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03-09-2008, 10:40 PM   #1
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Mounting a Topcon RE lenses on Pentax K

I guess this is one of the 'what I did during a rainy day' posts:

I recently got a Topcor 1:2.8 f=3.5cm and a Topcor 1:3.5 f=135mm. I replaced the bayonet of the Topcon lenses with the one of two old Pentax K lenses. The whole story with samples is here: Converting Topcon lenses to Pentax K

Here are the results:



A sample from the 35mm/2.8:


and from the 135mm/3.5 (50% crop):


- enjoy

03-10-2008, 06:46 AM   #2
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Not bad for the price of a few chocolate bars
03-10-2008, 08:53 AM   #3
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Good stuff...and a very well-detailed explanation of the process. Thanks...
03-10-2008, 08:53 AM   #4
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CHSE,
Nice work. I added a pentax mount to my Olympus/Cosina 28-70 F2.8 zoom. It works great and now I need to add a diaphiam coupling arm and light baffle. The registration distance is 46mm on the OM lenses which is greater then the 45.6mm of the Pentax. I used a the M42 adapter which has a 0.6mm flange. This added just the right amount of spacing. Here is a list of the various distances of SLR's. As you can see the Nikon is a good canadate at 46.5mm.

Registration Distance
(data from internet sources)

Pentax 45.5mm (K mount and M42 screw)

Nikon 46.5mm

Olympus OM 46.0mm

Evolt 38.5mm

Minolta 44.0mm ( actual measurement by me)

Canon FD 42.0mm

Canon EF 44.0mm

Leica R 47.0mm

Konica ?mm

Topcon 44.7mm

Dave


Last edited by Big Dave; 08-10-2008 at 03:44 PM.
03-10-2008, 07:49 PM   #5
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QuoteOriginally posted by Big Dave Quote
CHSE,
Nice work. I added a pentax mount to my Olympus/Cosina 28-70 F2.8 zoom. It works great and now I need to add a diaphiam coupling arm and light baffle. The registration distance is 46mm on the OM lenses which is greater then the 45.6mm of the Pentax. I used a the M42 adapter which has a 0.6mm flange. Here is a list of the various distances of SLR's. As you can see the Nikon is a good canadate at 46.5mm.
Dave
Thanks- the olympus looks nice, too, the new AF lenses just don't have the same feeling. Here is something I am wondering about for a while: Nearly all Pentax bayonets are the same when removed from the lens, this might also be true for many other lens manufacturers, since they only wanted to design it once. I would also assume that the only difference between the non-OEM lenses is the bayonet, so maybe if you get a cheap Cosina Pentax lens you can completely convert the Olympus to Pentax with it.

QuoteOriginally posted by Big Dave Quote
Here is a list of the various distances of SLR's. As you can see the Nikon is a good canadate at 46.5mm.
Dave
You can actually mount the old Nikon non-AI lenses directly on Pentax, they do not lock in but stay on the camera- these are beautifully made as well.
03-10-2008, 07:53 PM   #6
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More Hacks are here:

I just started another blog with hacks, modifications and useful links here:

Pentax Hacks
04-10-2008, 03:26 AM   #7
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old Nikon non-AI lenses on Pentax

QuoteOriginally posted by chse Quote
You can actually mount the old Nikon non-AI lenses directly on Pentax, they do not lock in but stay on the camera- these are beautifully made as well.
Just followed your suggestion, but one (50mm f1.4) focused right even slightly past infinite, whereas my 100mm f2.5 could not - can't understand why.
I could barely screw both of them in a very very minimal fraction of their twist run, though - was that what you meant with "stay on the camera"? Yes then they do stay, but just barely. I wouldn't dare let hold of the lens, lest it may drop to the floor ... Am I being over anxious, or simply was I too hesitant to force the twist a little further lest the bayonet (male or female) might be damaged?
Thanks
04-10-2008, 06:51 AM   #8
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QuoteOriginally posted by goofi Quote
Just followed your suggestion, but one (50mm f1.4) focused right even slightly past infinite, whereas my 100mm f2.5 could not - can't understand why.
I could barely screw both of them in a very very minimal fraction of their twist run, though - was that what you meant with "stay on the camera"? Yes then they do stay, but just barely. I wouldn't dare let hold of the lens, lest it may drop to the floor ... Am I being over anxious, or simply was I too hesitant to force the twist a little further lest the bayonet (male or female) might be damaged?
Thanks
some Nikon lenses fit better than others. there's a discussion on DPReview about it from a long time back

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