I would like to know the field of view I can archieve with my scope if I am going to buy an eyepiece, especially a wide angle eyepiece. Apply the formula below, you can get a rough figure of the true field of view (TFOV). Why is it just a rough figure? There are still several factors to be taken account but I think this is good enough. There is a more precise formula to do the same work.
TFOV = AFOV of Eyepiece / Magnification
The apparent FOV (AFOV) of an eyepiece is provided by the manufacturer. To know the magnification, please refer to Calculate Eyepiece Magnification.
Apparent Field of View of Several Eyepiece Designs
Orthoscopic – 43º
Plossl – 50º
Radian – 60º
Panaoptic – 68º
Nagler – 82º
If you know the True Field of View of an Eyepiece and the Angular size of a body how do you calculate the size of the body in the True Field of View?
(% of the Angular Diameter of the True Field of View filled by the body)
Interesting question. Does the angular size of the object computed without any optical aid (without using telescope)?
The method that I just figured out is to calculate the angular size of the body shown in the eyepiece and then divide the TFOV of the eyepiece by the angular size of that object. Afterthat, you time the result 100%, then you know the answer.