[davidmanze]

Given both are 24 MP sensors, you still have the advantage of longer FL on APS-C - or you're shooting at 400 mm with APS-C and at 600 mm with FF. I'm not too sure if the outcome will be that much different?

 I'm still a fan of the Tamron, at least on FF, on APS-c it's fine up to 450mm, yeah you can get get sharp (ish) results with a little PP boosting here and there at 600mm. However,the difference is clearly shown when using the Nikor 500mm F4, on FF it's just sharp, on APSc it's sharp (750mm)  and even when using the D7100's crop mode (1.3X=975mm) it still stays sharp, even at F4!

 So now if I'm muscularly geared up for carrying the weight, I change from FF to APS-c for FL changes you can't really do that with the Tamron!

 

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