How do I determine my Telescope’s Focal Length?
nymets6159 asked:
Well I really don’t exactly know what telescope I have, I know it’s a Meade telescope, but I don’t know the model. But, anyways, how would I find out the telescope’s focal length? Please I need this to check my eyepiece magnifications.
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Well I really don’t exactly know what telescope I have, I know it’s a Meade telescope, but I don’t know the model. But, anyways, how would I find out the telescope’s focal length? Please I need this to check my eyepiece magnifications.
July 24th, 2009 at 2:48 pm
doesn’t it say on it?
unless it’s a mak or sct, you can measure it from first principles with a tape measure.
July 26th, 2009 at 11:05 pm
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
July 28th, 2009 at 3:05 pm
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.