How Much Magnification Do I Need?

by Stephen Baldwin

A question that comes up probably more than any other is "how much magnification do I need"? This is an extremely good question and one that requires some serious thought.

The single most widespread beginner's error is to use too much magnification. One should bear in mind that magnification has significantly less to do with astronomy than beginners imagine.

Astronomy is more about seeing faint objects, not about magnifying them and seeing faint objects is more about telescope aperture, in terms of mirror or objective size, rather than magnification.

Going over the top on magnification not only destroys image quality, it also makes your astronomy telescope much difficult to use. A guide for all optical devices is that as magnification increases, image quality,
image brightness, field of view and image steadiness all decrease.

Should you be having to deal with poor image quality with your telescope, and if objects are too nearly impossible to find (narrow field of view), or if the telescope shakes and vibrates too much, your magnification is probably way too high. This is particularly serious with regards to the numerous faint objects we want to see, since we lose image brightness quickly as magnification goes up.

"Maximum useable magnification" listings by a few manufacturers can be misleading. The amount of magnification you use is dependent upon a number of factors, the type of object being observed, viewing conditions of the , the size and quality of your telescope, your observing experience together with your individual preferences.

There isn't any miracle formula for determining maximum magnification for your optical telescope, but the often quoted guideline of 30-50x magnification per inch of telescope sizes as a maximum is the best place to begin.

Why use 30-50x magnification, rather than just 50x magnification?

The atmosphere is a important factor in deciding on exactly how much magnification one should use on any given night where conditions can change by the hour.

When viewing conditions are poor you will likely be down to around the 30x magnification or less per inch of telescope if you desire decent image quality. On other nights of very good steadiness, it may be possible to use 50x magnification per inch of telescope size.

Always remember, though, that the both the atmosphere and telescope mount limit magnification to approximately 300x magnification for any telescope, regardless of how large, and in many cases, will be rarely be used.

Should you wish to observe more, work with a larger aperture telescope, not more magnification.