Telescope/Eyepiece Magnification Chart

One of the most useful specifications you need to understand about your telescope is its highest or maximum useful magnification. This is the one number that is going to determine what accessories like eyepieces or Barlow lenses are a good fit for your device, as well as how much magnification can you shoot for before getting a blurry image.

Calculating your maximum useful magnification is relatively simple. You simply need to apply a formula using your telescope’s aperture as the base variable, however, why do the work when we have already done it for you.

How to use the magnification chart

The following chart will help you figure out two things

• What is your telescope’s Highest Useful Magnification according to its aperture
• What is the eyepiece size you would need to reach that magnification

For that second value, you will also need to know your telescope’s focal length. If you don’t know your telescope’s aperture and focal length, simply look up the model online, it should be pretty easy.

Once you have those values, simply look up the corresponding aperture and focal length in the table below.

We have used the most common sizes in the market, but if you have a telescope that doesn’t match exactly any of the rows below, simply look for the one that is closest, the resulting values should be close enough if your focal length varies by 100 or 200 or if the aperture varies by 0.3 inches or so.

For some of the smaller telescopes, the eyepiece size to reach max useful magnification would be 2mm-3mm. Since there are no eyepieces of that size, the minimum we are using is 4mm.