# Medium Format.

Started Jun 3, 2014 | Discussions thread
Re: Medium Format.

Russell Evans wrote:

fakuryu wrote:

Meuh wrote:

.
I worked out that the 55mm f2.8 on the 645z would be like a 28mm f1.4 on apcs, I have a 24mm f1.4 coming soon from samyang (that I won) but I don't think that on my k5 will give the same sort of look.

The 645D has a crop factor of .78x so the 55 f2.8 should be around 42mm f2.2? I'll try to post a shot I've taken with the 645D and the 55 f2.8 once I get home, it's not the best sample but something you might get some info on.

I see the 645z stated as being 1.7x larger than FF. Wouldn't the math be 55mm * 1/1.7 = 32.35mm for FF equivalence? That would then make 32.35mm * 1/1.5 = 21.56mm for APS-C equivalance? 1.7 * 1.5 is 2.55, so wouldn't that be 2 and a half stops in DOF, so f2.8 on MF would be f1.2 on APS-C or even a little larger?

Thank you
Russell

If we are talking into account whether using diagonal ratio or horizontal ratio when calculating the crop factor of FF to cropped 645

Using Diagonal the 645 is 55mm to 43.18 for FF so FF would have a crop factor of 1.27

Using horizontal 645 is 44mm wide and FF is 35.9mm wide having a crop factor of 1.22

What this means if use mainly shooting 3 by 2 you only gain a factor of 1.22 or a gain of 1.48 in surface area

With using 3/4 or 8/10 you have a crop factor of 1.27 or a gain of 1.61 in total surface area.

Yes F 2.8 on MF would be around F 1.15 on aps-c

If the 645Z uses the tech level in sensor development one would see that the 645z at iso 362 ( for diagonal) or iso 333 (for horizontal) would look like a FF at iso 225 and K5 at iso 100

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