Optics
The Maksutov-Cassegrain telescope (we’ll use Mak for short) is a type of hybrid telescope that integrates both mirrors and lenses into its optical design. A commonly seen example of this type of telescope is the Schmidt-Cassegrain by companies like Celestron, or SCTs for short. The optical design of both SCTs and Maks are quite similar, in the way that they use 1) a glass corrector lens at the front of the scope, 2) a fast primary mirror at the back of the scope, typically around f/2, and finally 3) a convex secondary mirror back at the corrector plate.
The Mak design allows for the corrector plate to be much thicker than an SCT for example, which unfortunately can be a major disadvantage, as it means that there is much more glass to cool down. The secondary mirror is just a coated section of the corrector plate (sometimes with differences in corrector figure), which means that collimation of the secondary mirror is unnecessary. This is an advantage over SCT’s, as on Maks there is no collimation required at all.
The specifications of a Mak telescope also require the tube to be a fair bit longer than say, an SCT, which means that the scope is a fair amount heavier. This allows for a longer focal length though, which can be very beneficial for planets.
The Orion 180mm Mak, as mentioned before is a Mak-Cass style telescope. This comes with some unique specifications compared to say a typical refractor or reflector telescope. In this portion of the review, I will discuss the technical specs of the telescope, and what they mean for you.
The aperture is 7 inches or 180mm. This is a decent size for the amount of light you are getting but is nothing extravagant or tiny; however, as said before, for Maksutov telescopes, 7” is quite a large aperture.
The focal length of this telescope is 2700mm, thus making the focal ratio (FL / Aperture) F/15. This is the main feature that makes the 7” Mak different from the competition, especially the F/5 and faster scopes astronomers have become accustomed to. Typical F/5 7 inch scopes would be about 1000mm long and have a focal length of 1000mm. Compare this to the Mak, which has a 2700mm focal length! The focal length determines how wide a field of view you can achieve (which is also dependant on camera sensor size, but we’ll assume that we use an identical camera.). A wide field of view allows you to capture larger objects in the sky, such as nebulae or constellations rather than being limited to smaller nebulae and galaxies with longer F/ratio telescopes. A smaller field of view, like the one you will get with the Mak, can be useful for targeting smaller deep-sky objects, or ideally lunar and planetary targets.
The Mak has an extremely small body, similar to that of an SCT Telescope. This means that you will be able to move the telescope around without much strain, as the length of the telescope is not much of an issue. It also weighs only 6.8 kg or 15 lbs, making it quite light for its aperture, which makes it easy on you and your telescope mount.
Mechanics
The Orion 180mm Maksutov-Cassegrain focuses by moving the primary mirror along a sliding rod inside the tube. Fortunately, this relatively small scope’s primary mirror is hardly heavy enough to cause much in the way of sag, making it largely immune to the issue of “image shift” which can be a nuisance when trying to focus at high magnifications or while imaging.
While the secondary mirror in the Orion 180mm Maksutov-Cassegrain is of course fixed to the corrector, collimation can still be adjusted with a set of recessed hex screws at the back of the tube, which tilts the visual back relative to the primary. You are unlikely to ever need to adjust this, but the provision is there.
A visual back similar to Schmidt-Cassegrains – but using a different, less standardized thread – comes attached to the back of the Orion 180mm Maksutov-Cassegrain. The newer model has a 2” visual back. However, the internal baffles of the telescope limit the fully illuminated field to about 30mm. A wide-angle 2” eyepiece will vignette to the point that there is basically no point in using one with this telescope. Your true field is limited to no more than about ¾ of a degree, or 1.5 times the angular diameter of the full Moon.
The bottom of the Orion 180mm Maksutov-Cassegrain is equipped with a standard Vixen-style dovetail to attach to a mount. A Synta/Vixen-style finder shoe is also bolted to the tube. There are provisions for additional dovetails and finder shoes to be attached via threaded holes drilled into the telescope tube.
Mount Recommendations
The Orion 180mm Maksutov-Cassegrain does best on a mount able to hold at least 25 lbs due to its heft and ultra-long focal length, with mounts such as the Celestron Advanced VX, Sky-Watcher HEQ5 being ideal. This is the case regardless of whether you plan on doing visual observation or imaging. We would not recommend using a mount without tracking for this scope.
Should I buy a Used Orion 180mm Maksutov-Cassegrain?
A used Orion 180mm Maksutov-Cassegrain can be a great scope, though you should make sure that there is no damage to the optics before purchasing. Fungus, corrosion to the mirror coatings or other damage are showstoppers to purchasing, but there is little else that can go wrong. Older units may only have a 1.25” visual back but as previously mentioned they cannot illuminate the field of a 2” eyepiece anyway and a 2” visual back can be found aftermarket if you must have one.
