What is a Plössl 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 a Plössl eyepiece?

Steve says: “A Plössl eyepiece comprises four glass elements arranged as two back-to-back achromatic doublets; or, in other words, two pairs of two glass lenses.

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These eyepieces produce a ‘standard apparent feld of view’ of between 50° and 56° with most set at around 52°.

This general purpose design gives good colour correction and an adequate feld of view at reasonable cost and they are often bundled with new telescopes.

On the downside, Plössls, especially at shorter focal lengths, suffer from short eye relief – a measure of how close to the eyepiece you have to place your eye to see the full feld of view.”

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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.