Here's an example of what I've done in green. I have included plugin author Timothy Reaves' comments and instructions from the module.ini file.
name = Ocular
author = Timothy Reaves
contact = *deleted for this Cloudy Nights post*
description = Shows the sky as if looking through a telescope eyepiece.
load_at_startup = true
# For each eyepiece, create a group name ocularX, where X is
# an interger in the range 0-9. For each group, add:
# name + A string to identify the ocular. Optional.
# afov = the apparent field of view for the eyepiece in degrees.
# efl = the focal length of the eyepiece in mm.
# sfl = the focal length of the scope in mm.
# flip = [h|v] flip the eyepeice view horizontally & vertically : optional
# Example for Nikon 12x50 Action Extreme with a stated 5.5Â° FOV:
name = Nikon 12x50 Action Extreme
afov = 66 # TFOV 5.5Â° x 12 = 66
efl = 1
sfl = 12
# Comment: flip = [h|v] is not needed for binoculars
Yup, that easy!
I have compared the result with 5.5Â° finder circles in both Hallo Northern Sky (hnsky) and Cartes du Ciel (CdC beta ver 3). Allowing for the visual differences in the programs and star catalogues used, the FOV window is practically the same.
This is a lot simpler than measuring the eyepiece focal length and focal length of a binocular. Although binoculars are sometimes described as two parallel refractors lashed together, these specifications just don't come in the box or on the binocular. Since my eyes tell me this adaptation works, I'm satisfied.
Link to Stellarium Plugin Bundle: Stellarium Plugins
Clear Skies and Season's Greetings!