gunstock and the camera is supported by the mount (and by my camera strap should the worst happen)
Also, this conversion does two other things I need:
a) permanent bayonet mount makes it quick to change the lens in the field
b) The wide flange on the adapter I chose shorts out the lens information contacts, which for some odd reason makes aperture priority mode work properly.
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