At B & T we have eyepieces to suit every telescope
and every astronomer.
From basic eyepieces to the latest in eyepiece
technology.
Our Quality Brand name eyepiece selection come
from the world's leading eyepiece manufacturers and offer crisp sharp images
for your telescope.
Basic Eyepiece Information
The most misunderstood factor with telescopes
is that high power is better. Incorrect.
Sharp, Crisp images are far more enjoyable.
The information below may be helpful in determining
the eyepieces you choose. We hope that it does help you.
Magnification
To determine the magnification
Divide the focal length of the telescope (F) by
the eyepiece size. i.e. 900mm (F ) ÷ 25mm Plossl(eyepiece) = 36X
A maximum of 35X per inch of aperture will be
usable on the average night. 50X per inch on the exceptional night.
Field of View - Quick Calculation
Each eyepiece design has a different apparent
field (how big the field appears). This helps to determine how big the
true field of view (what area you really see) is.
Divide the Apparent field of eyepiece (see below)
by the magnification. i.e. (25mm Plossl) 50°Af ÷ 36x
= 1.38° or 83.3' arc minutes (multiply answer by 60)
Kellner Eyepieces have approx. 45° apparent
field (Af)
SMA or MA eyepieces have approx. 50°apparent
field (Af)
Plossl eyepieces have approx 50°apparent field
(Af)
Series 5000 Plossl eyepieces have a 60°apparent
field (Af)
Radian eyepieces have 60°apparent field (Af)
Series 5000Super Wide Angle eyepieces have 68°apparent
field (Af)
Radian eyepieces have 60°apparent field (Af)
Panoptic eyepieces have 68°apparent field
(Af)
Series 5000 Ultra Wide Angle eyepieces have 82°apparent
field (Af)
Nagler eyepieces have 82°apparent field (Af)
Field of View - Correct Calculation
Each eyepiece has a field stop. The "field stop"
is the ring in an eyepiece that limits the true field of view. You
need the size of the Field Stop.
The LINEAR diameter of the Field Stop divided
by the telescope focal length gives the TRUE field angle in space. Just
multiply that fraction by 57.3 to get the true field in degrees.