This is a follow on to JDM's two threads on the Vivitar solid cat, and the Sigma mirror, just to have a thread to discuss mirror lenses in general, vs. those 2 specific lenses. To start, I have always been fasinated by the mirror lenses. And like many, I could not afford a Nikkor 500mm mirror when it came out. But now that film cameras and manual focus lens prices have dropped, I finally have one . And I even used it to shoot tennis at my local high school, when I needed the extra reach. I am still amazed at how short the mirror lenses are, compared to the "stovepipe" simple telephotos. I estimate that my Vivitar 600mm solid cat is about or less than 1/5 the length of my brother's 600mm stovepipe. Rick's post about his Tameron Adaptall SP 500mm now has me curious about that lens. Although the next lens on my list should be the Nikkor 1000mm mirror.