Yes, Sigma is a wide field telephoto lens, design for sport or nature photography. I have an 80mm f/5 APO refractor, have to throw some barlow's and high power eyepieces at scope to get some power out of it to see planets, specially Mars. Even than 200-250x is the most power I can get out of it in a good seeing night, while my old 4" f/9 Vixen/Celestron APO, easily can hit 100x/inch on a good seeing night.
I'm not a telescope builder, I don't know the prices of these ED glasses,
but they're just glasses to me. I think there's some scam going on, overrating these special glasses to charge more for the instruments.
I use to precision grind and polish YAG and Sapphire for high power lasers, much harder than any glass. Sapphire is all most as hard as diamond!Diamond powder the only thing that works on them for polishing/cutting.
My imaging skills are very limited, long time ago took some pictures of the planets with film, using 8" SCT! Not easy, specially focusing!
Astro imaging is another field , takes skill.
As I said, Nikon P900, not an astro camera, was not designed for it, but if one wants to show a kid the Moon or the other planets, it can be done.
Tried it with my Canon SX40 35x , don't work. Can't even get in focus on Jupiter, just show a blob.