As I remember, the 500mm came out about the same time as the 1000mm. The UK magazine, Amateur Photographer did a test around about 1963 on the 500 and it wasn't at all bad. What struck me was the fact that it was a very simple lens with actually only 3 elements, of which 2 were cemented together and the two groups were at opposite ends of the tube. The 1000 was the same as the 500 but bigger, again the same optical setup.