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06-11-2011, 02:25 PM   #1
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Pentax 67 to 645 conversion chart

Hi
Does anyone know of a chart showing how 6/7 lenses translate on 645D cameras. Or could someone help me do the math by giving the factor needed to compute the equivalent.

Thanks

06-11-2011, 03:12 PM   #2
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Why not simply work in angular magnification. Just divide the focal length by the sensor diagonal. You can use that magnification factor to convert the 67 focal length to 645 equivalent. Personally, I find the angular magnification without a focal length conversion easier.

Last edited by Yamanobori; 06-11-2011 at 03:33 PM.
06-11-2011, 03:57 PM   #3
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HUH?

Ok that's see if I understand. The diagonal of the 6x7 is 92.19544mm I think. If I want to figure the equivalent I start by dividing the focal length of the lens say 75mm by 92.19544. That would be .813. Now what do I do?

How about this: The diagonal of the 645D sensor is 55MM so the "normal" lens is 55mm. The diagonal of the 67 is 92mm roughly 2x, then 67 lens are about twice that of the 645D lenses. Is that right?

Last edited by elsdad; 06-11-2011 at 04:10 PM.
06-11-2011, 04:11 PM   #4
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Not quite. You want to used the 75mm on the 645D. Divide 75mm by 55mm (the diagonal of the 645D sensor). That has an angular magnification of 1.36X.

In 67 terms, that is like 92mm (the 67 diagonal) X 1.36 or 125mm lens.

BTW, 1X is a normal lens. So a 67 55mm lens is normal--like a 90mm on a 67.

BTW, The 67 to 645 crop factor is about 1.7 (1.67)--92mm divided by 55mm.

It is simply geometric relationships between the image diagonals and the focal lengths.

06-11-2011, 04:27 PM   #5
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So the 75mm will be like 92mm
06-11-2011, 05:57 PM   #6
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The 75mm on the 645D will be like a 125mm on a 67.
06-12-2011, 04:32 AM   #7
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Thanks
So

125mm on a 67 = 75mm on 645D = 59mm on 35mm FF

Last edited by elsdad; 06-12-2011 at 04:42 AM.
06-12-2011, 08:28 AM   #8
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You got it, my friend.

06-12-2011, 02:33 PM   #9
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Thanks!!!!!
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