CALCULATING EYEPIECE FIELD OF VIEWLast updated: 15 March 2004 |

Date: 3/12/04, 12:35 From: Dave Wallace (d_wallace@ecrm.com) The field of view may be calculated if you know (1) the focal length of the eyepiece in question, (2) the apparent field of view of the eyepiece in question, and (3) either the focal length of the telescope or the magnification provided by the eyepiece and telescope. For Meade eyepieces, you have data for items (1) and (2) -- see their product descriptions. Example: the 26 mm Series 4000 eyepiece has a focal length of 26 mm and an apparent field of view of 52 degrees. If you don't have the magnification OR the focal length but have the aperture and focal ratio, you can obtain the focal length (and the magnification) from that. Here are the formulae: V = Ve / m. (V is field of view; Ve is apparent FOV of eyepiece; m is magnification) m = F / Fe. (m is magnification; F is focal length of telescope; Fe is focal length of eyepiece) F = A * R. (A is aperture; R is focal ratio) So, depending on what you know, use either V = Ve / m or V = Ve * Fe / F or V = Ve * Fe / (A * R) Alternatively, measure the time it takes in minutes for a star at the celestial equator (DEC = 0) to go completely through the field of view when the telescope is not tracking. Call this T. Your field of view is then: V = 4 * T (V is in degrees and T is in minutes.) For more than you *ever* wanted to know about this, I have a freeware program available to calculate all this stuff. It's at http://wa1gsf.home.comcast.net/astronomy_blog.html#downloads (requires Windows operating system, unless you want to port from the source code)

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