I got to buy a second hand Clubman 50mm f/8 mirror lens from a second hand camera store and test it on the Gibbous Moon. Image quality is fair but nopt that sharp IMHO. my ETX90AT can beat this lens anytime. But for the compactness of this lens (just 3" in length and 72mm in diameter), it can't be beat! Using this lens require a tripod because of its slow f/8.
I plan to still keep this lens for total solar eclipse backup lens for my trip to China or Australia perhaps :) LOL