yeypiece field of view

[Gerald Sargent]

Can any one advise on how to, or wgere to find out how to,
get an approximate idea of the feild of view of an eyepiece
for a given telescope ? Thanks, Gerald.

[AstralTraveller (David)]

There are a number of methods, but I don't have all the details at hand.

The most common is to divide the apparent field of view by the magnification (assuming you know the afov). Magnification = focal length of scope/focal length of eyepiece.

Better is to measure the field stop diameter and apply a formula I've forgotten - someone else will know it.

Otherwise you can time the passage of a star on the celestial equator from one edge of you fov to the other through the centre of the fov. The star travels 360 degrees in (very close to) 24 hrs = 15 degree per hour = 15 arc minutes per minute. The hard part is making sure the chord crosses the centre of the fov. It's not too hard is you have an aligned eq mount but it would be a lot of trial and error on an alt-az.

[erick (Eric)]

Televue do a calculator which, as I recall, gives you this information. Of course, you can only choose Televue eyepieces to input!

http://www.televue.com/engine/page.asp?ID=107

Edit - not sure about that link. Go to www.televue.com and find your way to the eyepiece calculator on the eyepiece page.

[JethroB76 (Jeff)]

If you Google "eyepiece FOV calculator" or similar you will get plenty of options in which you can plug in your scope and ep details and get TFOV, exit pupil etc..

like this one
http://www.davidpaulgreen.com/tec.html