Reviews
Celestron AstroMaster LT 70AZ
70mm of refractor optics at f/10, weighing 7.2 pounds complete. It will show you Saturn's rings as a small sharp oval, and this page will not pretend otherwise.
By Scooter M. · Published · How we pick
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.
What 70mm allows
max useful magnification = 2 x aperture. Dawes limit = 116 / aperture.
70 x 2 = 140x. 116 / 70 = 1.66 arcseconds.
Celestron publishes 165x and 1.66 arcseconds. The resolution figures agree exactly. A box on the same shelf advertising 525x is describing an eyepiece swap, not an optical capability.
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.
Why f/10 is the right focal ratio here
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.
magnification = telescope focal length / eyepiece focal length
700 / 25 = 28x. 700 / 10 = 70x. 700 / 6 = 117x.
70x is roughly the magnification at which Saturn's ring separation becomes obvious, and it is available with an ordinary 10mm eyepiece. 117x from a 6mm sits just under the 140x ceiling. Which eyepieces to buy.
The maintenance case
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.
Where it falls short
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.
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| # | Telescope | Best for | Aperture | Price |
|---|---|---|---|---|
| 1 | No image Celestron AstroMaster LT 70AZTop pick70mm of honest refractor optics at f/10. It will show you Saturn's rings as a small sharp oval, and it will not pretend otherwise. | The smallest scope worth owning | 70mm (2.76 in)140x useful | Check price#ad |
image
Top pick · The smallest scope worth owning
Celestron AstroMaster LT 70AZ
70mm of honest refractor optics at f/10. It will show you Saturn's rings as a small sharp oval, and it will not pretend otherwise.
What the aperture allows
- Maximum useful magnification
- 140x
- 2 × 70mm of aperture
- Resolving limit (Dawes)
- 1.66 arcseconds
- 116 ÷ 70mm
- Cassini division (0.7″)
- Out of reach
- this aperture cannot resolve it
Celestron publishes 165x as this telescope’s highest useful magnification. Our figure is 140x, from two times the aperture in millimeters. The gap of 25x comes from the slightly more generous per-inch constant makers use. Neither number describes a typical night: the atmosphere usually settles the question well below both.
Worked example: a 25mm eyepiece in this telescope gives 700mm ÷ 25mm = 28x.
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 for this tube. Either way, a box on the same shelf advertising 525x is describing an eyepiece swap, not an optical capability.
At f/10 the long focal length does the refractor's classic favor: it is forgiving of cheap eyepieces and it produces high-contrast views of the Moon and the bright planets. Deep-sky objects are mostly beyond it, and it is better to know that going in.
Its published Dawes limit of 1.66 arcseconds means it will not split the tightest doubles or show the Cassini division. It will show the rings, four moons of Jupiter, the phases of Venus, and a lunar terminator that people remember for years.
What it does well
- Sealed tube: no collimation, no mirror cleaning, essentially no maintenance
- Light enough that carrying it outside is never the reason it stays indoors
- The f/10 focal ratio is forgiving of the budget eyepieces it ships with
- Genuinely good on the Moon and the bright planets, which is what most first-timers actually look at
What it costs you
- 70mm collects too little light for galaxies and most nebulae
- The alt-azimuth mount has no slow-motion control on the LT version
- Chromatic aberration puts a faint violet fringe on very bright objects
Skip this one if: Skip it if what you actually want is deep sky. No amount of eyepiece will make 70mm show you a spiral arm.
Questions people actually ask
Is a 70mm telescope worth buying?
Yes, on a stable mount. 70mm is the floor at which a telescope beats binoculars, and it shows lunar craters, Saturn's rings, Jupiter's four bright moons and the phases of Venus. Below 70mm a good pair of astronomy binoculars is the better buy.
What magnification does the AstroMaster LT 70AZ support?
The useful ceiling is 140x from two times the 70mm aperture; Celestron publishes 165x. With the supplied eyepieces on its 700mm focal length you get 28x from a 25mm and 70x from a 10mm.
Can you see Saturn's rings with a 70mm telescope?
Yes, as a clearly separated ring, at around 70x. What you cannot see is the Cassini division inside them, which spans roughly 0.7 arcseconds against this telescope's 1.66-arcsecond resolving limit.
Does the AstroMaster LT 70AZ need any maintenance?
Essentially none. The lens is fixed in its cell at the factory, there is no collimation and no mirror to clean, and a refractor needs almost no cool-down time. That is the main argument for choosing one over a larger reflector.
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