Steve’s top tip

How do I work out the magnification of my eyepiece?

The magnification of an eyepiece is dependent on the focal length of the telescope that it is used with. Scopes with longer focal lengths provide greater magnification with a given eyepiece than those with shorter focal lengths. Conversely, eyepieces with shorter focal lengths provide greater magnification with a given telescope than longer focal length eyepieces.

You can work out the magnification of a telescope and eyepiece combination by dividing the focal length of the scope by the focal length of the eyepiece. An eyepiece with a focal length of 25mm used in a scope of 500mm focal length will have a magnification of 500 ÷ 25 = 20x.

Steve Richards is a keen astro imager and an astronomy equipment expert