Telescope Mounts, and Why They Decide Everything

200mm is a different category of instrument, not an incremental upgrade. Against the 70mm refractor at the other end of this list the light-gathering ratio is 200 divided by 70, squared: 8.2 times more light reaching your eye.

Two times 200mm gives 400x of useful magnification, which is more than the atmosphere delivers on all but a handful of nights a year. In practice this telescope is limited by the sky rather than by its optics, which is exactly the position you want to be in.

Dawes' limit at 200mm is 116 divided by 200, which is 0.58 arcseconds. The Cassini division, at roughly 0.7 arcseconds, is comfortably inside that. So is the Great Red Spot, and so are hundreds of Messier objects a 70mm scope simply cannot reach.

The honest cost is bulk. The tube is long and the base is wide, and this is a telescope you carry outside in two trips. Everyone who owns one tells the same story: they used it far more once they stopped storing it somewhere awkward.

102mm collects 2.1 times the light of a 70mm refractor, which is the ratio 102 over 70, squared. That is the difference between the Orion Nebula as a smudge and the Orion Nebula as a shape.

Two times 102mm gives 204x of useful magnification; Celestron publishes 241x. Its published Dawes limit of 1.14 arcseconds is short of the Cassini division, so expect the rings as a clean separated ring rather than a ring with a gap in it.

The short f/6.5 tube is the interesting part. It gives a wide true field for a refractor, which makes large open clusters and Milky Way star fields genuinely rewarding, and it keeps the tube short enough to be easy to handle.

Refractor maintenance is the real selling point for a household that will not enjoy collimating anything. There is nothing to align and nothing to clean.

Optically this is the same 130mm f/5 parabolic mirror as the StarSense DX 130AZ. Celestron publishes identical figures for both: 307x maximum useful magnification, 0.89 arcseconds of resolution, 345 times the light of the eye. The difference you are paying for is entirely in the mount.

What the motors buy is tracking. Once a planet is centered at 150x it stays centered, which changes the experience of looking at Jupiter from a series of nudges into an actual observation.

What they cost is alignment. Every session starts by pointing the telescope at two or three named stars, which means you need to recognize a few stars before the computer will find things for you. That is a real barrier for a complete beginner and it is the reason the phone-based StarSense approach usually suits a first buyer better.

The tripod is full height, so this is a stand-up telescope for an adult. That is a genuine advantage over every tabletop model here.

150mm sits in a genuinely useful place. Two times the aperture gives 300x of useful magnification and Dawes' limit works out to 0.77 arcseconds, so the Cassini division is within reach on a steady night.

Against the 8-inch it collects about 56 percent of the light. Sky-Watcher publishes the 8-inch as 78 percent brighter, which is the same comparison seen from the other side. Against a 100mm refractor it gains 232 percent, also their figure. Those two numbers together are the whole argument for buying by aperture.

The practical case for the 6-inch over the 8-inch is transport. It fits across a back seat, one person can move it in a single trip, and a telescope that gets used beats one that is technically better and stays in the garage.

This is a floor-standing Dobsonian, so unlike the tabletop models it needs no furniture. You sit on a low stool beside it, which is the most comfortable way to observe there is.

70mm is the floor. Below it a telescope struggles to beat a decent pair of binoculars, and that is a real comparison rather than a rhetorical one. Two times 70mm gives 140x of useful magnification; Celestron publishes 165x.

The defining number is the focal length. Celestron publishes 900mm, which at 70mm is f/13, an unusually slow ratio for a beginner refractor. A slow achromat brings the colors closer to a common focus, so the violet fringe on the Moon and on Jupiter is smaller than on a faster tube of the same aperture.

The same slow ratio narrows the field. At 45x with the supplied 20mm eyepiece, large star clusters that fit comfortably in a short refractor will not fit here, and finding things takes a steadier hand on the red dot finder.

It is also a large, heavy package for 70mm of aperture: a 685mm tube and a published 10.8 lb kit. That buys a steadier steel tripod than the lightest travel telescopes carry, and it costs portability.

Two times 102mm gives 204x. Celestron publishes 241x, and Dawes' limit is 1.14 arcseconds, which the maker's own figure matches exactly. At 1.14 arcseconds the Cassini division, at about 0.7, is out of reach: this telescope shows Saturn's rings as rings, not as rings with a gap in them.

The refractor advantage is that none of this needs maintenance. There is no mirror to collimate, no open tube for the air to churn inside, and the optics are sealed. Point it at something and it is already as sharp as it is going to be.

At 660mm the supplied 25mm eyepiece gives 26x and the 9mm gives 73x. Exit pupil at 26x is 102 / 26 = 3.9mm, which is bright and comfortable, and the widest field here is genuinely wide for a computerized telescope.

The 15.5 lb kit weight is the real argument for this one. It is the only telescope on this site that both finds objects by itself and can be carried outside in one trip without thinking about it.