Astronomy Buff

Why Magnification Doesn’t Matter

by Tony on January 3rd, 2007

Many people got new telescopes as Christmas presents. I know because many of you are asking me questions like, ‘How do I set it up?’, ‘What can I see with it?’ and ‘How Come I can’t see anything?’

It’s that last question I’d like to address for now. When I press someone further about how they are using their scope, it usually comes out that they are trying to view objects with their scope under extremely high magnification, around 150 power or higher. This is way too high to see anything easily. To use a telescope at this high of a magnification requires a rock solid mounting and tracking system, superior optics and a very steady atmosphere.

High power telescopes are essentially useless most of the time and looking through a telescope at high power is almost always a disappointing and frustrating experience. The best views are almost always obtained under low magnification, typically around 20-40 power.

I know this seems counterintuitive, almost all new telescope owners think that telescopes are designed to be used at the highest magnification possible. In reality, what telescopes are actually designed to do is collect light, to gather as many photons from very faint planets, galaxies, nebulae and star clusters and focus them on your retina or camera. The more photons the telescope can collect, the brighter the image will appear to your eye and you’ll be able to see more detail.

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Aperture, or diameter of the main mirror or lens, is WAY more important than magnification, all high power does is make things bigger and spreads out the available photons, making the galaxy or planet or whatever look even dimmer.

A telescope under high magnification magnifies everything, not only the size of the object your looking at.

• It magnifies the shakiness of the mount so much that a person walking by your telescope will seem like an earthquake in the eyepiece.
• It magnifies the mechanical imperfections in your telescope, when you try to turn the focus knob for example, the image of the galaxy may shift out of the field of view entirely if it is not a high quality focuser.
• It magnifies the atmosphere, under high power, the atmosphere is a seething, boiling cauldron that becomes nearly impossible to look through. Only under the calmest, clearest nights do I find decent views over 100 power.

Using a telescope at high magnification also makes things very difficult to find in the eyepiece because the field of view is so small. Imagine trying to find the moon while looking though a paper towel tube. Now imagine trying to do that while looking though a coffee stirrer. It’s hard enough to find what you’re looking for with the paper towel tube, and nearly impossible with the stirrer.

Finally, telescopes are just plain hard to use at high magnification, I avoid using mine at high power as often as I can, it’s just too much of a pain. Beginners are better advised to stay in the lower power range, typically in the 20-50 power range. Magnification is usually determined by the eyepiece used. Eyepieces are given a number corresponding to their focal length and are printed prominently near the top. To calculate magnification, divide the focal length of your telescope (in mm) by the focal length of your eyepiece (in mm) and you get the power of your optical system.

Telescopes are all about collecting photons, not magnifying things, and the in this situation, bigger is most definitely better. Large diameter telescopes at low power provide the brightest, most detailed images possible using your eye. For cameras and imaging it’s a little different, but for just learning to find things in your new telescope and simply appreciating the beauty of deep sky and planetary objects, put those high power eyepieces away. The number of times you’ll actually have the use for them are small.

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