So I have heard, but cannot verify that the TSA uses FPL-53 sandwiched between two IDENTICAL flints. In the case of the TOA objective, I’ve heard it’s two pieces of FPL-53 on the outside with a flint on the inside.
So now let’s go to “Telescope Optics”, by Rutten and van Venverooij, page 312. The figure there, and the text states, that to design the best doublet possible, you need to pick elements as far apart as possible, and as close to a horizontal line possible. However the two designs above are triplets, so let’s flip to page 324 and Fig. 21.21. Here and in the text it says you need to pick elements such that a triangle is created, with the largest area, for the best possible correction.
Now if the TSA and TOA have elements as stated above, they will not create a triangle at all, but only a line, like a doublet. Therefore, they cannot have any better correction than a doublet, and in that case, it makes NO SENSE to make a triplet at all.
And just for the record, of all of the triplet designs I’ve seen, they used three DIFFERENT glasses for the objective.
A long time ago, I was proficient in a DOS ray tracing program, and actually traced a 16 inch Buchroeder Tri-Schiefspiegler and an FPL-53 doublet. Currently, I don’t have the time or inclination to learn OSLO or ZEMAX. So what am I missing, if anything. This conundrum is driving me crazy.
Edited by SandyHouTex, 21 February 2021 - 02:39 PM.