Quote:
Originally Posted by By.Jove
And some Maks are corrected for coma astigmatism and field curvature, I gather, better than perhaps you give them credit.
Admittedly the f/ratio is not ideal vs CMOS sensors, but that also depends on the target.
Roland Christen did some with an AP 10” mak, several years ago with a CCD camera. Seeing and guiding will also be challenging.
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I give Maks as much credit as the laws of optics allow.
The Mak we are talking about looks like a Gregory-Mak although they probably aspherized the primary in order to eliminate coma.
Astigmatism is not a serious issue with this design but high order aberrations and field curvature can't be corrected.
It is possible to design flat field Maksutov astrographs but those designs require major departure from the classic Gregory-Mak configuration.
Quote:
Originally Posted by AlexN
I had an EXTREMELY high quality mak cass a long time ago, an Intes Micro 715. 7.1" f/15 2700mm F/L. Planetary and lunar views were phenomenal. Better than my C11. More "refractor like" with very strong contrast, the scope beautifully snapped into focus, and it was built incredibly, incredibly well.
I tested it with an APS-C sensor and a couple of much smaller sensors, like the Sbig st8-xmei, st-10xe, st-9xme etc, and the scope could only produce an acceptable image on the st9, sensor, which, if you're old enough to remember, was a 512px × 512px square sensor with gargantuan 20um pixels. The st8 was flat except the edges (where it was wider than the st9, however with its 9um pixels, the pixel scale was unwieldy. The st10 was sensitive enough to work well at f/15, however, it's sensor was bigger than the st8, and 6.8um pixels made it VERY sensitive to guiding issues. I ran that with adaptive optics to try to respond faster to inaccuracies in tracking, which worked well, but again, the field curvature was fairly extreme. At least 50% of the image was murky muddy blurs.
The qhy8 had no chance. The sensor was 4x that of the st10, so your target would be in the middle with a star trek like warp drive effect at the edges... 7.4um pixels and no adaptive optics option meant I was guiding with my st80, a 400mm guide scope is no match for a 2700mm imager...
In my experience, I'd say forget the mak cass. A mak newt however. That is a special scope and if you can get one at a reasonable price, I can't imagine any reason not too. Absolutely brilliant scopes.
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The superb performance of Maksutovs is anecdotal.
I suggest anyone with a good quality Mak to set up next to a good quality Newtonian of similar aperture and have a good look at the same targets and at the same magnification. You may be surprised that the Newt will win on the planets if it has good optics and the internal thermal plumes are dealt with.