# EF300 f2.8 USM IS vs EF100-400 USM IS

Started Feb 8, 2009 | Discussions thread
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 Re: It's 1.6^2 In reply to number95, Feb 12, 2009

Hi number 95
Thanks for calculation. You are right. Thats exactly what i wrote

640 mm - 10% = 576 mm

Just to clarify my thoughts follow explanation:

Canon Eos 5D MKII
5616 px (length) x 3714 px (width) = 20'587'824 px = almost 21 Mpix

Canon Eos 40D
3888 px (length) x 2592 px (width) = 10'077'696 px = about 10 Mpix

20587824 / 10077696 = 2.0697016. The root of it = 1.4386457

That means: To print with the same resolution on paper you can crop a 5dMK II

by factor 1.44 and you reach same quality because you than have exactly the same size in pixel as a 40D.

The crop factor of the aps-sensor is 1.6 as we all know (for 40D)
The crop factor by the real pixel in Original size is 1.44 (for 5DMKII)

That means the difference is 1.6 - 1.44 = 0.16 (exactly 10%) wich has the 40D in advantage.

Oh how surprising: 640mm -10 % = 576 mm...

Best regards

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