Sigma 150-500mm focus sharpness at 500mm which focus to use?

Hi, guy it is truth Sigma 150-500mm at 500mm only can use the f8 or f6.3 but not f5.6 as it can't achieve the sharpness anybody or user of this len can advise, the len will mount on Nikon D5100 as as I can't found any information advise is much apprecaited.

I use this lens on a d300 but have used it on a d3100 as well. Works fine, only you're handling a lens with a camera dangling on the end. Same would apply for the D5100.

No clue what on earth you mean about aperture but sigma clearly advertises this as 150-500mm F5-6.3 which clearly specifies it's f6.3 at the 500mm end.

"as it can't achieve the sharpness"

That I don't get at all. Is it sharp at 500mm? Yes, quite sharp. You're not going to reach 500mm on nikon and get more sharpness unless you spend a lot more. When I went to buy mine I wanted to make sure I got a good one. Shot this and decided it was good.