What is an ED eyepiece?

BBC Sky at Night Magazine's Scope Doctor Steve Richards solves your astronomy ailments.

The three most common designs of eyepiece you’ll come across as an observer: an orthoscopic (left), a Plössl (middle) and a wide angle (right). Image Credit: The Secret Studio

What is an ED eyepiece?

Steve says: “Eyepieces contain several lens elements and these are designed using different types of glass to correct chromatic aberration: unwanted false colours, halos and colour fringing.

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One type of glass that is particularly good at reducing chromatic aberration is known as ED glass.

ED stands for ‘Extra-low Dispersion’ and lens elements made from this type of glass reduce the distance between the plane of focus of the various wavelengths of light to produce a more saturated image.

Eyepieces with one or more ED lens elements produce more accurate colours, with less chromatic aberration than normal eyepieces.”

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Email Steve your astronomy queries to contactus@skyatnightmagazine.com and they could be answered in a future issue of BBC Sky at Night Magazine.