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I was asked "what would you recommend as a first telescope"

From Owen Gwynne

So, someone asked the above question via this website. My immediate response was this.

All telescopes are compromises between aperture (size) , magnification and bulk.

In an ideal world, you would want a telescope that had the largest possible aperture as that collects the most light and gives the brightest image.

Less obviously, you also want to consider the range of magnification you want. Now, most newbies would expect to go for the highest magnification possible, but in fact, you often appreciate lower magnification images better, because they have a wide field of view - a lot of what looks really good is actually on quite a large scale. So, for example - there are things called 'open clusters' of stars, which look really good if you can see them against the more sparse background.

In rough and ready terms, the figure to look for is the f/ratio; the higher the f/ratio the smaller the field of view, which can be annoying. However, a high f/ratio does give you more magnification for the Moon and Planets, though you can get the same effect on a low f/ratio telescope by using a different eyepiece.

The third factor is the physical size of the telescope - obviously, a large aperture will be bulkier than a small aperture scope, so if you have to travel to find a dark site, then a very large aperture or a very long scope will be less convenient. On the other hand, if you have a really dark sky, you will get a lot more out of a smaller scope than you would from towns.

There are several designs of telescope, refractors (the traditional telescope with a lens at one end and the eyepiece at the other) can give very good clear crisp views, but getting a large aperture rapidly gets expensive.

Reflecting telescopes can be larger for the same price, so the Newtonian telescope can be quite long - but generally has a lower f/ratio so gives lovely wide angle views. Don't get one that's too small as it misses the main advantage of offering larger apertures for the price.

There are other telescopes that have a combination of lens and mirrors (catadiotric) that can give less bulky telescope tubes, but these designs have high f/ratios so give a relatively narrow field of view. These are known as SCT (Schmidt Cassegrain Telescopes) or Maks (Maksutov) depending on the design.

Across the range of astronomy, there are lots of areas that people get interested in, and different telescope designs are often suited to one area than another. So, what I suggest is getting a good general purpose scope on the basis that it's your 'first' scope - as your interest develops, you may well find yourself geting a second scope that is more suited to your particular interest.

A commonly made recommendation is to look for a 6" or 8" Dobsonian telescope, and I would agree with this for you. A Dobsonian is a reflecting scope on a simple mount that you push around by hand. If you have that, a planisphere and an app like Stellarium on your phone or tablet, you can get a very good start in Astronomy.

You'll probably want spend a bit more on widening the range of eyepieces (often the ones that come with scopes aren't that great), but eyepieces are transferable, so will be usable in any other telescopes you buy in the future.

You may be tempted by telescopes with Computers and GOTO, all I can say is that I started with those, and they generally were the cause of most of the frustration I have had with the hobby. They take a while to set up, and if they don't work perfectly you resent the extra money you spent on that rather than on light gathering capability.

There can be benefits in having a telescope with a motor drive, but I'd say save that for the future.

Of course, the best advice would be to get in touch with your local friendly Astro Society.

So, that was my advice, what would you say?

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