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Celestron 21024 FirstScope Telescope Review

28 Feb 2019, 11:55 UTC
Celestron 21024 FirstScope Telescope Review
(200 words excerpt, click title or image to see full post)

Celestron’s FirstScope is probably the only usable telescope that I’ve ever seen that retails for under fifty dollars. However, usable does not necessarily mean good, and that’s what we’ll focus on in this Celestron Firstscope review.




The Optical Tube Overview



The FirstScope is a 76mm (3”) f/3.95 Newtonian reflector with a focal length of 300mm, and a spherical primary mirror. If you have done some basic research about telescopes you probably know that a spherical mirror won’t focus light correctly as a parabolic one does, and that is indeed the case with the FirstScope.Funny enough, if the FirstScope were 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 with the FirstScope is about 550 nanometers (1 wave), or 4-8 times the maximum tolerance for a decent telescope depending on who you ask. If you’re wondering why Celestron didn’t just make the scope longer, it’s because the material cost would go ...

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