2018 October 13

What telescope should I give a child?

David Arditti

I have had quite a bit of correspondence since the announcement of the existence of the new Equipment & Techniques Section. One question of particular importance that came my way was ‘What is the best telescope to get for a child interested in space?’

This is a question that is also commonly asked by members of the public at stargazing events. My answer of course will have a strong dose of personal opinions in it, and I welcome discussion on the subject. Patrick Moore always used to encourage children and other beginners to gain experience using binoculars first rather than hanker after a telescope. The counter-argument to this is that it does not usually stop them wanting telescopes. They can see a telescope is the ‘thing to have’ if you are an astronomer, and binoculars will not show you details on the planets, nor much on the Moon, without mounting them, which is quite a difficult issue to overcome in itself. Astronomical telescopes start with the big advantage of being mounted in some fashion.

So I will consider the most basic astronomical telescopes: those under the £150 mark. My tack with the potential purchaser, usually the parent, is first to explain the main practical issue with all telescopes: stability, and flowing from that, usability. It’s not obvious to someone with no knowledge that, the purpose of telescopes being that they magnify objects greatly, they will also magnify the slightest vibration and puff of wind, so that a telescope with an inadequate mount will have the image flying all over the place and it will never be possible to focus it on an object. Virtually all telescopes sold today are optically acceptable: they do work, but at the bottom end of the market, in my experience, the usual problem is just pointing them at an object and getting them to stay there, without jumping or swinging back, due to stiffness, lack of balance, or backlash in a poorly-engineered mount.

I do not recommend equatorial mounts for beginners. There are indeed some scopes on German Equatorial mounts (GEMs) within our stated price-bracket. But consider that a GEM is a complex, cantilevered piece of engineering, the telescope overhung on the tripod in two directions. To be stable, this requires a weight and quality of construction not possible in a beginners’ telescope. Moreover, most people are totally confused by GEMs, not knowing how to set up the alignment, balance them, or use the axes, clutches and slow motions. Most often you see beginners trying to point them by swivelling the whole GEM around the tripod-centre azimuth adjustment bolt, with the polar axis set at a crazy angle, and using the highest-power eyepiece they have, often with a Barlow lens as well, predictably failing to achieve anything.

If we exclude telescopes on GEMs, the telescopes currently available within our price-bracket group themselves into two categories: Newtonian reflectors in the range 75-130mm aperture on table-top mounts, and refractors in the range 60-80mm aperture on tripods. Some authorities do recommend the table-top reflectors for children, but I do not. I pose the question: how are you actually going to use this thing? If you put it on a table indoors, you won’t be able to see most of the sky. Also you’ll be looking through a dirty window, or freezing the house out in December. If you put it on a table outside, you’ll firstly find that most outdoor tables are quite unstable. Secondly, you’ll find if the telescope is in the middle of the table, the table is in the way, and if it’s at the edge, sooner or later the telescope will get knocked off and get broken. No, a telescope has to stand on the ground.

So we are looking at those with tripods. Unfortunately, most of those currently in this price bracket seem to be designed more with wildlife observation in mind than pointing at the sky, with altazimuth heads that resemble those of camera tripods. These simply do not work when pointing a telescope at a high altitude, because the azimuth bearing is outside the tube, and the tube will fall back therefore under its own weight, unless the bearing is clamped tight, in which case there will be too much backlash from the legs and whole structure to allow even initial pointing of the scope, let alone manual siderial tracking to keep the object centred. Another aspect of the terrestrial bias of design is the provision of erecting diagonals on these telescopes, unlikely to yield first-class images.

In fact there is only one telescope now on sale from UK outlets under £150 I can fully recommend. This is the Sky-Watcher Mercury-707 70mm f/10 achromatic refractor. I have tested this telescope and found it gives excellent star images and is genuinely usable in the field. It has an aluminium tripod that is stable enough and adjustable to the height of any user. The azimuth axis passes through the centre of gravity, therefore the telescope it can be pointed and will stay. There is a proper finder (not a plastic ‘red dot’ laser), a decent focuser and a star diagonal, and the supplied 1.25-inch diameter eyepieces of 10 and 20mm focal lengths, plus the 2x Barlow lens, give a sensible range of powers for this telescope of 28 to 140x. It’s great value for £79.

If the budget will stretch to a little over £200, 150mm Dobsonian telescopes represent superb value and usability for the beginner. Once again,

Sky-Watcher come up trumps here with their Skyliner 150P f/8 instrument. Such a telescope will take an enthusiastic beginner of any age a very long way. My other main piece of advice to first telescope purchasers is to go to a specialist astronomy dealer, not to buy from the general internet, or other source. Then they will get sensible advice, and decent after-sales service.

 

David Arditti Director, Equipment & Techniques Section