September 17th: Top Ten Telescope Mistakes for Beginners

By on September 17, 2009 in

365daysDate: September 17, 2009

Title: Top Ten Telescope Mistakes for Beginners


Podcaster: Robin Scagell


Description: You’ve just bought your very first telescope, and you’re excited by all the wonders you’re going to see and the things you’re going to discover. But then – what’s gone wrong? Instead of sparkling stars, you see absolutely nothing! This isn’t uncommon, even with the very latest all-singing, all-dancing automatic telescopes. This show looks at the most likely things to go wrong, and helps you start seeing stars.

Bio: Robin Scagell is a British author and broadcaster on astronomy, and runs Galaxy Picture Library. He is Vice President of the Society for Popular Astronomy, and Chairman of the West of London Astronomical Society.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by the Salt Lake Astronomical Society.


Top Ten Telescope Mistakes for Beginners

A couple of times each year I take part in weekend courses for beginners in astronomy, and every time we go through the basics of setting of a telescope and starting to observe. Then, weather permitting, we go out and start observing. And every time, wouldn’t you know it, people call me over to help them because they can’t see anything through their telescope, and always it’s something simple. So obviously my powers of explanation aren’t very good. Perhaps I should stop right now and let someone else take over, but there’s no-one else around so you’re stuck with me.

First up, and favourite mistake by a long way, is starting with too high a magnification, which comes down to not knowing your eyepieces. Astronomy is full of numbers, and some of them seem to go the wrong way. Two is a bigger number than one, right? So how come a second magnitude star is fainter than a first magnitude star? That’s another story, but it’s true of eyepieces as well. A 10 mm eyepiece gives a higher magnification than a 25 mm eyepiece, even though it has a smaller number and usually is smaller as well.

Low magnifications are as useful when looking through a telescope as high ones, both for beginners and advanced observers. Three things happen when you increase the magnification. Obviously, things look bigger, but this means that the amount of light in the object is spread over a bigger area, so things actually look dimmer. And even worse, you see less of the sky, just like using the zoom when taking a photo. Even finding a big object like the Moon can be tricky using a high magnification. So the crucial thing when trying to find any object, is to start by using a low magnification, which means using the eyepiece with the largest number on it, generally 20 or 25 mm.

The next favourite mistake is not knowing how to align the finder telescope, the small device on the side that is there to help you find objects. It could be either a small, low-power telescope, or increasingly these days because they are cheaper, a red-dot finder. The crucial thing is to find something through the main telescope first, not the other way round, and it’s far easier to do this by day as you have a much bigger choice and can usually find something much more easily. Choose something quite distant and easily recognised – the end of a television aerial or antenna is a favourite. Keep this in the field of view of the main telescope and adjust the finder to show exactly the same point.

Some finders are very fiddly to adjust, and this is the biggest weakness of many telescopes, but at least by day you can see what’s going on and the object is not not going to move as the Earth turns, unlike objects in the sky. And, even with most computer-controlled Go To telescopes, you need to use the finder to find the reference stars, so this is a crucial step.

Back to night-time observing, and once you’ve found your object problem number three is getting it in focus. This usually applies to refracting telescopes which have a star diagonal to avoid you having to crouch down when observing objects high in the sky. Many refractors rely on the star diagonal to bring the eyepiece into the focusing range of the telescope, so if you can’t get anything to focus, make sure you always have the diagonal in place between the eyepiece and the telescope. Again, use the lowest magnification. The Moon should have a crisp edge to it, and stars should focus down to a point. If this doesn’t happen, keep listening for some tips.

I’ll assume now that you have started observing, but maybe you are unhappy with the view you’re getting. Something that isn’t always obvious is that you really do have to be outside to get the best views, not observing through a window. With binoculars you might just get away with it, but using a telescope that magnifies perhaps 50 or 100 times, even slight distortions in the glass will ruin the image. That’s mistake number four, and the next mistake is to take the telescope out and trying to observe straight away.

Unless you’re lucky enough to have a similar temperature outside as indoors, the telescope will usually be much warmer than the surroundings and it will have to lose its heat to the night air. This will cause currents inside the tube which will make the image hop around and refuse to focus, particularly when you increase the magnification a bit. Such poor seeing as it’s called can be caused by the atmospheric conditions as well, but you need to let the telescope cool down first. Leave it outside for an hour or so before observing, but with the optics covered, to give the telescope time to cool down.

