Rather than provide only an overall five-star rating, it is more helpful to rate different aspects of a telescope separately. Also, because telescopes can be more than the sum of their parts, the overall five-star rating is not necessarily the average of the individual performance rating system. Here is how we rate individual aspects of telescopes in our reviews.

In addition to providing an overall out-of-five-star rating, we have ratings for different parts and aspects of a telescope that all weigh into the combined score. Telescopes are often more or less than the sum of all their parts. Here is an explanation of our rating system.

• Optics: The quality of the main optics (mirrors and lenses) of the telescope, and the consistency of quality.
• Focuser: How good is the focuser mechanism?
• Mount: Sturdiness of the mount, and either smoothness (if manual) or accuracy (if computerized).
• Lunar & planetary views: Is the telescope good for viewing the moon and planets?
• Rich Field: How good is the telescope for viewing deep-sky objects at low magnification?
• Accessories: The overall quality of the included accessories and how adequate they are for the telescope they are provided with.
• Ease of Use: How easy is it to use this telescope?
• Portability: How easy is it to travel with this telescope? What kind of vehicle does it need to be transported in, if any?
• Value: Is what you’re getting a good deal for the money? Is it affordable compared to similar alternatives, or is it a rip-off?

Telescopes without mounts will not receive a score of 1 for the mount; the mount score will simply not be counted. Telescope optical tubes sold with no accessories will be scored the same way.

A more thorough explanation of our rubric:

Optics

Optical quality is hard for beginners to determine, so we’ve gone and done that for you by testing the products we review.

• 1 star: Terrible at any magnification, worse than the unaided eye.
• 2 stars: Substandard, fuzzy optics, but enough to be somewhat enjoyable on the Moon and on deep-sky objects at low power.
• 3 stars: Not diffraction limited, but not unusable either, good to about 1x-1.5x per mm of aperture.
• 4 stars: Typical “good” commercial scope, not perfect but at least diffraction-limited and hard to immediately notice anything wrong with. 1/4th wave of spherical or other aberrations, or better.
• 5 stars: Absolute optical perfection; indistinguishable from perfect optics. Uncommon in a telescope, and very rare among most commercial offerings.

Focuser

• 1 star: Probably made entirely of plastic, it wobbles noticeably to the eye when focusing, enough to severely affect collimation. Struggles to hold heavy eyepieces or maintain focus.
• 2 stars: Wobbly, usually partly plastic or rough enough to make it difficult to find focus, but can at least hold focus and doesn’t affect collimation too severely.
• 3 stars: Acceptable focuser, but with some sort of flaw that can make it problematic—perhaps it doesn’t hold heavy eyepieces well, has unusual adapters, or is difficult to focus precisely.
• 4 stars: Focuser is all-metal, does not affect collimation at all, and is fairly easy to focus. It holds heavy eyepieces well.
• 5 stars: Smooth motion with a dual-speed adjustment of some kind and usually a focus lock, all metal and holds focus even with heavy eyepieces/accessories.

Note: Catadioptric telescopes have built-in focusers that shift the mirror back and forth, and as such, they don’t really have an external “focuser” in the sense that we can give them a rating.

Mount

• 1 star: Unusable mount; aiming at anything is frustrating. It can not even keep the Moon in the field of view properly at low power, or is too wobbly and shaky, or too unbalanced, to reliably aim at deep-sky targets.
• 2 stars: Mount is either shaky and unbalanced and difficult to reliably point at targets, but is not totally impossible to use. It can at least hold the telescope well enough to see something, albeit with a lot of frustration.
• 3 stars: The mount is usable but poorly constructed and/or undersized.
• 4 stars: Mount is stable, sturdy, balanced, and easy enough to use, but it has some design flaws that occasionally get in the way. It is simply not big enough for the telescope, or it is frustrating to aim precisely. If GoTo, it’s functional but not very accurate.
• 5 stars: Mount is well-constructed, properly supports the telescope, and balances/moves smoothly. There are no vibrations when focusing the telescope. If GoTo, the mount slews and tracks accurately.

Lunar & Planetary Views

High-power lunar and planetary observing combines all three of our previous categories in a sense: the optics must be good, the scope should be easy to focus, and the mount must perform well. Having a long focal length helps as well, because it means it’s easier to find affordable eyepieces that deliver high magnifications. Any telescope with good optics may be capable of showing great views of the Moon and Planets, but telescopes with longer focal lengths may be given a higher Moon & Planets rating to signify that the telescope was probably intended for this purpose. The mechanical design of the telescope, such as thermal management, also comes into play. Thus, our lunar & planetary rating correlates strongly with the optics, focuser, and mount but is not necessarily identical.

