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Magnification of unknown ep


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In response to Chris's (Lunatic) query in the shoutbox.

Measure the exit pupil of your home made eyepiece.

To do this, roughly point your scope at a bright window or sky in daylight - NOT THE SUN.

Look into the eyepiece from a few inches away and you will see a bright disc of light which will normally be somewhere between 1mm and 6mm across.

Use a ruler and accurately measure the diameter of this disc. This is the exit pupil.

Divide the aperture in mm of your scope by the exit pupil to get the magnification.

If you want to know the focal length of the eyepiece then divide the telescope focal length (700mm in Chris's case) by the magnification that you have just found.

Double check your calculations 'cos it is very easy to make a simple mistake and get totally wrong answers.

Hope this helps.


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