Surplus Shed have a special running at the moment on long focus lenses- 2500 to 4000+mm with apertures of 150mm.
These sound ideal for anyone considering building a spectrohelioscope.
I’m well aware singlets are preferred for that application - and suitable lenses are hard to find.
It was more that I was surprised to see SS had what appears to be a fairly respectable refractor objective that might interest someone keen to make a scope.