syder said:ecka said:I bought the Sigma 50/1.4 instead, it was very nice, pretty sharp at 1.4 even on a crop body.
On a crop body you use the sweet spot of a FF lens, so it's far more likely to be sharp at the borders... The sigma 50/f1.4 is known as sharp in the centre and soft at the border...
http://www.photozone.de/canon-eos/522-sigma50f14eosff?start=1
You are right about the sweet spot. However, there is a big difference in FF vs Crop sharpness. APS-C is using 60% less glass surface, 60% less light for similar amount of pixels and therefore it produces softer images. It's like if you cut the top of a pyramid, you still get a pyramid, only smaller. So, sometimes FF corners can be as sharp as the center of an APS-C image. While the APS-C image isn't sharp from corner to corner just because it uses the sweet spot, it's the same "pyramid", only softer. FF sensor gets a lot less light in the corners due to stronger vignetting and this may be affecting the sharpness as well. For me, corner sharpness at f/1.4 is not that important, because most of the time corners are out of focus.
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