(This post is from an email conversation with a friend. I thought the content might be useful for others.)
Q: [I am thinking about getting a telescope for my daughter. What should I get?]
A: I’ve spent a while looking at the current telescope options for your daughter. Here are some thoughts, probably without a lot of logical organization.
It’s easy to be deceived by marketing on telescopes. The most common thing is for cheap telescopes to be sold according to magnification. That’s totally the wrong thing to look for. The most important thing is the diameter of the lens or mirror, followed closely by the mount. (Just as an FYI, you can really only get about 50x per inch of diameter, so telescopes advertising 300x or even 600x are ridiculous. It takes a really big scope to get 300x or more, and only the best of atmospheric conditions.)
Diameter gathers more light and potentially better resolution. Focal length gets magnification, but generally works against the other important specs: angle of view and brightness. As far as diameter goes, I would try to get close to 6″ (150mm) for a reflector (mirror), or 3″ (75mm) for a refractor (lens). For focal length, it would be great to get 1000mm or more for a reflector, but a refractor may be quite a bit less. It would be good to get a scope that comes with at least two eyepieces. Usually something like a 25mm or so for a wider / lower power view (magnification is equal to the telescope focal length divided by the eyepiece focal length). And a higher power eyepiece around 8mm or so.
Telescopes are like most things – you make compromises. If you are interested in looking at stars / galaxies / star clusters / nebulas, then you generally want a telescope with a big diameter, shorter focal length, and a low-power eyepiece. But that’s a little more advanced than truly starter objects like the moon and planets. Planets and the moon need higher powers to see, and they’re relatively bright, so a smaller diameter is OK, but you want a longer focal length and higher power eyepiece. There’s no telescope that does both well.
And another misconception is that you want a telescope to look at stars. The truth is that stars are very boring. There is no telescope you will ever look through that is able show a star as anything other than a point of light. That’s really not very exciting. Clusters and galaxies of stars are interesting, as are nebula (dust and stuff from stellar explosions).
Most of the time, beginners like the thrill of seeing the craters on the moon or a planet. That wears out pretty quickly, though. And remember they don’t look anything like the pictures most have seen from Hubble and other modern huge scopes.
The next step, though, is stellar targets like galaxies and nebula. They can be pretty fun and there are dozens that are visible with modest scopes. That’s what will keep a person interested in using a telescope most of the time, since the planets are not always easily visible.
If I were buying something for a beginner, I would buy, in the following order:
Binoculars – Binoculars are the often overlooked best option for most viewing situations. They’re easy to use. They can reach a good number of galaxies, clusters, and nebula. The can still show decent views of the moon, show the moons of Jupiter, and, if you look carefully, show the crescent of Venus/Mercury and the rings of Saturn. A nice pair can be had for less than $100, and they can also be used for other stuff, like looking at birds.
Binoculars are described primarily by their power x lens diameter. A 7×50 pair means that they are 7x magnification and they have 50mm (2″) objective lenses. Once you get to 10x, you can’t hold them steady enough to be really enjoyable. If you get much below 50mm diameter, they are not well-suited for astronomical use. I recommend a pair of 7×50 binoculars. Here is a great pair for $73. Highly recommended! (I’m not sure if kids can really appreciate binoculars as opposed to a telescope, though.)
Low-cost, wide-field telescope with “Go-To” – This is a low-cost refractor (lens) telescope with GoTo that will (after pretty easy North and level alignment) automatically go to 1400 objects including all the planets. If you choose to go with a telescope, this would be a great choice. The relatively small diameter and short focal length mean that you won’t have great high-power views of the planets or bright views of the nebula and galaxies, but it should be an easy scope to use, and the price is right. Meade is a good quality telescope manufacturer. (Both of my telescopes are Meade, but I don’t have experience with their smaller scopes.) $250 is really cheap for a GoTo scope of any kind.
Low-cost, larger telescope with “Go-To” – This is a low-cost 5″ (130mm) reflector (mirror) telescope with GoTo. It would be the closest thing to a good compromise for both planetary and stellar viewing. It would gather more light for nebula and have a longer focal length for planets. It’s $400.
Hopefully among those three options you’ll find a good one to fit both your daughter’s interest and your budget.