The Optical Tube
The Celestron 700, or C700, is a Maksutov-Cassegrain (the 700 seems to denote that it’s a 7” or 180mm telescope) and is identical optically to the Orion and Sky-Watcher 180mm Maksutov-Cassegrains that have been offered for years. The optics in these scopes are extremely high-quality and will provide much sharper and higher-contrast planetary, lunar and double star views than your typical 6-10” Newtonian or Schmidt-Cassegrain. However, that performance comes with a financial and practical price.
At a focal ratio of f/15, this telescope is not going to provide sweeping, wide-field vistas of the heavens – at most, you can just barely squeeze out a 1-degree field of view (about two full Moons) with a low-power 2” eyepiece, and as a result, the telescope feels a bit claustrophobic compared to an 8” Dobsonian or Schmidt-Cassegrain, both of which can provide significantly wider fields of view. The f/15 focal ratio and 2700mm focal length also mean you simply will not be doing deep-sky astrophotography with this telescope, as the exposure time and tracking accuracy required are simply too much to be worthwhile or for the Advanced VX mount to achieve.
Additionally, a Maksutov-Cassegrain of this size has a rather thick corrector plate. Your average 8” Schmidt-Cassegrain already can take a decent amount of time to cool down when brought outdoors into cold temperatures, and a 7” Maksutov-Cassegrain needs even more thanks to the thickness of the corrector, which retains heat much more than a Schmidt corrector plate and traps in the warm air from the cooling primary mirror as well. You can solve this via a DIY cooling system or a Lymax CatCooler, but the former is complicated to make and the latter are no longer available new, plus either is yet another gizmo to toss in your accessory case, power and remember to use. Wrapping the telescope in Reflectix also helps, but then your pretty optical tube looks like it’s covered in tin foil and bubble wrap. The corrector plate of the C700 also attracts dew, and if it is properly cooled with one of the aforementioned measures it will do so rather quickly, so a dew shield is somewhat mandatory with this telescope.
Like a Schmidt-Cassegrain, focusing the C700 is accomplished with a knob on the back that moves the primary mirror back and forth. Thankfully, there is little to no image shift from the primary wobbling on the focusing rod in the C700, probably due to the excellent quality control these scopes receive. The rear of the scope uses a proprietary thread that does not match those on the back of Schmidt-Cassegrain telescopes, so you’ll need a special adapter if you want to use anything besides the stock 2” visual back (which will suffice for most purposes). Being a Maksutov, the C700 doesn’t usually need to be collimated, though there are some collimation screws in the back to adjust the primary.
The C700 attaches to the Advanced VX with a Losmandy or D-style dovetail plate, which provides a more secure and stable connection than a smaller Vixen plate.
The Advanced VX 700 is relatively lacking in accessories, though what the scope does include is plenty nice, and if you have the kind of budget to buy it in the first place you should have enough left over to budget for extra accessories.
The Advanced VX 700 includes a 2” visual back and 2” mirror diagonal. Neither is of a compression ring design but both work very well and it’s quite rare to see any telescope including 2” accessory compatibility out of the gate.
As for eyepieces, you only get one – a 28mm L.E.T. eyepiece, which seems to be some sort of a modified Kellner. It provides a magnification of 73x, an apparent field of view of about 60 degrees, and a resulting true field of around 0.8 degrees, a bit bigger than the full Moon. The L.E.T. works great as a low power eyepiece, but for high-magnification views of the Moon, planets, and double stars, you’re going to want some stuff at shorter focal lengths.
The 700 also includes a 9×50 finderscope, which is more than adequate for aligning the GoTo system of the mount.
The Advanced VX Mount
The Celestron Advanced VX gets different reviews depending on who the audience is. Serious deep-sky astrophotographers hate it because of its poor guiding accuracy, incompatibility with ASCOM or EQDIRECT, cheap servo motors, and the low quality of the declination axis bearing in particular. Casual astrophotographers and those who do electronically assisted astronomy generally tend to like it as it’s cheap, beefy, and easy to learn how to use. Visual observers love it because it’s inexpensive and will hold plenty of weight.
Since the C700 is used for the latter two of the three aforementioned categories, I think it stands to reason that for what it’s being used for in this case the Advanced VX is a great mount. It’s easy to use, holds the C700 optical tube plenty steady and if you want to do some casual astrophotography with a different optical tube such as a small refractor, it will work just fine. As for use with the C700, the Advanced VX’s tracking accuracy is plenty good for visual and planetary imaging work, and the Celestron solar-system alignment feature allows you to get observing as soon as you can get a rough polar alignment and spot the Moon or a planet in the sky.
The only thing that significantly bothers me about the Advanced VX mount itself is that it doesn’t come with a polar scope. For casual observing, you can get away with simply pointing north and setting the latitude adjustment accurately, or attempting to sight through the polar scope hole, but if you want to image the planets or moon for hours at a time the tracking will build up with inaccuracies quite fast and result in your target drifting out of the field of view if you do not properly align with a polar scope. A polar scope doesn’t cost a lot of money, but it’s yet another thing to remember to go out and buy and I wish Celestron would just include it with this telescope.
Should I buy a Used Advanced VX 700?
If you can somehow find one of these telescopes used, I’d absolutely recommend buying it.
For the same price as the Advanced VX 700, there are some other options you might want to consider:
- Celestron Advanced VX 8” Schmidt-Cassegrain: Slightly more aperture, wider field of view, faster cooldown time, and a bit more useful for astrophotography
- Celestron NexStar Evolution 8: Slightly more aperture, wider field of view, faster cooldown time, and more convenient to set up and use
- Sky-Watcher 12″ Flextube SynScan: Considerably more aperture, easier to use, wider field of view.
Aftermarket Accessory Recommendations
There are a number of useful accessories that we’d recommend picking up for this telescope. The first is a few good eyepieces. The C700 can handle up to 350x, which corresponds to about an 8mm eyepiece. For this high-magnification category, we’d principally recommend the Meade 8.8mm UWA, which provides 307x and a field of view of 0.27 degrees. For medium power, the Meade 14mm UWA (193x and 0.425 degrees) or Celestron Luminos 15mm (180x and 0.45 degrees) would make a splendid choice. And to achieve the maximum possible field of view the C700 can provide, the Astromania 56mm Plossl makes a great budget pick, achieving 48x and a field of view of just about one degree or two full Moons wide.
Another major consideration for this telescope is a power supply. If you’re at home an AC power cord will work just fine, but a marine battery or, even better, a dedicated power supply such as the Celestron PowerTank Lithium is a great choice.
Lastly, of course, the Advanced VX really needs a polar scope, which is available from Celestron.
What can you see?
The Advanced VX 700 excels at lunar, planetary, and double star observing. Jupiter and Saturn will show their glorious cloud bands, Mars’ albedo features, and polar ice caps are visible at and around opposition, and the phases of Mercury and Venus are visible. Uranus and Neptune, of course, appear as tiny bluish dots as with any telescope. Additionally, the Moon will show craters, ridges, and a multitude of other features down to a resolution limit of around 1.5 miles (2.4 kilometers).
Outside the Solar System, the C700 is still capable of doing a lot despite its limitations. With 7 inches of aperture, it will do a good job at showing you the brighter deep-sky objects, especially globular clusters, and planetary nebulae, but the scope’s 2800mm focal length means it will struggle to fit large nebulae such as the Orion Nebula or galaxies such as Andromeda in the field of view. The C700 is also capable of splitting double stars as close to 0.6 arc seconds apart.