A common problem is that you can’t see those amazing views of nebulae and galaxies depicted in colour on the telescope box. I won’t count this as your mistake, because there’s no telescope in the world that will show these deep-sky objects the way they appear in photographs. At best, even the brightest deep-sky objects appear as very pale fuzzy patches. But even allowing for that, people often have real trouble spotting what are meant to be easy-to-find objects. Maybe you even have a Go To telescope, and still can’t see them. It might be that the object is just too low in the sky. The lower down the object, the more atmosphere you’re looking through and not only the dimmer the view, but the brighter the sky background if there’s any light pollution at all, and in the case of planets, the greater the chance of a blurred image due to atmospheric turbulence. So wait until the object is as high in the sky as it can get.

That’s mistake number six. And mistake seven is to assume that all clear nights are the same. When it comes to deep-sky objects, you often have to wait for the very clearest of skies. Cold air from the poles, which you get following a cold front, is often the best, as cold air holds less water vapour than warm air. But you might find that misty nights are better for planets, and quite often really steady seeing is accompanied by haze. Some nights you have to give up on the deep sky and observe the Moon and planets instead.

And just as your telescope has to become adapted to the night conditions, so do your eyes. The next big mistake is to spend the time while your telescope is cooling down in watching TV or working on the computer. Screens contain a lot of blue light, and so do fluorescent and low-energy lights. Blue light destroys night vision much more than red light, so you won’t be able to see much for at least 10 or 20 minutes. A red rear cycle light is a great accessory for astronomers, as it will have much less effect on your night vision than a white one. Also try to avoid any lights in your immediate vicinity. Choose the darkest spot you can so you don’t have annoying lights in the corner of your vision. If necessary, put a cloth over your head to keep out all extraneous light. Who cares if you look stupid when you’re observing?

Still can’t see those faint fuzzies? Maybe you’re looking too hard! Mistake number nine is to stare right at the object you are trying to see. But your centre of vision is the least sensitive part of your eye. It has more of the less-sensitive cones which show colour and fine detail, but fewer of the rods which are more sensitive to light and occupy your more peripheral vision. So practice the art of averted vision, which means directing your attention away from the object, and looking all around the field of view.

Finally, and this is mistake number ten, know what it is you’re looking for. Get to know the sizes of objects. Don’t expect other deep-sky objects to be as big as the Andromeda Galaxy or the Orion Nebula. Many galaxies, such as those in the Virgo Cluster, are actually quite tiny, as are many planetary nebulae, even bright ones. This may be the time to increase the magnification. Not only does it increase the object’s size, it also darkens the background so faint and tiny objects might be easier to locate.

If after all this, you still can’t see the objects you’re looking for, now may be the time to suspect the telescope. Here’s a tip. The simplest way to start is to remove the eyepiece altogether and look centrally into the focuser. You should be able to see the circular aperture itself, with a circular shadow in the middle caused by the secondary mirror unless you are using a refractor. If things aren’t symmetrical, even if you’re sure you’re looking centrally, it may just be that the telescope needs attention. This is too big a subject for me to cover now, so instead I’ll refer you to my website,, for more telescope tips and a page all about aligning your telescope. Happy stargazing!

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at Until tomorrow…goodbye.

About Robin Scagell

Robin Scagell is a British author and broadcaster on astronomy, and runs Galaxy Picture Library. He is Vice President of the Society for Popular Astronomy, and Chairman of the West of London Astronomical Society.

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5 Responses to September 17th: Top Ten Telescope Mistakes for Beginners

  1. Cody June 19, 2013 at 4:08 am #

    Is this the same for when you look in the telescope and can’t see anything but, a little white dot in the lense? Even though the telescope has been outside to ajust to the tempature outside for atleast an hour or so…

  2. Hens Zimmerman January 8, 2012 at 7:30 am #

    I maintain a blog about getting more out of your (Celestron GOTO mount) telescope, so that might be helpful as well:


  3. Neil Nunes January 31, 2011 at 11:00 am #

    Hey it looks like I have fallen into about every one of these traps from trying too hard or taking my telescope outside and then wondering why the image is very jumpy, I never assumed it would be because it’s still warm, or because my eyes had not adjusted or a combination of both or even all your tips. Thanks very much for these great tips, I’ll try them all and see how I get on.



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