Night time filters to cut down the effects of light pollution appear to be relatively new ( found one article suggesting the first generally available ones were marketed in 2018).
Has anyone had experience with them? How effective are they?
The ones from "quality" filter manufacturers seem to cost around £130 for 77mm filter threads or 100mm square. So they appear to be a substantial investment, so real life experiences would be great to hear about, before making a purchase.