80mm ED Scope Opinion

[pbyrne]

Hi all

 

I am thinking of picking up an 80mm ED refractor and while cruising around the Web I came across this scope:

https://www.teleskop-express.de/shop/product_info.php/info/p8637_TS-Optics-Doublet-SD-APO-80mm-f-7---FPL-53---Lanthan-Objective.html

It states that the FPL-53 glass is mated with lanthanum glass as the second element.  FPL-53 controls CA very well, how will the addition of lanthanum glass improve the seeing?

I intend to use it purely for visual.

[johninderby]

It’s not as simple as what glass is used for the main element. It’s the combination of glasses that counts. My Stellamira uses the FPL53 / Lanthanum combination and it is noticeablely better for contrast and sharpness than a SW ED doublet. There is no noticeable CA at all. Of course it also depends on how well the objective is made. The Stellamira is a lot more expensise than the TS scope linked to though.

Edited July 25, 2020 by johninderby

[John]

If FPL-53 glass has been used for the ED element the chances are that a suitable glass has been selected for the 2nd element as well. FPL-53 glass is very expensive - there would be little point in using an unsuitable element to mate with it.

It is the combination of the two suitable glass types that controls the CA levels rather than just the ED element.