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Celestron 21024 FirstScope Telescope Review

Celestron’s FirstScope 21024 is probably the only usable telescope that I’ve ever seen that retails for under $50. However, usable does not necessarily mean good, and that’s what we’ll focus on here.

The Optical Tube

The FirstScope is a 76 mm (3ʺ) f/3.95 Newtonian reflector with a focal length of 300 mm and a spherical primary mirror. If you’ve done basic research, you probably know that a spherical mirror wouldn’t focus light correctly, like a parabolic one does, and that is indeed the case with the FirstScope.


Celestron Firstscope

Funny enough, if the FirstScope had a focal ratio of f/6 or so, thanks to its small size and shallow curve, it’d actually have a mirror close enough to parabolic as to work quite well. Even an f/5 would be passable. . . .

But an f/3.95 sphere simply doesn’t work well. The spherical aberration is about 550 nanometers (one wave), or 4-8 times the maximum tolerance for a decent telescope.

Celestron didn’t provide a longer scope because materials would be expensive. The increased box size and weight alone would make it impossible to market the FirstScope at its advertised price.

At f/3.95, precise collimation is critical with a Newtonian. Unfortunately the primary mirror sits on a plastic plate, which doesn’t allow collimation. You have approximately a fifty-fifty chance of the scope arriving decent-enough collimation to render a remotely usable image (well, as usable as can be with a one-wave aberrated mirror).

Celestron’s customer service is fantastic, and they’re happy to exchange your scope for a better one. Even if your scope arrives providing decent collimation, you need to be careful of knocking it out of alignment.

Oddly enough, the secondary mirror on the FirstScope is collimatable, but you’ll probably never need to adjust it.

The focuser is what you’d see supplied with most cheap, small, plastic rack-and-pinions, alone worth four times their price. I’m impressed that Celestron was able to put something this inexpensive, though I would rather have a bad focuser than uncollimatable and bad optics.

The FirstScope has no finder. You’re supposed to sight along the tube. With mere 15x, supplied by the included low-power 20mm eyepiece, this is easy enough. But it takes some practice.

The FirstScope’s tube is wrapped in vinyl, adorned with names of famous opticians, astronomers, and physicists found throughout history, which is a nice touch. This was originally done when the FirstScope was brought out for the International Year of Astronomy in 2009, to celebrate the 400th anniversary of Galileo’s first discoveries with a telescope, and Celestron has kept it in the decade since.

The Accessories

The FirstScope comes with two eyepieces. There’s a 20 mm Huygens with 15x and a 4 mm Ramsden “SR” with 75x.

The 20 mm Huygens barely functions. The apparent field-of-view is extremely narrow at 30°, and the view is fuzzier than expected with a good eyepiece.

The Huygens design adds some chromatic aberration (something one should never see in a Newtonian) to the view.

The 4 mm Ramsden is useless. It’s the same hated eyepiece that is supplied with Celestron’s Powerseeker line. It provides too much power for its scope (75x), the eye lens is tiny, has zero eye-relief, doesn’t perform well with a fast focal ratio, and it’s field is slightly more narrow than the 20 mm Huygens.

It also has an annoying tendency to get stuck in the focuser. The solution is turning the scope upside down, loosen the screws, and shake it. Preferably while above a garbage can, where it belongs.

You can pay more for an included “accessory kit.” This would include garbage Huygenian eyepieces, a useless 5×24 finderscope, and a cheap moon filter that doesn’t work.

Celestron also offers a Cometron version, a basically identical scope with far superior Kellner eyepieces, and a useless 5×24 finderscope. If that’s all you can afford, I’d recommend this over the what’s included, but with caution. The Orion FunScope is even better with both decent Kellner eyepieces and a red dot sight.


The FirstScope comes on a simple tabletop Dobsonian mount. Altitude tensioning can be adjusted with a hand knob, while the azimuth can be adjusted by tightening or loosening the nut in the middle with a pliers or wrench.

As to the smoothness of the mount’s motions. They’re good, but more or less irrelevant for a scope that’s probably not able to handle more than 40x.

How Useful Is Celestron Firstscope, Really?

But what can you really see?

Venus’ phases are visible. But forget being able to see Mercury as anything other than mush, if you can even find it.

You can see the moon’s craters, and with a fair amount of detail. Mars is a fuzzy and small red dot at best, at worst, nothing more than a star.

Jupiter’s moons are visible, and Jupiter itself is a small, cream-colored ball. With a higher magnification than the 20 mm eyepiece provided, you might make out equatorial band(s), but the Great Red Spot is invisible, as are many other features.

Saturn’s rings are visible at 15x. They look like ears sticking out of the planet, similar to how Galileo saw them.

If you’re lucky, at a higher power you might be able to see the rings in their true form. But most likely they won’t look great. Saturn’s moon Titan is also visible.

You can’t view Uranus or Neptune because they’d look like nothing more than a star, and you’d be lucky to get in the general vicinity of them without a finderscope.

As for stuff outside the solar system, anything besides the Orion Nebula, Pleiades and maybe a few bright open clusters are going to be hard to see. This is due to the scope’s small aperture, bad optics, and lack of a finder. Even the easiest double stars are difficult to split with the FirstScope.

Bottom Line

All in all, do I recommend the Celestron FirstScope?

Sort of. A pair of binoculars is better for most purposes. If you either are incapable of holding binoculars steady, or you or a loved one absolutely must have a telescope and can’t afford anything better, well, it’s better than nothing. But it’s blown away by nice binoculars, or a half-decent tabletop Dobsonian (with real eyepieces and a parabolic primary), or a cheap and small refractor. The Celestron FirstScope will show you more of the Moon and planets than binoculars can, but at the cost of being far more of a hassle for deep-sky viewing. All in all, it really comes down to what you’re after.

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