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09-25-2016, 06:22 PM   #1
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Pentax K lens to Pentax 645 mount adapter

Does an adapter that does this exist?

Pentax K lens to Pentax 645 mount adapter. I want to adapt my Rokinon 8mm fisheye to the 645Z. Offhand I'm thinking that it doesn't and wouldn't work but would like confirmation. The full frame K-1 can't capture the full circle of the fisheye image.

Thanks

09-25-2016, 06:46 PM   #2
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QuoteOriginally posted by PhilRich Quote
Does an adapter that does this exist?

Pentax K lens to Pentax 645 mount adapter. I want to adapt my Rokinon 8mm fisheye to the 645Z. Offhand I'm thinking that it doesn't and wouldn't work but would like confirmation. The full frame K-1 can't capture the full circle of the fisheye image.

Thanks
Nope, no adapters because the K-mount lens wouldn't fully cover the format.

Adam
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09-25-2016, 07:28 PM   #3
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I'm only want to capture the full circle projected by the lens, not fully cover the sensor. The sensor on the k-1 isn't big enough to capture the full circle projected by the lens.
09-25-2016, 08:55 PM   #4
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Isn't the 645 register distance substantially larger than the K mount's?

09-25-2016, 09:38 PM   #5
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QuoteOriginally posted by Cthulhugan Quote
Isn't the 645 register distance substantially larger than the K mount's?
Yes it is. So it won't be possible at infinity focus as is with a standard mount. However... If the lens is small enough to go inside the 645 mount you might be able to make a temporary mount the recessed into the 645. But you may need to watch out for the mirror. Does the 645 have a live view mode that keeps the mirror out of the way? Most of the Pentax bodies cycle the mirror when shooting in live view.
09-25-2016, 10:48 PM   #6
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Although your specific need does not depend on covering the sensor with the lens's image circle, the fact that it would not be covered (which most people would want) explains why such adaptors are not made.
09-26-2016, 01:47 AM   #7
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QuoteOriginally posted by Adam Quote
Nope, no adapters because the K-mount lens wouldn't fully cover the format.
Wouldn't an 8mm lens used with around 25mm of extension (approximate difference between the register distances of K-mount and 645) give an image circle approaching 3x the 'normal' diameter (subject to the focusing method employed within the lens). Whether 'infinity focus' will occur close to, or behind, the front element may preclude its practical application.

Bob
09-26-2016, 09:32 PM   #8
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Thanks for the replies. You have confirmed my thoughts that it would not work out. Here is a picture taken with the Rokinon 8mm lens on the K-1 that demonstrates the clipping that precludes getting a full circle shot. The camera was pointed straight up using the astrotracer feature. It sure would be nice to have the full circle. The picture almost shows the horizon as seen by the lens for a full 360 degrees.



09-26-2016, 10:21 PM - 1 Like   #9
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I am surprised that the Rokinon 8mm does not fully fit the 360 deg circle into an FF. The Sigma 8mm does. See this picture of mine:
http://www.astrobin.com/159762/

The flange back distance of 35mm lenses are much shorter than that of 645 lenses. So there is no convenient way (or entirely no way) to fit the lens to 645 and expect it to work. To adopt a 35mm lens to MF, you need to use a camera back rather than the full camera body. This is what I got after I fit a Canon 15mm fisheye to Mamiya 69 film back:
http://www.astrobin.com/77503/
I suppose you can do the same to an MF digital back, but I believe you will go through lots of troubles that are probably not worthwhile. Just getting a Sigma is much easier.

Alternatively, you can take a picture with your Rokinon 8mm, rotate the camera/lens by 90 deg, and take another picture. You should be able to get a full circe after blending them together.

Cheers,
Wei-Hao
09-28-2016, 12:18 PM   #10
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Good, the Sigma 8mm is the solution. BTW, those are really nice sky shots!

Thanks
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