Odd business this. Interesting to see FPL-51 stated for the Raptor. There is that more expensive version that TS-optics sells that is stated to be FPL-53, but it seems us owners of the Sharpstar-branded model (whether doublet or triplet) are not sure what we have. Might even be some variation as SS have not committed themselves. Their web site just says: "Objective type: Triplet air-spaced APO (One element of the lens is made from ultra-low dispersion ED glass)".
And then there is this statement on the Agena web site:
"Please Note: In recent days, with the buzz around the Radian Raptor, we have received a few inquiries whether this scope uses FPL-53 glass or whether there are two optical versions of this scope in the market. Based on the information provided to us by Shapstar on Oct 3:
1) They use an ED element in this scope but they will NOT disclose what that glass type is.
2) Despite some speculation to the contrary in online forums, there is only ONE optical version of this scope worldwide. While some other international dealers state that this scope has an FPL-53 element, Sharpstar itself does not specify this."
Clear as mud. Not sure how to reconcile that information with user experiences.
While I believe that this statement sort of sounds plausible, TS is clearly stating that the telescope has FPL53. It would be completely misleading-downright lying to make that claim if Agena's statement is true.
I can only say that having purchased the TS version I don't see the level of CA in my pictures that is seen in this thread. It's there (lets face it, it's f4.5!) but not huge and a very slight correction in Lightroom is all that's necessary to fix it, which makes it a non-issue to me. It's either that my flattener spacing setup is more exact or maybe the filters being used introduce some false color. Overall I am happy with the scope, 61mm has its limitations but it's good at large field pictures which it was designed for.
Out of the box the scope did suffer from significant pinched optics (and associated CA that was quite noticeable) in very low temperatures but I have loosened the retaining ring as is commonly advised for most TS telescopes out of the box. It was extremely tight and hard to dislodge. Once it did the problem immediately became much less severe and now in warm weather it went away.
I don't know who is saying the truth, Agena or TS, either way it's a non-issue for me as the telescope performs as expected. None of the vendors is impartial so they will both claim something that's commercially beneficial to them. We can only judge the results.
(TLDR: if you have CA try to loosen the retaining ring, it caused pinched stars and worsened CA in my scope.)
Edited by licho52, 26 February 2021 - 07:41 AM.