The resolution is well above average, but only average contrast. This lens was introduced by Canon in September '78, shortly before they changed from the BL to new FD mount. Normally I would prefer the SSC version, especially with this lens, but it was a good deal. This is especially true with tripod mounted lenses where I might want to change camera bodies without removing the lens from the tripod. There is no color fringing, again a feature of a properly designed mirror lens, but there was a slight amount of astigmatism, which limited the resolution somewhat.
Price is good, and the optical performance is excellent.
You lose almost 2 stops of light and focusing ability with the 500, but it costs less than half as much. I was glad I took the 500 as it packed really well due to its very light weight and relatively compact dimensions. One could always wish for more speed, but in daylight, this is a very useful lens. It was in SB Mint condition, with case and everything. Problem was, I was dissapointed with the optical performance.