Quote:
Originally Posted by Wavytone
I’d say you are using less-than perfect optics.
Firstly, real magnification tests are usually done using double stars and for these, to stand any chance at the Dawes criterion the scope must be working at about X3 per mm of aperture, or a tad more, in order to distinguish the difference between the Airy disk of a single star vs a double. Note in this the disks are overlapping- not separated.
This is a really tough test and to be honest I’ve seen very few modern scopes that can usefully resold at Dawes limit. It also means some of the antique old refractors from 150 years ago did have superlative objectives - while they were doublets, at f/15 or more some really were extremely good.
For your 80mm that suggests 240-260X so at 200X you are getting close to the useful upper limit.
But as for your achro... well you can join the dots. FWIW a while back one of the members of my club set up a classic Vixen 60mm f/15 achro refractor and it was simply perfect at high power - an excellent reminder of how good a long achro could be. On Jupiter I’d expect it matches your ED 80mm.
I have a 70mm quad APO which I’ve used at 160-200X on Jupiter, Saturn and Uranus. It does these surprisingly well for such a small aperture.
Extreme magnification is also the reason why I have my current scope.
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Thanks for your input. That's a mighty fine 70mm you have.
My brain was a tad befuddled by the cold last night when I got the 200X image looking good, or I would have gone and dug out my 2.5X Powermate and taken the power to 250X with a 5mm eyepiece to see what image that combination delivered.
If it stays clear I'll try that tonight, but depending on results, will have other eyepieces handy to go higher or lower power around your suggested range.
Regards,
Renato