I've always had a soft spot for Maksutovs. When I was a teenager, I dreamed about the exquisite Questar, far beyond my budget. In 1997, I bought a much more affordable Meade ETX90, which proved to have outstanding optics. A few years later, I acquired an Orion Argonaut 6-inch Maksutov-Newtonian, which is one of the finest telescopes I have ever used, and one I will never part with.
In 2001, Orion introduced a series of small Maksutov-Cassegrain telescopes: 90mm. 102mm and 127mm apertures. These were well designed, precision made, and excellent optically. Unlike some other brands, they were entirely made of metal except for the lenses and the rubber grip on the focusing knob. They were marketed under the StarMax brand for astronomical use and the Apex brand as terrestrial spotting scopes. One of their most striking features was a beautifully machined 1.25" visual back, threaded for camera T-adapters and perhaps something else. This resembled the visual back on Schmidt-Cassegrains, but had a different thread size. I was one of the early purchasers of the 127mm version, and I used this scope extensively, especially for solar, lunar, and planetary observing. In particular, I used it to observe transits of the planets Mercury and Venus across the face of the Sun.
In recent years, Orion has introduced two larger scopes in this series: a 150mm and a 180mm. The last is the subject of this review. Orion refers to this scope in their catalog as their "Big Mak," and it is a truly impressive telescope. I've been fascinated by this scope since it was first announced, and finally got a chance to test it extensively.
Once again, quality is everywhere in evidence. The lens cells are massive. The coatings on the primary and the corrector are immaculate. The focuser moves the mirror positively with almost no image shift. I could hardly wait to get the scope out under the stars and, as luck would have it, the skies were clear on the night I received the scope.
This scope is rather more specialized than most amateur telescopes. Its long focal ratio (f/15) and focal length (2700 mm) are reminiscent of the giant refractors of yesteryear. This makes it primarily a solar system scope. Because of the long focal length, high magnifications are readily achieved with relatively long focal length eyepieces: the shortest I used was an Tele Vue 11 mm Nagler (245x). The down side of this is that it's difficult to achieve low magnification and impossible to get a wide field of view. For example an Orion 24 mm Stratus eyepiece with an apparent 68° field of view yields a magnification of 112x and an actual 36 arcminute field of view, just barely large enough to encompass the Moon. Since the visual back accepts only 1.25 inch eyepieces, longer focal lengths give lower magnifications, but with no increase in apparent field of view.
On my first night out, I spent most of my time resolving issues with the Orion Sirius mount the scope was riding on. I did manage some fine views of the Moon at 245x, including spotting two of the craterlets on the floor of the crater Plato, a standard test for low contrast detail. I saw the domes west of Copernicus and the rille in Hypalus B. Turning to Saturn, again at 245x, the almost edge-on rings were like shaded gossamer, and their shadow formed a thin line across the planet's equator.
The seeing (atmospheric steadiness) was not as good on my second night, and there was a full Moon low in the southeastern sky. The five brightest moons of Saturn were readily visible, all but Iapetus forming a straight line. I tried some doubles like Iota Cancri, Algieba, and 54 Leonis, but was unable to split the close pairs of Epsilon Lyrae, largely because of its low altitude and the poor seeing. Despite the Moon, I was able to get good views at 112x of M44 (the Beehive Cluster), M67, and M57 (the Ring Nebula). At the end of the night, I used the "Park Scope" command to retain the mount's alignment. This allowed me to wake it up in two mornings later and have it immediately point at Venus, placing the planet well within the 24mm Stratus eyepiece's 36 arcminute field of view — very impressive!
On the night of May 14/15, I made a remarkable observation with this scope, a lifetime first for me. I was able to detect at 245x the transit of the shadow of Saturn's moon Titan onto the planet. Such transits occur only for a brief period every 15 years when Saturn's equatorial plane is aligned with the Earth. Although I've observed the shadows of moons many times on Jupiter, this was the first time I had ever seen the shadow of one of Saturn's moons. It appeared as a notch in the limb of the planet as it moved onto the disk. Unfortunately, Saturn was sinking rapidly towards my western horizon, and the seeing was deteriorating rapidly, causing the shadow to smear into nothingness.
A few nights later, with the Moon out of the way, I was able to spend some time looking at deep sky objects. Although this scope's rather narrow field of view prevents the wide vistas of the largest deep sky objects, it does very well on smaller objects because of its high contrast image. I found myself most using the Orion Stratus 24mm eyepiece (112x) and occasionally shifting up to the Nagler 11mm (245x) to tease out fine detail. The image was surprisingly bright even at 245x.
This telescope does particularly well with globular clusters such as M5 in Serpens Caput, and M13 and M92 in Hercules. The Ring Nebula, M57 in Lyra, was a fine sight. The many galaxies of springtime showed up well, such as M65, 66, 95, 96 and 105 in Leo and M49, 64, 87, 89, 98, 99, 100, and 104 in Virgo. I was easily able to see the galaxy M91 in Virgo, probably the most difficult of all the Messier objects. I also tried to split Epsilon Lyrae a second time, and this time succeeded thanks to better seeing.
My final acid test for this telescope was the planet Jupiter. This required getting up early in the morning. I used a pair of Orion Sirius 25mm Plössl eyepieces in my Tele Vue binoviewer with built-in 2x Powermate, yielding 216x. This was my first look at Jupiter of the season and, as I usually find, at first I could see hardly any detail. After a few minutes my "planetary vision" began to kick in, and more and more fine detail was visible. Towards the end of the session, as dawn began to light the sky, I could see the Red Spot Hollow rotating into view; the Red Spot itself was too faint to be visible as a color contrast. I had quick looks at the Moon, Venus, and finally Mars, still an incredibly tiny boiling disk far from the Earth.
In summary, I found that the Orion 180mm Maksutov, like any good telescope, simply got out of the way and let me observe a variety of objects with ease. While it seemed to lack some of the contrast of its smaller brethren, it made up for this with its large aperture, pulling in the detail when required. Because of its narrow field of view, it is not a general purpose telescope for everyone, but its huge image scale makes it a pleasure to use at high magnifications. I suspect it would also be a fine instrument for imaging the Moon and planets.
Geoff has been a life-long telescope addict, and is active in many areas of visual observation; he is a moderator of the Yahoo "Talking Telescopes" group.