Why F/6.3, when the same lens (via adapter) is F/5.6 on DSLR?

Started Jun 19, 2014 | Discussions thread
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007peter
007peter Forum Pro • Posts: 10,431
Why F/6.3, when the same lens (via adapter) is F/5.6 on DSLR?

DSLR:

  • Canon 55-250mm IS STM F/4 ~ F/5.6

Yet the same lens for Mirrorless M is

  • Canon 55-250mm IS STM F/4.5 ~ F/6.3

its the same with Sony: its 55-250mm lens for Alpha dslr = 5.6, but mirrorless NEX = 6.3.  Is there something about mirrorless that rub 1/3 stop of light???

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Canon EOS 550D Panasonic Lumix DMC-GF6 Canon EF-S 18-55mm f/3.5-5.6 IS II Panasonic Leica DG Summilux 15mm F1.7 ASPH Panasonic Lumix G 25mm F1.7 ASPH
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