I'm looking for some advice. I've seen some Opteka lenses pretty cheap on ebay. I looked on the company's website and found a 650-1300mm f/8-16 listed at $299.95. I've searched google and can't find any reviews. Except for one guy on another forum that claims these seem to be same as Vivitar, I can find no user testimonials. Anyone here has experience with these lenses? It may be cheap compared to other lenses but $300 is a lot to pay for junk glass. Any recommendation?