Robtics | EyepiecesEyepieces come in different sizes, different optical designs and different focal lengths. Size wise there are two main standard sizes. Eyepieces with 1.25 inch (31.75mm) and 2 inch (50.4mm) barrel diameters. There are even eyepieces with 3 inch barrel diameter! Old style eyepieces measuring 0.965 inches (24.5mm) are not used for a very long time.

The main differences between optical eyepiece designs is aparent field of view (AFOV) and eye relief.

AFOV is the size of the viewing angle or image circle that can be seen while looking through the eyepiece. A small AFOV gives the impression of looking through a straw. A large AFOV gives the impression of looking out of an open window. AFOV larger than about 75 degrees do no longer show the edges of the eyepiece and you can really browse around with the eye. This almost adds another dimension to the image!

The AFOV is also the reason two inch eyepieces and large exist. The longer focal lengths and the larger AFOV's physically do not fit into 1.25 inch barrels and therefore low power eyepieces with a huge field of view are mostly only available in 2 inch.

Eye relief is the distance from the eyepiece within which the user's eye can obtain the full viewing angle. The higher the eye relief (+15mm) the better the eyepiece is suitable for viewing while wearing glasses.

Magnification is calculated by dividing the focal length of the telescope in millimeters by the focal length of the eyepiece in millimeters. A 25mm eyepiece gives 40x magnification in a telescope with a focal length of 1000mm (1000/25=40).

In this section you'll find a huge selection of astronomical eyepieces to complete your telescope setup.

Can't find what you're looking for or need help selecting the best eyepieces for you? Contact Robtics! We are happy to help!

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