I've always liked fiddling around with widefield astro using old Pentax lenses, but most of the results were a bit underwhelming unless really stopped down.
Anyway, I chanced upon a YouTube video by "Cuiv, the Lazy Geek", about a month ago, featuring an Askar 200mm lens specifically designed for Astro photography. Here's that video:
https://tinyl.io/4u06
I made a snap decision to see if they were locally available and purchased one from Testar in Sydney. Only took a week for delivery. So far, no buyer's remorse at all. It's a magnificently constructed lens, 6 elements (3 ED) in three groups. Very smooth coarse and fine focussing rings with screw lock, and 12-blade f4 to f22 diaphragm, although f4 is the sweet spot. I'm no expert at photographic lenses, but I think this would give most similarly priced Canon and Nikon lenses a run for their money.
An M48 threaded interface with a built in M48 filter holder too! M48 to standard M42 adaptors and extenders are easy to come by as well, with standard 55mm back focus required. Here's Cuiv's latest comparison review:
https://tinyl.io/4u07
Not cheap, a bit over $1k, but if you want to do widefield, probably the most cost effective solution to good pics. I have mounted mine with an ASI2600 OSC on an old vixen GP + Synscan mount using an AzEq6 tripod I had, sitting on my front south-facing verandah, where I presently get great views of the SMC and LMC at civilised evening hours. The results have been most satisfying. Pic is 30x20s stacked and stretched in ASI Studio, no other processing.