The angle the eyepiece’s circle of view covers for the eye, as stated by the maker: about 50° for a Plössl, 68° to 82° for a wide-angle design. The wider it is, the more it feels like looking through a big window. It is used to work out the true field.
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Related terms
- True field
The patch of sky actually visible in the eyepiece. As a first approximation it is the apparent field divided by the magnification: a 52° eyepiece at 50× shows about 1°, twice the width of the full Moon. The exact figure comes from the field stop.
- Eyepiece
The small interchangeable magnifier you look through; it sets the magnification. Its focal length is engraved on it: the shorter it is, the higher the power. The standard barrels are 1.25 inch (31.75 mm) and 2 inch (50.8 mm) wide.
- Wide-angle eyepiece
An eyepiece with an apparent field of 65° to 100° or more, using more lenses. At the same magnification it shows more sky, which helps when finding objects and following a planet with a Dobsonian. It is heavier and bulkier than a Plössl.
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