Could be a bit off topic, but you can get good, very wide field, narrow band images by using a short and cheap telephoto lens with a small-pixel sensor like the IMX183MM or IMX178. However, depending on the telephoto lens performance it may not really quality as "fast."
Here is a recent thread with some results from a $110 telephoto lens mated to an ASI183MM Pro camera:
Oh my, why did you assume i only as about very cheap lenses? i have Canon lenses that are being of top of the line but old models, have one new but that also became old but still a high class lens, so no, i wasn't asking about $100-200 lenses at all to be honest.
Also, the lens i want to really try to use is in this lens but it is version 1 not 2, can you find any mount ring for this lens to be used with ZWO/QHY cameras maybe? and how to mount this lens on EQ mount?
And what about this lens because i have this, it is F2 lens, say w will stop it down to about F2.8 or even f3.2, this isn't fast enough then?
I do have ASI290MM which has 2.micron, and later i will buy ASI174MM and next year i will add either ASI178mm or ASI183MM depends on what lens i will buy and what i already have, and my plan for getting 174mm and 178mm are for planetary and solar system imaging only and maybe use for guiding sometimes, but i wouldn't mind to use one of those into DSO if necessary.