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03-28-2017, 04:26 PM   #1
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Can I use older 645 A manual lens on a K1?

In preparation of picking up a K-1 in the next couple of weeks, I've started scouring Craigslist and other places for older Pentax lenses. I came across this one Pentax a 645 zoom 80-160mm 4.5 for $150.00 and was wondering if it would work on the K1.Do the 645 and ht eK1 share a K style mount, or is teh 645 a different mount entirely?

03-28-2017, 04:28 PM   #2
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Different mount
03-28-2017, 04:31 PM   #3
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QuoteOriginally posted by BullsOnParade81 Quote
Different mount
Damn... thanks
03-28-2017, 04:38 PM   #4
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QuoteOriginally posted by Craigbob Quote
Damn... thanks
There are adapters though

03-28-2017, 05:03 PM   #5
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FYI -- a 645 80-160mm lens with an adapter on a K1 (35mm) would be equivalent FOV to a 50-100mm lens. A REALLY good lens in that price range needing no adapter would be the Pentax-A 35-105mm. It's FF and referred to as the "Stack of Primes". And it's faster at a constant f/3.5.

https://www.pentaxforums.com/lensreviews/SMC-Pentax-A-35-105mm-F3.5-Zoom-Lens.html

Last edited by ripper2860; 03-28-2017 at 05:08 PM.
03-28-2017, 05:37 PM   #6
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as others said, they make an adapter, but that is not a particularly fast lens and is very bulky. It may not even look very good on FF.

BTW a 645 80-160 is still 80-160 on FF. The equivalent focal length only changes if you are talking about using the same lens on both cameras.
03-28-2017, 05:43 PM   #7
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QuoteOriginally posted by mikeSF Quote

BTW a 645 80-160 is still 80-160 on FF. The equivalent focal length only changes if you are talking about using the same lens on both cameras.
Focal length never changes, but wouldn't the effective Field of View (FOV) change given that the 645 has a crop factor of .62075x vs the 35mm crop factor of 1x? Sure if you put a 645 80-160mm on a Pentax Q (don't know if it's even possible or if one would want to) it's still 80-160mm FL, but the image FOV rendered is quite different compared to the same lens on a 645 or even a 35mm film/sensor.


Last edited by ripper2860; 03-28-2017 at 05:48 PM.
03-28-2017, 05:48 PM   #8
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QuoteOriginally posted by ripper2860 Quote
Focal length never changes, but wouldn't the effective Field of View (FOV) change given that 645 has a crop factor of .62075x vs the 35mm crop factor of 1x?
No. It would be an 80-160mm lens on a K-1. It's called 35mm equivalent because you are comparing a non-35mm format to a 35mm format...

You would need a 50-100mm lens on a K-1 to have the same FOV as the 80-160 on a 645...

Last edited by boriscleto; 03-28-2017 at 05:58 PM.
03-28-2017, 05:50 PM   #9
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Of course the FOV will change, but it will look a 80-160mm lens on the K-1.

QuoteOriginally posted by ripper2860 Quote
A FYI -- a 645 80-160mm lens with an adapter on a K1 (35mm) would be equivalent FOV to a 50-100mm lens.
The 80-160s on a 645 would look like a ~45-90 on a FullFrame sensor, if my maths is not off (and it might be!)

Last edited by Topsy; 03-28-2017 at 06:01 PM.
03-28-2017, 06:00 PM - 2 Likes   #10
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Doh! Light-bulb just went off!! I stand corrected.

OP -- forget everything I posted except this post. Except the fact that a A35-105 is a great lens, that is. :-/

(Feeling pretty dumb right about now)

Thanks.

Last edited by ripper2860; 03-28-2017 at 06:19 PM.
03-29-2017, 04:11 AM   #11
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QuoteOriginally posted by boriscleto Quote
No. It would be an 80-160mm lens on a K-1. It's called 35mm equivalent because you are comparing a non-35mm format to a 35mm format...

You would need a 50-100mm lens on a K-1 to have the same FOV as the 80-160 on a 645...
NO, NO. A 80-160 645 lens with the 645xK adapter will still have the same FOV in 35mm as is in 645. Try to find the 645 x K adapter manual and read carefully!! I have several 645 lenses and they have the very same FOV in the 35mm format as the K lenses counterpart.

That would be true IF you mount a 645 directly on a K body. As that is impossible and an adapter is needed for that what makes the 645 lens to behave the same as the K lens in terms of FOV.
03-29-2017, 04:26 AM   #12
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Unless the adapter has corrective glass in it I can't see how the FOV on an image taken could possibly stay the same. And there's no reason to add corrective glass or a 'lens turbo' to it either as the flange distance is larger on the 645.

Assuming you would be able to mount it directly to k-mount you'd simply not be able to focus as it would constantly be focused way past infinity.
03-29-2017, 05:47 AM   #13
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QuoteOriginally posted by Topsy Quote
Unless the adapter has corrective glass in it I can't see how the FOV on an image taken could possibly stay the same. And there's no reason to add corrective glass or a 'lens turbo' to it either as the flange distance is larger on the 645.

Assuming you would be able to mount it directly to k-mount you'd simply not be able to focus as it would constantly be focused way past infinity.

The fov will be different.
But the fov of the 80mm end will be exactly the same when mounted on a k-1 as it would be from the DFA 70-210 full frame set to 80mm on the same k-1.

The fov of the 645 lens on a 645z will be wider. On a 645n (true 645) it will be wider still.
03-29-2017, 06:04 AM - 1 Like   #14
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QuoteOriginally posted by RuiC Quote
Try to find the 645 x K adapter manual and read carefully!! I have several 645 lenses and they have the very same FOV in the 35mm format as the K lenses counterpart.
QuoteQuote:
The angle of view of 645 lens becomes smaller when the lens is mounted onto the 35mm camera, just the same as the 35mm camera lens with the same focal length.
Which is exactly what I said above. If you want the same FoV on a 35mm camera as you get when using the lens on a 645 camera you have to use a smaller focal length on the 35mm camera.

The 80-160mm, on 645 film, has a FoV of 39-20º. To get the same FoV on 35mm FF you need a 50-100mm lens...but the 645 80-160mm when used on 35mm FF would have a FoV of 30-15º, the same would be true of an 80-160mm lens designed for 35mm...
03-29-2017, 06:18 AM   #15
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QuoteOriginally posted by boriscleto Quote
Which is exactly what I said above. If you want the same FoV on a 35mm camera as you get when using the lens on a 645 camera you have to use a smaller focal length on the 35mm camera.

The 80-160mm, on 645 film, has a FoV of 39-20º. To get the same FoV on 35mm FF you need a 50-100mm lens...but the 645 80-160mm when used on 35mm FF would have a FoV of 30-15º, the same would be true of an 80-160mm lens designed for 35mm...
Mount a 645 120mm + adapter on a K body and then mount a SMC K 120mm on the same K body and compare!! That´s all you need!
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