Long focus lenses - Surplus Shed

[Merlin66]

https://www.surplusshed.com/pages/item/L3920D.html

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.

[Wavytone]

Also 102mm f/8.8 doublets, mounted

[Merlin66]

Nick,
The singlet long focus lenses are ideal for spectrohelioscope applications.

[Wavytone]

Hi Ken,

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.

[Merlin66]

Nick,
Misunderstanding....

Surplus Shed have been selling large achromatic doublets for the past few years. I had a 90mm and 70mm objective which were OK.

[Wavytone]

Hmm... If I was into grinding glass one of those singlet lenses could be a candidate to construct a 150mm Hamiltonian scope.

What stops me is that an ordinary f/8 newtonian is simpler to make and perfectly achromatic.