80 mm FPL 53 or 90 mm FPL 55 ?

[astrography_MC]

one of my friends is a little bit confused in between these scopes -

1.  TS-Optics PHOTOLINE 80mm f/6 FPL53 Triplet APO - 480 mm

2. TS-Optics CF-APO 90 mm f/6 FPL55 Triplet APO Refractor - 540 mm

 

which will be better for imaging ? not for visual.

Which glass is better for imaging , FPL 53 or FPL 55 ? Have anyone used either of the scopes? what is the performance of each of them? 

Please suggest.

 

 

Edited August 19, 2021 by astrography_MC

[johninderby]

FPL55 is very similar to FPL53 and apparently now easier to obtain. CFF seems to have switched over to FPL55 now.

From Stellarvue:

“Ohara FPL53 versus FPL55.  Investing in optical glass in large sizes is expensive and risky. Ohara is now making a new SD glass, FPL55. Based on the specs the only real difference between FPL53 and FPL55 is the latter can maintain its performance in larger sizes. So I will be making our new SVX180T using FPL55 since it appears to be a safer choice in this size range. 

Edited August 19, 2021 by johninderby

[Louis D]

FPL-55 is a newer, supposedly easier to work with glass than FPL-53 while maintaining a nearly identical Abbe number, 94.66 (FPL-55) vs 94.93 (FPL-53).  Both are way ahead of FPL-51 (81.54).  Either FPL-53 or FPL-55 will probably work equally well.

[astrography_MC]

then why the same 80mm FPL 55 is expensive than FPL 53?

[Louis D]

5 minutes ago, astrography_MC said:

then why the same 80mm FPL 55 is expensive than FPL 53?

Which two are you referring to?  It could be simple matter that the FPL-53 version is old stock bought at a lower price in the past while the FPL-55 version is new stock bought at higher, pandemic pricing.

[Andrew_B]

24 minutes ago, Louis D said:

Which two are you referring to?  It could be simple matter that the FPL-53 version is old stock bought at a lower price in the past while the FPL-55 version is new stock bought at higher, pandemic pricing.

It can also be related to different grades of glass. Apparently there is a wide variation in cost of a blank of any given glass type so it's possible that TS-Optics have specified a better quality of FPL-55 for their scopes to ensure better performance and fewer duds in the finished lenses.

I think your explanation is the most likely one though.

Edited August 19, 2021 by Andrew_B