Aftermarket Accessory Recommendations
The Orion 180mm Maksutov-Cassegrain can handle even the lowest-quality eyepieces thanks to its f/15 focal ratio, such as goldlines, redlines, and cheap SWAs, although premium oculars are worth the additional cost. We recommend investing in a “low-power” eyepiece of 25mm or greater focal length, another in the 18-22mm range, another ocular between 12-16mm and a highest power ocular of 8-10mm focal length; the 180mm Maksutov cannot handle above 350x magnification even under perfect atmospheric conditions. The Explore Scientific 82-degree line of eyepieces, Baader Hyperions, Meade PWAs, or generic redline/goldline oculars are all great choices for this telescope. A 2x Barlow lens is needed for planetary imaging with the 180mm Maksutov and could be used in place of a high-power eyepiece for visual use. You’ll also need some sort of 1.25” or 2” star diagonal; we’ve outlined numerous options for either size. in our star diagonal buyer’s guide. Lastly, a UHC nebula filter such as the Orion UltraBlock will improve your views of nebulae with any telescope including this one.
The Orion 180mm Maksutov-Cassegrain can benefit from a dew shield, which not only prevents condensation from forming on the front corrector and thus fogging up the images and damaging the glass with trace chemicals present in dew or frost, but also reduces glare and improves contrast. Furthermore, it provides a physical barrier to avoid accidentally touching the corrector. A heated dew shield is unnecessary due to the thick Maksutov corrector plate cooling down much slower than a Schmidt corrector plate, which helps to keep it from getting far below ambient temperature; however, in order to achieve sharp views, you’ll need to give the telescope some assistance in cooling down to nighttime temperatures, as it can struggle on its own due to that thick corrector plate and its closed tube. Wrapping the whole tube in reflective insulation or installing a cooler that inserts into the telescope is almost essential due to how long it takes for the telescope to cool down to ambient temperatures without such methods.
Astrophotography Capabilities
The Orion 180mm Maksutov-Cassegrain has a long focal length, is not compatible with a focal reducer, and its limited field size further limits deep-sky imaging. As such it is not recommended nor particularly capable for deep-sky astrophotography
However, if cooled down properly, this telescope can provide excellent images of the Moon and planets when used with a 2x Barlow lens, a high-speed and high-resolution planetary video camera connected to a laptop as well as suitable capture software. It should be noted that any Barlow lens more powerful than 2x will take the telescope beyond f/30 which can be too extreme; alternatively one could consider using specialty 1.5x or 1.8x units if you lack the atmospheric conditions for 5400mm focal length to be worthwhile. A camera like the ZWO ASI224MC is ideal for the task of taking high-speed, high-resolution captures with the aid of software such as SharpCap or FireCapture and processing with AutoStakkert or RegiStax.
What can you see?
The Orion 180mm Maksutov-Cassegrain of course has an extremely long focal length, limiting its deep-sky viewing potential. However, smaller open clusters such as M11 and M35 appear great in this telescope. The brightest globular star clusters (such as M13, M3 and M15) can be resolved into individual stars. Excellent seeing conditions with the Orion 180mm Maksutov-Cassegrain will allow users to split thousands of double stars and see perfect concentric Airy disks. Planetary nebulae such as the Cat’s Eye or the Ghost of Jupiter display their turquoise or blueish colors with fine detail when viewed through the Orion 180mm Maksutov-Cassegrain. Galaxies can reveal some detail such as dust lanes under dark skies far from light pollution, but don’t expect too much with only 7” of aperture, while large emission nebulae like Orion (M42) and the Lagoon (M8) look great and are improved further by a UHC nebula filter but are limited by the 180mm Maksutov-Cassegrain’s claustrophobic field of view.
The Orion 180mm Maksutov-Cassegrain telescope is ideal for viewing planetary and lunar detail, being of course designed for the task. The phases of Mercury and Venus are easy to spot, while the Moon reveals its many fine details such as Rimae Alpes or Craterlets in Clavius with good seeing. Mars will show dark markings on its surface and its polar ice cap, with Phobos and Deimos visible if you’re lucky. Jupiter displays bright, colorful cloud bands, storms, and the Great Red Spot; its four large moons (the Galilean Moons) are resolved as disks with jet-black shadows during transits. Saturn’s rings and Cassini division can be viewed with the Orion 180mm Maksutov-Cassegrain; though the scope is too small to allow you to see the Encke gap without exceptional seeing conditions. Saturn’s brown and tan cloud belts along with its blue-gray poles can also be observed. Its moon Titan appears as a tiny gold dot and another half-dozen moons can be seen as star-like points. Uranus’ green-blue disk is distinguished clearly at high magnification but its moons are just beyond the light gathering power of this telescope. Neptune requires good seeing to be recognized as an azure ball rather than a fuzzy “star”; however, Triton should still be visible next to it even on mediocre nights. Unfortunately, Pluto is too dim to see with the Orion 180mm Maksutov-Cassegrain due to its increasing distance from the Sun and correspondingly decreasing brightness, requiring a 10” or larger instrument to be revealed at all.
