To my knowledge, the Reflex-Nikkor 500s were introduced like this...
- Starting in 1961, a 500 was sold as a 50cm f/5.
- In 1968 they were replaced by an f/8 “500mm”.
- In 1974 the 500s were given the C designation when they were given improved multicoating.
- In 1983 the C version was replaced with the N version, which was smaller, focussed closer, and produced better images.

I’ve owned a C for a few years and use it on my D300. The softness and low contrast don’t bother me at all because these “problems” are so easily corrected in image-editing software.

If you’re interested, I invite you to visit my review of the C version. It’s quite long, and very tongue-in-cheek in places, with sample photos at the bottom. You can find it on my blog here: http://hoaiphai.wordpress.com/2011/10/18/recumbent-review-the-mighty-reflex-nikkor-c-500mm-f8/
Tiny link: http://taii.cc/5x