Comments on: How do I determine my Telescope’s Focal Length? http://www.telescopebuyingguide.com/blog/how-do-i-determine-my-telescopes-focal-length/ Thu, 17 May 2012 20:12:55 +0000 http://wordpress.org/?v=2.7 hourly 1 By: cosmo http://www.telescopebuyingguide.com/blog/how-do-i-determine-my-telescopes-focal-length/comment-page-1/#comment-1744 cosmo Tue, 28 Jul 2009 20:05:45 +0000 http://www.telescopebuyingguide.com/blog/how-do-i-determine-my-telescopes-focal-length/#comment-1744 If it's a Cassagrain, the focal length is much longer than the length of the tube. 1) Look up the model on the manufacturer's website. 2) get a reticle calibrated in, e.g. millmeters, put it at the focus between telescope and eyepiece, and measure a planet or a double star with known angular diameter. The focal length is the size of the object in millimeters, divided by its angular extent in radians. If it’s a Cassagrain, the focal length is much longer than the length of the tube.

1) Look up the model on the manufacturer’s website.

2) get a reticle calibrated in, e.g. millmeters, put it at the focus between telescope and eyepiece, and measure a planet or a double star with known angular diameter. The focal length is the size of the object in millimeters, divided by its angular extent in radians.

]]> By: Doc89891 http://www.telescopebuyingguide.com/blog/how-do-i-determine-my-telescopes-focal-length/comment-page-1/#comment-1743 Doc89891 Mon, 27 Jul 2009 04:05:54 +0000 http://www.telescopebuyingguide.com/blog/how-do-i-determine-my-telescopes-focal-length/#comment-1743 Its usually stamped or printed on the tube or focuser somewhere. probably some number between 800 and 1200 Measure from the objective to the eyepiece with a tape and convert that to mm. There should be a number somewhere that corresponds, roughly, to your measured number Its usually stamped or printed on the tube or focuser somewhere. probably some number between 800 and 1200

Measure from the objective to the eyepiece with a tape and convert that to mm. There should be a number somewhere that corresponds, roughly, to your measured number

]]> By: Tina L http://www.telescopebuyingguide.com/blog/how-do-i-determine-my-telescopes-focal-length/comment-page-1/#comment-1742 Tina L Fri, 24 Jul 2009 19:48:26 +0000 http://www.telescopebuyingguide.com/blog/how-do-i-determine-my-telescopes-focal-length/#comment-1742 doesn't it say on it? unless it's a mak or sct, you can measure it from first principles with a tape measure. doesn’t it say on it?

unless it’s a mak or sct, you can measure it from first principles with a tape measure.

]]>