I think I may have some - but do they really need to be f/15? Would f/12 do? I'll have to look as I can't remember exactly what FR they are - but they're in the range 12 to 15.
These are telescopes, so in cells - of sorts, and also in tubes if that's any use. See pictures. They are f/15 (f=900mm). One (blue tube) looks to be an air spaced doublet (you can see the spacers in one picture) while the other is more likely cemented. They have 0.965-inch plastic focusers at the other end.
I collected these with the intention of making a spectrohelioscope, but the price of H-alpha etalons came down enough so that I could buy one before I built the complex spectrohelioscope, so are now just sitting there. PM me if you are interested and we can come to some arrangement.