• 1 star: Poor optics guarantee this rating, as does a bad focuser or bad mounting.
• 2 stars: Telescope has mediocre optics or mounting, which make it unsuitable for high-power viewing; attempting high-power viewing may be possible but frustrating.
• 3 stars: Telescope has some sort of issue (shaky at high power, mediocre to poor optics, poor focuser, very short focal length), which makes high-power views less than ideal but not necessarily terrible.
• 4 stars: Telescope shows really nice planetary views but may still deal with some flaws, optical or mechanical, which can be worked around. It may need specialized eyepieces.
• 5 stars: Telescope has a good aperture, a long focal length that makes it easy to reach high powers, and an optics rating of 4 or 5. The mount is stable and does not vibrate too much. The focuser is usable.

Rich Field

Field of view relative to aperture. A small telescope with a wide field of view is fairly good for deep-sky viewing, whereas a small scope with a long focal length isn’t as good. A large telescope with a long focal length can somewhat circumvent having too narrow a field of view by having a 2” focuser, which makes it capable of a wider field of view for its focal length. Rich-field telescopes provide brighter, wider-field images, depending upon the eyepiece provided, which will usually have to be an aftermarket eyepiece. Because Rich Field and Moon & Planets ratings are both related to focal ratio, a good Rich Field scope might not be a great planetary scope, and vice versa.

• 1 star: Focal ratio is very long (>f/10 with a 1.25” focuser or >f/15 with a 2” focuser)
• 2 stars: Small aperture and a fairly long focal ratio (between f/7 and f/10 with a 1.25″ focuser, or between f/10 and f/15 with a 2” focuser)
• 3 stars: Ample aperture and a fairly long focal ratio (between f/7 and f/10 with a 1.25″ focuser, or between f/10 and f/15 with a 2” focuser)
• 4 stars: Focal ratio is moderate (f/5.1-f/6.9) but no 2” eyepiece capability or very small aperture
• 5 stars: Focal ratio is short (f/5 or below) and scope is either small aperture or has a 2” focuser

Accessories

• 1 star: Extremely low-quality accessories, e.g. eyepieces that are very low quality and/or encourage extremely high magnifications in a telescope which cannot deliver, plastic finders, etc.
• 2 stars: Bare-bones cheap accessories, which are usable but still of poor quality.
• 3 stars: Cheap basic accessories that work but aren’t the best (eg: erecting prism diagonals, partly plastic eyepieces, a red dot finder in a scope that needs a finderscope, or cheap Kellners).
• 4 stars: Useful, quality accessories, but one or two may need to be upgraded eventually or are lacking in something needed.
• 5 stars: Everything that is needed for good views is included with the telescope. No additional shopping is required immediately.

Ease of Use

• 1 star: The reviewer can’t even figure out how to use the telescope effectively.
• 2 stars: Extremely difficult to figure out how to use and constantly tough to use even once it is learned.
• 3 stars: Steep learning curve. Difficult to learn, easy to use after learning how. It’s probably a good scope, but a bad idea for a beginner.
• 4 stars: Gentle learning curve, but not entirely trivial. Easy enough to learn how to use after a night or two.
• 5 stars: Good for young children and technophobes. Telescope is simple to operate and easy to understand. It barely needs any instructions on how to use it properly.

Portability

• 1 star: Extremely heavy/unwieldy, individual components can injure someone trying to move without assistance. It really needs to be a permanently mounted observatory setup, or it needs a dedicated trailer to move.
• 2 stars: Fits in an SUV or other large vehicles, so it’s probably a bad idea to set it up yourself.
• 3 stars: Can fit in a car but takes up a lot of space in it. Individual components are easy enough to move around.
• 4 stars: Can fit in the trunk of a small-ish car or in a single seat in the car. The entire telescope can be picked up and carried in one piece.
• 5 stars: Would fit in carry-on luggage in an airplane. Can be picked up and carried with one hand without much trouble.

Value

• 1 star: There is absolutely no reason to buy this telescope, as cheaper alternatives are available that are superior in every way, and/or the scope is just terrible. There are other options that do everything this does at a much better price.
• 2 stars: There are other options that do most of what this does at a better price.
• 3 stars: Average value. Other options might be better, but it’s not a bad value.
• 4 stars: Good value, does more than other similarly priced items, or is cheaper than comparable items.
• 5 stars: Absolute best bang for your buck. It does better than anything else in its price range. There is no reason to go with anything else.

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