Great shots, mxbianco! The Reflex-Nikkor you have used is the best performer of the Nikkor 500 reflexes.
It's great for handheld shots, very unconspicuous in crowded streets, and also for reaching subjects across a fence, but also for close-ups.
Defects: its own hood (HN-27) is only 2 cm deep and it's practically useless, but I found someone was tossing away on eBay a used hood(original, + original lenscap!) from a Hasselblad's 500mm Tele-Tessar, which can be adapted with a 82-86 step-up ring. So now my hood is 12 cm and flare is a thing of the past.
I also have an older 500mm C-type, focusses only to 4m and has more vignetting, not bad for astrophotography, maybe with a DX sensor (vignetting becomes negligible)
In my lens arsenal I also have the Reflex-Nikkor 1000/11 AI, difficult to use handheld (only when sun is really shining!), and a pain to focus (on a tripod, with LiveView it's OK)
I named this one
The ant's perspective, taken with 500/8 N and literally creeping in the high grass...
Ciao from Massimo
