I see in your sig that you own at least two Intes Maks. Is it correct that these are no longer made? From my limited reading on those in CN, they seem to be the 'gold standard' for Maks, but rarely come up for sale used. Since you mentioned the SW/Orion 180, have you been able to compare with your Intes? I think the OP and I could benefit from your experience.
Bought my first SW 180mm Mak circa 2007, good but not perfect optically, sold and bought a few scopes in between, then in 2016 I bought a second SW 180mm Mak secondhand - a friend was selling it for a crazy price and it turned out to be optically perfect.
I've seen a few more of the 180mm maks in the field as well.
From these it appears the early ones (circa 2006-2010) had a few quality issues - some of the mirrors weren't as well polished as they should have been (a bit "grey" near the edge), and optically OK but not perfect if you are really critical at high power.
But the second one I had was optically as perfect as one could wish and I've seen other recent ones that suggest Skywatcher has resolved the quality issues.
The Intes M715 (or M715D) at f/15 appear very similar to the SW maks, but there are some slight differences:
1. Guaranteed optical quality. Intes supplied an interferometric test report with the 6" and larger scopes, and their standard quality was 1/6 wave P-V (or better) while the deluxe ones (the D suffix) were 1/8 wave P-V. Each scope has a serial number and this is shown on the test report. So buyers had a reasonable expectation of quality, which was not unreasonable considering what they originally cost (a lot more than the equivalent SCT).
SW/Orion/Celestron do not offer a guaranteed minimum quality, nor a test report, so you take what comes, though it appears in recent years they are consistently quite good.
2. The SW 180 is a Gregory Mak with an aluminised spot on the corrector. In star tests with a 7mm eyepiece, the SW mak shows some spherochromatism and the out-of-focus star images inside/outside are slightly dis-similar. Don't panic if you see this, it is normal - AT FOCUS it should be perfectly corrected.
The Intes maks are Rumaks, and have symmetric out-of-focus star images inside/outside focus and don't show noticable spherochromatism.
The Rumaks also have a flat focal plane, whereas in Gregory Maks it is curved, much like SCT's.
3. Some of the later Intes scopes had cooling fans added, SW maks do not. If you use insulation the cooling fans are not necessary.
4. Collimation on the SW maks is achieved with 3 pairs of push-pull screws tilting the primary mirror; the corrector and secondary mirror remain fixed. In the Intes Rumaks, collimation is by adjusting the secondary mirror (3 screws) much like an SCT.
5. Finderscopes. The SW maks have the usual finder shoe and an 8x50 supplied. Intes on the other hand used at least 3 different proprietary finder shoes - all incompatible - and supplied either a 6x30 or 8x50 finderscope with an engraved glass graticule, though the eyepieces were fairly poor.
6. Backend. The earlier Orion-branded 180mm maks with metallic gold tubes had a smaller rear aperture effectively limiting them to 1.25" eyepieces, while the Skywatcher "Black Diamond" ones (metallic black OTA) had a standard SCT back and could usefully take 2" accessories. The current Orion and Celestron ones are now the same as the Skywatcher version.
7. Weight and cosmetics. In this respect the SW/Orion/Celestron maks are distinctly more attractive being quite a bit lighter and more attractive than the Intes scopes. The only unfortunate aspect is the tube metal is so thin that bolted onto a Vixen rail they still can flex and you might consider retrofitting a rail with curved radius blocks.
8. Focusing. The SW maks are like an SCT - micrometer screw moves the primary and its smooth and easy to use. A little mirror slop may be evident, though not serious. The later Intes scopes (M615, M715, M815 etc) also have moving mirror focusing with a very different mechanism internally which is usually stiffer, but also has no slop. Some like it, some don't.
The larger aperture of the Santel MK91 scopes counts of course, on DSO's, and being a bit bigger mechanically, Santel were able to use a baffle affording a full unobstructed light-path to fill the 50mm focal plane. They also had deluxe-grade optical sets and I can see why Intes used the Rumak design - tight, perfect stars very similar to what you see in a premium APO. Fainter stars are pinpoints, edge to edge across the field. Visually in star tests in good seeing both the MK91 and the 10" APM appear perfect, as one would expect from optics at 1/10 P-V.
Observing wise... IMHO the novelty of wide-field low-power stuff wears off at some point and you begin to find there's no real issue with starting at 70X (the 180mm maks) or 90X (MK91 and my APM) and working up from there - provided you have a decent mount which tracks, and ideally either encoders (push-to) or a GOTO mount. The real bonus is finding what they can really do in excellent seeing which sets them apart. Aside from the planets, on close double stars, planetary nebulae and globular clusters they do not disappoint, and quite a few galaxies are within reach in dark skies, though obviously limited compared to a larger aperture newtonians.
With all of these maks I found effectively insulating the OTA is important to kill the internal thermal plume, and reducing the cooling rate means they also stay dew-free for quite a long time - in 10 years I might have used a warm hairdryer 3-4 times.
Edited by luxo II, 06 July 2020 - 08:07 AM.