View Full Version here: : Exit pupil & AFOV

22-04-2007, 11:31 AM
Sup guys.

I have another question! :screwy:

Say I have a 9mm EP, 42deg. AFOV...and a 9mm EP, 66deg. AFOV.

They'd both give my scope an exit pupil of 1.5mm. But what affect does the higher FOV have? Does it mean I will see a wider view within that 1.5mm? :shrug:

Thanks. Trying to get my head around these calculations!!


22-04-2007, 10:45 PM
Yes. Approximately, the actual field of view is given by the apparent field of view of the eyepiece, divided by the magnification that the eyepiece gives with the particular telescope.

So, let's say you have a telescope with 900mm focal length. Both eyepieces will give 100x magnification. But the actual field of view of view with the 66 degree eyepiece will be 66/100 = 0.66 degrees.

For the other eyepiece, the actual field is 42/100 = 0.42 degrees.

In other words, the actual field is around 50% wider with the 66 degree eyepiece.

If you can afford it, try for eyepeices with an apparent fov of 60 degrees or more. You can fit so much more in the field. And if you use a Dob like me, that means more time before the object moves out of the field of view.



25-04-2007, 01:42 AM
Great! Thanks for the info Morton! Much appreciated!