For a DIY lightweight apo project I am looking for a 100mm f5...f/7.5 apo objective lens.
I found
this 100mm f/7, but $1200 is a rather steep price tag as complete 100mm ED/APO telescopes can be gotten for under $1000. Probably less quality than FPL-53 but still (almost) apo.
Surplus Shed only has achros with the color fringes which is not my goal.
Where do the Skywatchers, William Optics-es get the lenses from ?