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02-17-2011, 12:42 AM   #1
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Crop factor of the 645d

What is the crop factor of the 645d vs full frame

And more specifically what focal length is the 55mm from the 645d on my K-5?

I'm hiring a 645d and 55mm for a day and i wanted to know how its going to 'look' to me, someone who is used to a 1.5x crop factor.

02-17-2011, 12:58 AM   #2
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The focal lengt of the 55mm in 645D is 75mm in film-645, 43mm on a FullFrame camera like D700 and 28mm in K-5.
02-17-2011, 02:33 AM   #3
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Very helpful Ron - I was wondering about this recently.
02-17-2011, 03:14 AM   #4
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What about the 67 lenses with adapter? My 100mm Macro (which looks like a 50mm on a D700) now seems like a 70-75mm on the 645D. The 45mm turns out to be a 35mm. Not that I would not have expected this but is there any factor a P645D user can work with?

02-17-2011, 03:16 AM   #5
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QuoteOriginally posted by DSims Quote
Very helpful Ron - I was wondering about this recently.
Image ratio between 645D/645Film on one side and FF/APSC on the other are different so "crop factors" have to be taken with a pinch of salt.

Depending on own your like your images (square, 4/3, 2/3) your focal equivalence will be different.

Just sayin'.
02-17-2011, 04:28 AM   #6
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QuoteOriginally posted by phonoline Quote
t is there any factor a P645D user can work with
to get the 35mm equivalent for a lens on full frame 645 multiply it's focal length by 0.6X for the 645D multiply the focal length by 0.78X

the sensor in the 645D is 1.7 times larger than 35mm film, so bear in mind for a set magnification you need to get 1.7 times closer to your subject with the 645D than you would have to with 35mm so consider that in your DOF calculations as well.
02-17-2011, 10:46 AM   #7
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I only print 4:5 (8x10, 11x14, 16x20, 20x25, 24x30, ...) so to me it is the short side which matters.

This way, the full-frame 35mm equivalent focus length is derived with a factor of 24/33=1/1.375=0.727, and the 55mm acts exactly as a 40mm lens on my D700, after I crop the both to 4:5.

My backbone landscape camera is a Pentax 67, for which after many years I know the "seeing" of each of their lenses. Now, I need apply (multiply) a factor of 56/33=1.7 to get the terms of 67 lens, so the 55mm gives me the field of view of 93mm lens on my 6x7 film, about the long end of my 55-100mm zoom.

For Pentax 645 the factor is 42.5/33=1.29.
02-17-2011, 02:47 PM   #8
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http://i.pbase.com/o2/50/276250/1/124042570.Vepq7MDW.PENTAX645EQ10.jpg


PENTAX645EQ10.jpg photo - Ramón Torres photos at pbase.com

Ramón

02-20-2011, 11:19 AM   #9
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QuoteOriginally posted by WerTicus Quote
1. What is the crop factor of the 645d vs full frame
2. And more specifically what focal length is the 55mm from the 645d on my K-5?
1. Crop is nearly 1.27
If you want to know, what is 55/2,8 on 645D in terms of 35 mm film, you must divide
55/1.27 = 43 mm in equivalent. Like 43 Limited on 35 mm film.
2. Crop is nearly 1.52
If you want to know, what is 55/2,8 on K-5 in terms of 35 mm film, you must multiply 55x1.52 = 84 mm in equivalent. Like 85mm "stars" on 35 mm film.
06-12-2011, 08:35 PM   #10
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I would like to be certain of what the various crop factors mean on a specific 645 lens.

Suppose one uses a SMC Pentax FA 645 zoom 150-300 f/5.6 at full length (300mm) on a 645D. Will this lens be functioning in terms of magnification like a longer lens (>300mm) or like a shorter lens (<300mm)?
06-12-2011, 08:44 PM   #11
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the 645 100-300mm f/5.6 behaves like a 78~234mm lens in 35mm terms, so it will be performing as a longer lens relative to full frame 645.
06-12-2011, 11:01 PM   #12
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https://www.pentaxforums.com/forums/general-photography/55197-camera-lens-math-easy.html
06-13-2011, 08:37 AM   #13
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So the Pentax 645 150-300mm lens on my 645D will only give me magnification equivalent to a 234mm lens on my Canon 5D2. Is that correct?
06-13-2011, 09:41 AM   #14
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QuoteOriginally posted by mstratil Quote
So the Pentax 645 150-300mm lens on my 645D will only give me magnification equivalent to a 234mm lens on my Canon 5D2. Is that correct?
Only? That's a lot! We with 6x7 MF film cameras would have to drag around a monster lens to get 234mm equivalent in 135 format.
06-13-2011, 05:28 PM   #15
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QuoteOriginally posted by mstratil Quote
So the Pentax 645 150-300mm lens on my 645D will only give me magnification equivalent to a 234mm lens on my Canon 5D2. Is that correct?
no on a 24X36mm sensor the Pentax 150-300mm f/5.6 @ 300mm it will behave like a 300mm lens, a slow 300mm lens.
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