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11-16-2019, 12:05 AM   #1
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Pentax K APS-C mirror clearance?

Hi all;

I just came into posession of a Soligor 35mm f3.5, preset, T-mount lens. I was thinking of doing some tilt-shift experiments with it on my KP or K-S2. By removing the T adaptor, it looks like I might be able to gain some registration distance into which I could fit a bellows bit for some T/S play. I know it's not going to be creating a very large image circle, so there won't be a lot of movement possible, but I'd still like to give it a go. The small rear element does protrude a bit; I was wondering, before I start sticking stuff onto or into my cameras, does anybody have an actual measurement of the mirror clearance behind the camera body mount on Pentax APS-C DSLRs? Would it be a greater distance than that of full frame K mount camera, because of the smaller sensor/mirror?

11-16-2019, 02:22 AM   #2
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The mechanics of having a smaller sensor (than full-frame 35mm) means that the mirror can be a couple of millimetres smaller as well, so clearances will be greater, but not by an enormous amount
It's for tests like this I keep an old totally mechanical body for messing about with

As an aside, on APS-C, a 35mm lens is unlikely to be very satisfactory for tilt-shift purposes, it's not really a "wide-angle" in this format. If you can find one, a 24mm Enna Lithagon in Praktina (not Praktica) mount shows more promise. The mount is removable, (though not necessarily interchangeable), and as the Praktina had a greater registration distance than M42 this lens gives just a little more "wriggle-room" ... though I doubt there'll be room enough for a set of bellows except for macro work ... a custom t/s mount might be possible if you have access to a lathe.



Afterthought :- Wider-angle T2-mount lenses are a bit thin on the ground, but a Tamron Adaptall or Vivitar TX 24mm lens, minus it's mount, could also give a starting point for something with a bit more "wriggle-room" if you can produce an adaptor to suit. Obviously, an even wider angle lens would probably be even better, but they still fetch good prices, so possibly not something to buy just for playing with

Good luck

Last edited by kypfer; 11-16-2019 at 02:43 AM. Reason: Afterthought
11-16-2019, 09:27 AM   #3
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The mirror will stay in the box. The apsc mirror more so than a ff mirror. You adaptor will also stay outside of the box... so, I see no problem besides making this thing work and realizing that tilt shift capabilities are very small and infinity focus will be a problem as well.
11-16-2019, 09:30 AM   #4
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Original Poster
QuoteOriginally posted by kypfer Quote
The mechanics of having a smaller sensor (than full-frame 35mm) means that the mirror can be a couple of millimetres smaller as well, so clearances will be greater, but not by an enormous amount
It's for tests like this I keep an old totally mechanical body for messing about with

As an aside, on APS-C, a 35mm lens is unlikely to be very satisfactory for tilt-shift purposes, it's not really a "wide-angle" in this format. If you can find one, a 24mm Enna Lithagon in Praktina (not Praktica) mount shows more promise. The mount is removable, (though not necessarily interchangeable), and as the Praktina had a greater registration distance than M42 this lens gives just a little more "wriggle-room" ... though I doubt there'll be room enough for a set of bellows except for macro work ... a custom t/s mount might be possible if you have access to a lathe.



Afterthought :- Wider-angle T2-mount lenses are a bit thin on the ground, but a Tamron Adaptall or Vivitar TX 24mm lens, minus it's mount, could also give a starting point for something with a bit more "wriggle-room" if you can produce an adaptor to suit. Obviously, an even wider angle lens would probably be even better, but they still fetch good prices, so possibly not something to buy just for playing with

Good luck
Thanks for the reply. I'll keep my eyes open for the wider alternatives you've suggested. I'd also thought of the taking lens from a Mamiya TLR for bigger image circle and longer registration distance, but TLR "wide" is a lot longer than APS-C DSLR "wide."

I've got the accordion bits from a couple of bellows that I would add some combination of mounts, adapter rings or narrow extension tubes for attaching the lens to the bellows and the whole assembly to the camera.


Last edited by Thagomizer; 11-16-2019 at 06:02 PM.
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