Celestron AstroMaster LT 70AZ

70mm is the floor of what is worth owning, and this telescope sits on it honestly. Celestron publishes a complete specification sheet for it, and nothing on this page requires an opinion about a view.

A 1.66-arcsecond resolving limit means the Cassini division, at roughly 0.7 arcseconds, is well out of reach. What is comfortably within reach: Saturn's rings as a separated ring, Jupiter's two main cloud belts and its four bright moons, the phases of Venus, and a lunar terminator that people remember for years.

The published focal length is 700mm at 70mm of aperture, which is f/10, a long focal ratio by beginner-telescope standards. That does two useful things.

• It is forgiving of cheap eyepieces. Simple eyepiece designs perform much better at f/10 than at f/5, so the bundled eyepieces show closer to their best.
• It reduces chromatic aberration. A simple two-element lens brings different colors to focus at slightly different points, and a longer focal ratio reduces the visible violet fringe on bright objects.

This is the real argument for a refractor and it is a good one. The lens is fixed in its cell at the factory. There is no collimation, no mirror to clean, and essentially no cool-down: point it and use it.

For a household that will not enjoy adjusting anything, that is worth the aperture it costs. Refractor against reflector sets out the full trade with the arithmetic, and the 102mm AstroMaster is the same argument with twice the light.

Celestron publishes 100 times the light-gathering of the human eye for this telescope. A 130mm reflector gives 345. That gap is the difference between the Orion Nebula as a gray smudge and the Orion Nebula as a shape with structure, and no eyepiece closes it.

The LT version also has no slow-motion controls, so tracking an object at 70x is done by hand on a simple alt-azimuth head. That is workable and it is less comfortable than a mount with fine adjusters.