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10-14-2014, 11:20 AM   #1
Leonski
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Equivalent lens Mamiya - Pentax K-5

Pls, eqvivalent lens Mamiya M645, lens Mamiya Sekor C f2,8 55mm on Pentax K-5, APSC.
All the best from Leonski, Macedonia

10-14-2014, 11:22 AM   #2
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A 55mm lens on 645 is equivalent to a 35mm lens on 35mm FF. So you would need a 24mm lens on APS-C.
10-14-2014, 11:38 AM   #3
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QuoteOriginally posted by Leonski Quote
Pls, eqvivalent lens Mamiya M645, lens Mamiya Sekor C f2,8 55mm on Pentax K-5, APSC.
All the best from Leonski, Macedonia
is that 645 a film camera?
10-14-2014, 01:34 PM   #4
Leonski
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Mamiya M645 1000S film camera

Yes, Mamiya M645 1000S film camera.

10-14-2014, 02:23 PM   #5
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645 = 56x41 = 69.4mm diagonal
APS-C = 28.4mm diagonal

55mm*(28.4/69.4) = 22.5mm
f/2.8*(28.4/69.4) = 1.145

So a 23mm F/1.1 would have roughly the same field of view (on the diagonal) with the same light-gathering ability.
10-14-2014, 02:51 PM   #6
Leonski
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Thanks

Thank You.
10-14-2014, 03:02 PM   #7
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F/2.8 is F/2.8. A 24mm F/2.8 lens would give you the equivalent FoV and the same exposure. DoF and perspective are a different matter.
10-14-2014, 03:14 PM   #8
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QuoteOriginally posted by boriscleto Quote
DoF and perspective are a different matter.
Yes, but still potentially relevant to the OP's question.

10-14-2014, 03:19 PM   #9
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QuoteOriginally posted by boriscleto Quote
F/2.8 is F/2.8.
Yup.

And and F/2.8 gathers the same amount of light as an F/1.1, when you change formats.

FYI perspective is the same on the 23mm APS-C and the 55mm 645, despite whatever you've seen on the interwebz.
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