How to check when buying a lens ?How to test the lens ?

How to test the lens in the shop ?

What's in the lens marking numbers denote f3.5-6.3?

The labeling designation of universal lens has f3.5-6.3.These designations are somehow connected with fotosiloy?

Which Soviet -aperture lenses ?

need for CANON 5D mark II

Whether the lens is suitable ?

I Nikon D3000 camera, I want to take him teleskopchik RMC TOKINA 3.5 / 70-210 for the Nikon, may suggest any good if I take it it's objective and is, well, if he is suitable to my camera ?