Comment by waerhert
I switch between the cheap Byomic 76/700 newton and my Sigma 600mm lens (Canon EF but using an adapter to fit the Olympus body). I tried to get the DSLR looking into the newtonian but it was just too heavy, causing the plastic focuser to simply bend way off axis. I've since bought a dedicated astro camera (Neptune C II) which fits alright on the newtonian. I'm keeping the Byomic 76 only for visual observations now. Looking to buy a proper refractor of around 480mm. The Sigma 600 does alright with the DSLR but isn't very sharp, hard to focus and suffering from some coma. It's good enough to learn the ropes for now.
Yeah, in astro, the quality of the lens shows in much more disappointing ways that regular photography. Any softness from the lens can be part of the art in regular photography, but in astro is a lesser image.
Maybe I missed it, but where in Europe are you? Are the temps part of your softness issue? I'm in Texas, and during the summer when it's prime time for central part of the Milky Way the seeing is horrible from the extreme high temps and the disturbance it causes in the air.
I've been looking at getting a dedicated astro camera as well to reduce that weight as well as free up the camera body to go back to its primary mission of time lapse. I've already gone down the rabbit hole deep enough to have a secondary scope and camera to use as a guide scope to overcome any of the slight mis-alignments during polar alignment. The hole is deep and easy to fall into. Be careful when looking down that hole wondering how far you'd be willing to go as you'll be deeper than you expected before you realize you've left the edge.