The ETX range Ė its pros and cons
You can now get a whole range of telescopes in the ETX range Ė the ETX-70, a short-focus refractor; and the 90, 105 and 125, which are all Maksutov Cassegrains. These combine lenses and mirrors to give good optical quality and long focal length in a short tube.
There are big differences between the 70 and the others in the range, though they may all look about the same in the ads. The 70 is an f/5 refractor, which means to say that it will not stand very high magnifications. The optical quality is fine at low powers, but because of its short focal length it is not suited to giving the very best views of the planets though it will show you the major features of the bright planets. It is better at giving crisp, fairly wide-field views of star clusters and the brighter nebulae.
The 90, 105 and 125 Maksutov-Cassegrains have focal ratios of f/14 or f/15. This means that they will easily give higher magnifications, but as always if you have a high magnification you get a smaller field of view. So they are better for planetary viewing than the 70, but not so good for wide-field star spotting.
As a package ETX telescopes look very convenient. You simply point the telescope level and due north, tell it your location, the date and time, and it will automatically look for a bright reference star. Centre this in the telescope, repeat for a second star which it finds for you, and in theory it now knows where to find all the other stars, planets and thousands of deep-sky objects. But they have serious shortcomings which Meade have not addressed, even after several years on the market.
One major drawback with the ETX 125s, which I should mention, is that when slewing from star to star using their motors (as they do when using the Autostar GO TO system) they are very noisy indeed. You should not contemplate using them anywhere with other people nearby trying to get some sleep, such as in back gardens or on hotel balconies. Alternative ways to annoy the neighbours are to set fire to their dustbins or buy a Jack Russell terrier.
The ETX 70 is less noisy. I havenít tried the 90 or 105 alongside the 70, so I canít comment on them, though the ETX 105 at least is noticeably quieter. Noise is a problem with all GOTO telescopes, so be aware of it. However, just setting up the ETX-70 can be very frustrating. Unless you make sure that its base as well as the telescope is dead level to start with (a fact that is not in the instructions), you will have problems in finding the two reference stars. If your base is tilted by just a degree or two, each star will be well outside the field of view of the telescope (there is no finder) and you may spend ages trying to find each one. So you need to buy a finder, plus an optional spirit level, to find any objects.
Then there is the fiddly focusing knob, right at the back of the tube. Not too bad when the telescope is level, but when you are observing real stars instead of rooftops, the focusing knob is out of reach. Swap an eyepiece and you canít refocus Ė they donít make the eyepieces parfocal (which means that they are designed to be swappable without refocusing). So you need to buy the flexible focuser extension.
Another drawback is the ETX software, which I find staggeringly user-unfriendly given that these are meant to be starter instruments. Having told the telescope where it is and the time and date, you are then presented with lists of thousands of objects which you can observe. But these take no account of where you are, nor the telescope you are using. Try the list of double stars, for example. You are using an ETX-70 in London in October. You scroll through the list. Alpha Centauri. We have heard of that Ė the nearest bright star to the Sun, and an easily observed double star. But ask it to GO TO this star, and it will tell you that it is below the horizon. In fact you can never observe this star from London. So why bother to tempt you?
Instead, you might try to find the famous Double Double, Epsilon Lyrae, which is high in the evening sky. You will search for it in vain in the list of double stars. If it is there, I have not found it. I asked Meade where to find it, and the reply was that you have to go to Constellations, then find Lyra, then find Epsilon. I was given no explanation why arguably one of the best-known double stars is not on the list of doubles. And many of the deep-sky objects are unobservable with a telescope of only 70 mm aperture Ė particularly on its list of black holes!
I am pleased to report that an ETX 105 which I borrowed did usually find objects reliably. It usually placed them within the central third of the field of view of the 26 mm eyepiece supplied, which is all I could ask for. Being larger, the telescope is able to locate a larger number of the objects on the Autostar database, and the larger tube also makes it easier to get to the focusing knob when objects are overhead. It was also considerably quieter than an ETX 125 which I have tested. Its optical performance was good.
However, I really cannot recommend the ETX series for beginners hoping that the computer control will help them to get started. At the SPA's beginner's course in November 2004 several people attending with the express hope that we would be able to tell them how to start observing with their ETX telescopes -- clearly, the instructions supplied were not enough.
So what are their uses? The ones I have tried are optically good, very portable, and potentially useful. You pay a lot for the computer control -- for the same money you can get an ordinary manually operated telescope with considerably larger aperture which will give much more satisfactory views of most objects. They have lots of fans, and there is a detailed website devoted to them, though because it consists of user reports rather than being a carefully structured tutorial you may have to search hard for the information you need. So if you think that an ETX is for you, donít let me put you off buying one. Just be aware of their shortcomings.
The above is included in the interests of fair play! Actually, on an Autostar 497 handbox, as now supplied with ETX 90, 105 and 125 telescopes, once the telescope is set up you can enter any RA and dec by holding down the Mode button for more than two seconds, then entering the RA and dec required (using the scroll keys to change + into - if necessary).
I felt I had to write to defend the ETX. I bought one a couple
of years ago (ETX-125) and it's fine. I quite like it. I admit that the
AutoStar is lacking in one major area though... you can't (well, I haven't
found a way yet) enter the RA and dec of an object and make the thing GOTO it. Have I missed something? Other than that I'm quite happy with it.
Reply updated January 2005
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