Ever heard of mirror lens? Wow! Just found out about it today. Now, thus far, we have only been using, talking and reviewing refractive lens, nothing mirrored. Apparently, mirror lens offer absurdly low price-point lenses close to perhaps your monthly grocery allowance.
But as to how well they turn out in images, I have absolutely no idea yet...
Here, let me introduce to you the Bower 500mm F/6.3 prime for Nikon. It's ridiculous price tag of $180 is already making me want to buy it, shoot and throw it away after a few months, or after my event shoot! Well, to add in twice the fun, Sigma also makes such type of lenses. Hmm...sounds really like fun to me. However, here's a not-so-positive comments about Nikon D90 users attempting to use it though...
"After reading the Pop Photo article I was attracted to this lens as a good addition to my Nikon 18-200 lens. The lens was mostly what I expected but the Tmount form Celestron was terrible. It was loose and did not sit well on my D90. First suprise was you can not even use M exposure on the D90. There is no indication of over or under exposure so you can choose the shutter speed, it is all trial and error. Second big surprise is shot pix with the this lens and my 18-200 Nikon. Then cropped the Nikon shot to get the same cropping as the original uncropped 500mm shot. Surprise the Nikon cropped was better quality - sharpness, and contrast. I wasn't getting any advantage with the 500mm because what I gained in uncropped resolution I lost in contrast and sharpness.So the lens is going back."