The K 1000mm f/8 is an old school design but still a very sharp lens. It's a very large lens, about 15 lbs with cam, so needs a heavy duty tripod and a gimbal mount to balance on properly. After that you feel like a tail gunner swinging it around! Aside from the portability (or lack there of) I've taken mine to remote locations in the Everglades via kayak. It gives a reach of 1500mm with APSC and I found my K20D to be the limiting factor, not the lens (sensor too noisy above 800)! I've successfully used it with my Q also, and even with a 2x TC for a ridiculous effective reach of 11200mm!!
It's able to pull in distant details from many miles away provided you can focus it and the weather is good. There is some fringing on highlights, but not bad f/11 - f/13. The rack and pinion focus action is super smooth and very precise. I only wish that it had a focus lock screw!
See here for a trip I did with this lens: (scroll down to the lens)
Winter birthday triad on Florida Bay with the ‘Banana Boat’! | kayakfari ( kayak .. far .. i )
Another option is the 1000mm f/11 reflex which is a lot lighter and a lot smaller, hence will naturally get more use. I use a larger video fluid head and a medium duty pod, rock solid! The reflex is not quite as sharp as the refractor (to my eyes) but focuses much closer than the big gun. Excellent for moon shots, again with APSC cams like the 24mp KP (same pixel density as K-1) and an older Sony 16mp Nex-3N. This one also good for solar observation with a safety filter on the front. The reflex also has a bit of fringing on highlights, but the secondary mirror obstruction is comparatively small, so not too many donuts (unlike the 500mm mirrors!) which is nice! The KP is a huge improvement in higher ISO performance, and the K-1 MII will likely give similar results. Very well made lens, handles easy for what it is.
See here for reflex eclipse shots (also with a Q):
ART of Eclipses and other Cosmic alignments! | kayakfari ( kayak .. far .. i )
Here's the last 'pink' full moon with the reflex and KP:
The Coronavirus might stop our world, but can’t reach the sky nor the moon! | kayakfari ( kayak .. far .. i )
To sum up, lenses of this focal length are special purpose, you need to plan ahead to use them properly and successfully. Also you will probably need to do some PP to boost contrast (esp the mirror) and adjust colors. The reflex I'd recommend if you can get it at a good price. The big refractor get only if you're willing to lug it around, it comes in a big aluminum case. It will draw a lot of attention if you pull it out in public!