June 2005
Beginner
412 pages
13h 45m
English
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Determine Your True Field of View
A drift test lets you figure out just how much of the sky you can keep in your sights.
Any combination of telescope and eyepiece has a specific true field of view (TFoV), which is determined solely by the focal length of the telescope and the field stop diameter of the eyepiece. TFoV quantifies the amount of sky visible in a particular scope with a particular eyepiece. For example, if a particular telescope/eyepiece combination provides a 1° TFoV, two stars that are separated by exactly 1° will just fit into the eyepiece field, with each star on opposite edges of the field.
It is important to know the TFoV of your eyepieces in your scope and the TFoV of your finder because you use the true field to match the stars that are visible in the eyepiece to those on your charts and to plan and execute star hops [Hack #21]. There are several methods, of varying accuracy, to determine TFoV.
- The Apparent Field of View (AFoV) method
The quickest way to determine TFoV is to divide the Apparent Field of View (AFoV) of the eyepiece by the magnification provided by that eyepiece in a given scope. For example, if your scope has a focal length of 1,200mm and you use a 25mm Plössl eyepiece with an AFoV of 50°, you can calculate the TFoV as follows:
Divide the focal length of the scope, 1,200mm, by the focal length of the eyepiece, 25mm, to determine that that combination provides 48X magnification.
Divide the AFoV, 50°, by the magnification, 48X, to yield a TFoV of 50/48, ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.