A Mak Cass for DSOs? Has anyone used with success?
So the common Mak Cass telescope - say the Skywatcher 127 mm - is reputed to hold collimation a lot better than an SCT, are easier on the budget, and don’t have the hassles and additional costs (such as replacement focuser etc) required to get a GSO RC to work satisfactorily
However, the received wisdom is that the 127 MakCass is great on the moon, fine for planets but too slow and too narrow a FOV for DSOs.
While that may be true for nebulae, would a Mak Cass be any good for imaging planetary nebs and galaxies ?
The Mak Cass is a telescope and not an astrograph.
Sorry, but I like lecturing people about the difference between the two categories.
A telescope, to be worthy of its name, needs to be corrected only for spherical aberration and colour, which is not good enough for DSO imaging.
An astrograph, on the other hand must have all Seidel aberrations corrected, and those also include coma, astigmatism and field curvature.
However, for objects that are only a few arc minutes across, you should be ok with the Mak Cass, although the stars in the corners of the frame will not be the best.
Hope that answers your question.
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.
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.
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.
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.
Totally understand that, I wasn't comparing it saying it was better than a similarly sized quality newtonian, just that it was superb for visual observation of the moon and planets, and that visually it was closer to a refractor view than a typical reflector in terms of contrast...
I would also agree that the quality of the views of the Mak are occasionally blown out of proportion, however I wasn't using a meade or a skywatcher mak cass, it was a 3500 euro scope, and far superior to the mass produced units.
I completely concur though, If I were to buy a scope tomorrow it would be a big newt... no doubt about it. Unbeatable as long as they are reasonably high quality optics and sufficiently cooled.
Having had nearly all designs at one point or another, I can comfortably say for my use case, newtonians are my favourites, followed by refractors and then this list goes on from there. But, if I had nothing other than an sct, or a dk or mak cass, I would rather be doing astronomy with what I had, rather than not at all.
If you think your newtonians are so superior try telling all the SCT and refractor types they’re wasting their time.
It doesn’t mean you shouldn’t try, if you happen to have a mak (or SCT).
Many great images on Astrobin from cassegrains of all sorts - Maks, SCTs, Mewlons and more.
I think you misunderstood what I said.
A Newtonian has terrible coma and field curvature and it needs field correction lenses to make it into an astrograph, but for viewing or imaging the planets those aberrations are not significant because of the small angular size of the objects.
The lack of very good planetary images made with Maksutovs is only partly due to the fact that there are no large Maks available.
The lack of very good planetary images made with Maksutovs is only partly due to the fact that there are no large Maks available.
Couldn't resist flying the flag for my SW 180 Mak. I'm only a beginner, but in the hands of someone more capable I'm sure this scope would be capable of very good images...
I'm glad you posted your experience of using a high quality Mak for deep-sky. For quite a while I've been aiming to have a good crack at this myself, but I think you've saved me a lot of time and trouble.
As for mak-newts, I've been thinking of the Skywatcher MN190 but they are elusive. I got in touch with Andrews last June and they said stock would be available in Sept 2023, but I haven't followed up. It'd be good (but maybe expensive) if they were available again...
Couldn't resist flying the flag for my SW 180 Mak. I'm only a beginner, but in the hands of someone more capable I'm sure this scope would be capable of very good images...
You did very well but there is very little improvement that can be made from here unless you go to a larger aperture.
Unfortunately, it is impossible to break the laws of physics.
If you are really serious about planetary imaging, you should not go below 10" aperture.
With a good 10" scope you should be able to get bellow 0.5" resolution.
Cutting edge is around 0.2" for amateur imagers.
