I know this is a very niche part of the large pool of lens choices available to the K-Mount Shooter so hopefully this will add on to the knowledge available on the net. Hats off to hinman as well as others for their regular and comprehensive LBA postings! The Long and Short of It
I used to have one of those run of the mill Vivitar 500mm f8 mirror lenses a year back and it was everything that was said and not said on Amazon reviews. Not sharp, plagued by vignetting and the list runs on. I returned it not long after.
I came across the improved 500mm f6.3 variant on ebay and while I appreciated the improvement, I remained skeptical. There's no mention of this lens anywhere on the net w/ regards to user feedback..until I came across one right here on PentaxForums.com. That cleared up alot and even though the user review gave the lens a poor score, I decided to try it out anyways.
$180US later and some anxious waiting, it came.
The lens is huge. 95mm filter size huge. Its painted white metal surface very reminiscent of that found on "white glass" telephoto lenses. Weightwise, the lens ain't bad...around 700g...though on a K200D+Grip, it feels a bit back heavy. The focus mechanism is a bit stiff but smooth. Something that gave me pause was the plastic baseplate (the bottom piece that the supplied t-mount adapter screws on to). Feels pretty tight but was a little unsettling.
While resolution/flare would certainly favour more conventional lens formulas, the merits of Mirror Lenses are not without weight. First is size...well length more so. I only have a Tele-Astranar (Spiratone) 400/6.3 for comparison here but I can certainly tell you that I don't have any bag that fits it.
Another thing, the minimum focusing distance of the 400mm is around 6-7m while the mirror can work at distances of only ~2m away! Another defining trait is the lack of chromatic aberrations in the mirror lens. This is inherent to the design of the lens in that the 2 mirror pieces cancel each other out in terms of CA shifts.
The optical quality is noticeably better than the old Vivitar 500/8 I had. No vignetting problems. Its fairly sharp. I don't really have any comparisons but its kinda like budget telezoom. Not too sharp but not too soft either. The main issue with this lens is its large diameter. The large opening + inner cavity = high susceptibility to flare. You gotta watch your position relative to the sun's position. For the most part, the photos are noticeably improved shooting while standing in the shade/back to the sun. Sometimes a small boost in contrast in pp does nicely.
shot at close distance, better bokeh...for the most part.
Thus far, I've had a pretty favourable experience with this lens and while its not the sharpest assembly of glass around, it does well for its price tag and coupled with the length, would certainly satisfying the longer curiosities.
(More samples of the Rokinon 500/6.3 in action here.)
Last edited by FotoPete; 10-12-2008 at 09:51 PM.