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07-15-2014, 02:58 PM   #1
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Nikon 300mm f/2.8 on Pentax 6x7

Hi,

Has anyone else heard of this or had one (or long 35mm telephoto) converted to 6x7 or 645 mount? It mentions that this lens is supposed to cover 6x9.

https://www.flickr.com/photos/43168849@N08/4724070657/

Thanks,

Yuri

PS No need to tell me this might be expensive, or impractical, or why would I want to do this... just curious about other people's experience.

07-15-2014, 03:48 PM   #2
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Nope. But pretty amazing the image circle is large enough. I'd never have guessed.
07-15-2014, 03:49 PM   #3
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yes, i converted a canon FD mount 600mm telephoto to pentax 645 and shoot it on my 645D. We have used the telephoto stills lenses for years to shoot 65mm film negative, many of them cover at least 55mm image circle.
07-15-2014, 04:57 PM   #4
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I've got an SMCT 500/4.5 that has been modified for 6x7. It is allegedly a factory modification that was offered by Pentax. A lot of longer lens designs have a much greater image circle than the format of the lens, but in many cases the edges will be a lot less sharp than the centre. Nowadays the Petzval lens is sought after for its strange bokeh, but back in the 19th century that was never apparent because only the central part of the image circle was used and that part was very sharp.

FWIW the mods to the 500/4.5 consisted of removing a baffle near the rear of the lens and changing the mount tube. For a 35mm camera the baffle would prevent extraneous light affecting the exposure, while for a 6x7 that light is no longer extraneous

07-22-2014, 04:45 PM   #5
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Thank you all for the replies. Need to do some more research on which telephoto lenses are suitable for this.
07-22-2014, 05:34 PM   #6
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QuoteOriginally posted by tuco Quote
amazing the image circle is large enough. I'd never have guessed.
The image circle on telephoto lenses can really surprise you. I have seen the Leica 400mm f/2.8 APO-Telyt-R used on a Leica S2 - the results were impressively good even at f/2.8
07-23-2014, 06:27 AM   #7
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Any chance of getting some details on how this was done? Perhaps a photo as well?

QuoteOriginally posted by 672 Quote
yes, i converted a canon FD mount 600mm telephoto to pentax 645 and shoot it on my 645D. We have used the telephoto stills lenses for years to shoot 65mm film negative, many of them cover at least 55mm image circle.
07-23-2014, 08:29 AM   #8
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I am actually liking the concept of a 300/2.8 adapted to the 645Z. Back in 2010 when this was done for the 67, it cost $1000 Hong Kong dollars. Might be a bit more now. Almost worth going to Hong Kong, finding a lens and converting - whether it be AIS of FD or something else of quality.

---------- Post added 07-23-2014 at 09:37 AM ----------

you know, I have a Sigma 120-300/f2.8 in a Nikon mount, first version, sitting around. I occasionally think about selling it but forget. But now, I'm wondering if it could be converted to the P645 mount - it would only have to cover the digital sensor not full-frame as far as I'm concerned. With the first version, it still has the aperture ring on the lens. hmmmm. I haven't seen focus -peaking on the 645Z yet, is it there?

07-23-2014, 08:48 AM   #9
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I picked up one of these - Sigma (Nikon) 120-300mm f/2.8 (non DG, non OS) recently... hmmm having that on my 645N (so, I'd like full frame coverage) would be quite nice. Have you looked into converting into a 645 mount? I wonder is we found a shop to do this, would they give us a break on getting two converted...

QuoteOriginally posted by hsteeves Quote
I am actually liking the concept of a 300/2.8 adapted to the 645Z. Back in 2010 when this was done for the 67, it cost $1000 Hong Kong dollars. Might be a bit more now. Almost worth going to Hong Kong, finding a lens and converting - whether it be AIS of FD or something else of quality.

---------- Post added 07-23-2014 at 09:37 AM ----------

you know, I have a Sigma 120-300/f2.8 in a Nikon mount, first version, sitting around. I occasionally think about selling it but forget. But now, I'm wondering if it could be converted to the P645 mount - it would only have to cover the digital sensor not full-frame as far as I'm concerned. With the first version, it still has the aperture ring on the lens. hmmmm. I haven't seen focus -peaking on the 645Z yet, is it there?
07-23-2014, 11:02 AM   #10
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QuoteOriginally posted by yurihuta Quote
I picked up one of these - Sigma (Nikon) 120-300mm f/2.8 (non DG, non OS) recently... hmmm having that on my 645N (so, I'd like full frame coverage) would be quite nice. Have you looked into converting into a 645 mount? I wonder is we found a shop to do this, would they give us a break on getting two converted...
yurihuta: its not going to work. I figured with the difference in registration distances between Nikon and P645, we would need about 40mm of bare tube in the back of the lens that could be cut out. I just looked at mine and there is a glass element about 15-20mm in back there. Oh well, cheap 300/2.8 here I come. I have an old Tamron 300SP but I don't know about its sharpness.

Last edited by hsteeves; 07-23-2014 at 11:03 AM. Reason: addition.
07-23-2014, 10:36 PM   #11
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QuoteOriginally posted by yurihuta Quote
Any chance of getting some details on how this was done? Perhaps a photo as well?
yes, i will take a photo of it when i get home from my travels. there are a couple of photos shot with this set up in the "post your medium format photos" section of this forum. i think you could search for all my post in there. i usually list the lens used.

as someone else here mentioned you need a lot of room to shorten the back end of the lens to make a 35mm format lens work in this manner. in the case of the canon FD 600mm the rear element is way way inside the barrel. after shortening the back of the lens, i used a #2 pentax 645 macro tube for the lens mount , after stripping the tube of the front end and everything that is inside of it , you are left with an empty tube and lens mount . fairly easy to attach to lens.
07-24-2014, 07:12 AM   #12
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QuoteOriginally posted by 672 Quote
yes, i will take a photo of it when i get home from my travels. there are a couple of photos shot with this set up in the "post your medium format photos" section of this forum. i think you could search for all my post in there. i usually list the lens used.

as someone else here mentioned you need a lot of room to shorten the back end of the lens to make a 35mm format lens work in this manner. in the case of the canon FD 600mm the rear element is way way inside the barrel. after shortening the back of the lens, i used a #2 pentax 645 macro tube for the lens mount , after stripping the tube of the front end and everything that is inside of it , you are left with an empty tube and lens mount . fairly easy to attach to lens.
672: how are adjusting the aperture on your modified lens or was the aperture ring up the lens instead of being by the lens mount?
07-24-2014, 04:57 PM   #13
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QuoteOriginally posted by hsteeves Quote
yurihuta: its not going to work. I figured with the difference in registration distances between Nikon and P645, we would need about 40mm of bare tube in the back of the lens that could be cut out. I just looked at mine and there is a glass element about 15-20mm in back there. Oh well, cheap 300/2.8 here I come. I have an old Tamron 300SP but I don't know about its sharpness.
It shouldn't be that bad, the P645 register is 70.87mm while the Nikon F is 46.5 so that's less than 25mm difference. Still not close enough for the lens you are looking at but better than 40mm.
07-24-2014, 06:50 PM   #14
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QuoteOriginally posted by hsteeves Quote
672: how are adjusting the aperture on your modified lens or was the aperture ring up the lens instead of being by the lens mount?
My mods to 645D mount were not the first mods this particular copy ever received. Initially it was modified for cinematography and has a manual , no clicks, iris adjustment. Then it was set to EOS mount for a while and lately its got this 645 mount on it. I will look for a picture to post or take one when i get home.
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