Jethro, I don't get how an 80 mm f/15 Achromat with a CA index equal to 4,76 will "They are sadly out of Voque these days. Replaced by Super fast short Achros. "
No fast achromat will replace a 80 mm f/15 achromat, in terms of chromatic aberration, contrast and definition provided doublets (both scopes) have good figures! It's simple Physics!
On teh otehr hanbd you mention "My Altair Starwave Ascent 102 ED F/1122 has given me the very best views of the Moon and planets that I have ever seen.", Ok, no doubt about it, but now it's not an achromat but a semi-APO refracto debause de doublet has an ED element! So we're comparing two different leagues. Achoprs vs. Semi-APOs (ED doublets). That's not fair, IMHO!
Just my two cents!
Clear skies for us all!
A fast achromat will not replace an 80mm F/15 achromat.
However, a good quality 80mm F/7 FPL-53 apo/ed can certainly better it in terms of color correction, it is simple physics. An 80mm F/15 has a chromatic blur that's 2x the diameter of the Airy disk, The 80mm F/7 has a chromatic blur that is 0.75 x the diameter of the Airy disk.
Short focal length achromats are low power wide field scopes. 80mm F/15 achromats are high power, double star and planetary scopes.
A good quality 80mm ED/apo is both.
I trust Bomber Bob on this. He's an active member of the Classics forum and has tested many classic scopes using DPAC.
In my mind, the difficulty with these classic F/15 achromats is not the optics, though the fields of view will be quite narrow even with 1.25 inch eyepieces. The challenge is the long tube, it's about 4 feet long. Besides just dealing with the long OTA and the awkward viewing positions , the standard mount and tripods were not really up to the task, very shaky, wobbly. This is not a good thing, particularly for a scope that is used at higher magnifications.
Bob would know more than I but the Towa mount on my 80mm F/11s were marginal.
The 0.965 inch eyepieces are also an issue. One would want to upgrade to a 1.25 inch Visual back. Hopefully the standard Vixen 36.4mm visual back would fit, otherwise, it's a problem.
Scopes like this had their place and time. Now, it's a classic that can be enjoyed but it's not such a user friendly scope. I have owned several similar scopes and currently own a 60mm F/15 Carton. It's a nice reminder of how things used to be and why things are different today.