They won't be very sharp and you'll see donut shaped out of focus highlights. Also, 500mm on a 1.5x DSLR is a lot of magnification which will mean you need to keep it very steady.

What are you trying to do with the lens?

Regardless, you should stick with Minolta or Sony lenses. The big 3rd party manufacturers like Sigma and Tokina also make some good lenses but you need to pick and choose a little more carefully though.