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11-30-2017, 03:51 AM   #1
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Lens question

Guys, Can I use non 6x7 lenses on 645D? For example some cine and projection lenses which cover medium format size. Or only pentax 645 and pentax 67 lenses?
I have wide amount of projection lenses like 100 1.4, 100 1.5, I wonder if it's possible to focus at 1.4?

11-30-2017, 06:42 AM   #2
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It's a matter of: 1) can you find or make an adapter that will fit the lens onto your 645; 2) is there enough back focus (distance from the rear of the lens to plane of focus) to permit focusing @ infinity. I think the back focus will be a major problem. Cine lenses generally can be mounted on MFT* but not on APS-C. So I'm doubtful they can be mounted on a 645. Projection lenses, however, are different, and too variable to predict what is or is not possible, although mounting one**, I suspect, will be the major obstacle.

*Commercial adapters exist to mount cine lenses on MFT

**I've never seen an adapter to mount a projection lens onto any still camera of any format. Jean Poitier who posts on PF has successfully attached projection lenses onto Pentax bodies using ingenuity and tape (sometimes). SFAIK projection lenses essentially never have a rear thread or bayonet, obviously a major barrier/problem. Bronica used to make a bellows that had a rear mount for the camera body, and a lens board at the front that could be custom drilled to attach a variety of lenses, especially press/view camera lenses that were designed to mount on such a board. But how a projection lens with no jam-nut system might be attached I have no idea.

Last edited by WPRESTO; 11-30-2017 at 06:51 AM.
11-30-2017, 07:34 AM   #3
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I use custom-made helicoid adapter on my Sony for any projection lens I have (around 20 in total). There is pentax 645 to m65 helicoid-adapter available so it's not a problem to adapt any projection lens.
Mostly it's very fast lens, 90 1.25, 100 1.4, 141 1.9. So I wonder if it's possible to shoot with non-generic lens. I have 2 ways now: wait for new Sony a7iii or get used 645D without live view.

Also I want to ask about flange focal distance. For Sony most of my fast projection lenses have infinity working from around 30-40mm. That means I will not receive infinity or full body portrait on 645D using most of my projection lenses?
11-30-2017, 02:12 PM   #4
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here are formulae to determine focal distance for a lens, but they aren't that easy to use (some parameters in the equation may be difficult to determine for a particular lens). You probably should just experiment. In a dark room, illuminate one wall, hold the lens as close against the lens opening of the camera as possible, move back and forth until the illuminated wall is in focus to get at least an approximation of the FOV and maximum focal distance. That should tell you whether it's worth the effort to devise a way to mount the lens on your 645. Or go outside, hold the lens as close as possible against the front of the camera, and point at objects at different distances until you find one that is in focus. Just pan down toward your feet to see when the ground comes into focus. That should give you a rough idea, again enough to see if it is worth trying to mount the lens for your intended usage.

12-01-2017, 01:11 AM   #5
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I have several fast projector lenses (doublets and triplets) that I've adapted to use on my Canon 35mm bodies but their rear focus distance is between 52mm and 58mm......much too short to use on 645 bodies.

Bob
12-07-2017, 08:34 AM   #6
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QuoteOriginally posted by durell Quote
Guys, Can I use non 6x7 lenses on 645D? For example some cine and projection lenses which cover medium format size. Or only pentax 645 and pentax 67 lenses?
I have wide amount of projection lenses like 100 1.4, 100 1.5, I wonder if it's possible to focus at 1.4?
Hi,

In case you are curious, there is this thread about projection lenses here : https://www.pentaxforums.com/forums/122-lens-clubs/264161-projector-lens-club-23.html

I have never really thought about using one on my film Pentax 645, but it could be interesting. The registration distance(s) might be difficult to get around. I have a couple of odd "large(r) format" lenses lying about which might be "doable" as well ...

Please let us know if you find out anything good or bad. Thanks in advance and cheers, J
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