# Angular Resolution of a Telescope

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• #574827
Michael E. Marotta
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Angular resolution in radians = 1.22 times the quotient (wavelength / aperture)

Make sure to keep the units the same, wavelength may be in angstroms; aperture may in inches. So, do the conversions first.

For example, a telescope with a 10-inch lens is assumed to be observing in the visible spectrum. Assume the middle range. The last step is to convert radians to arc seconds.

My telescope has an aperture of 102 mm.

Answer ranges 0.98″ (violet) to 1.72″ (red)

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#583553
Michael E. Marotta
Participant

The example comes from  A Student’s Guide to the Mathematics of Astronomy by Fleisch & Kregenow, Cambridge University Press, 2013.

#583554
Dr Paul Leyland
Participant

You give the accurate (and correct) procedure.  For a decent approximation I just divide 140 by the aperture in mm, which gives an answer which is “good enough”.  In your case 140/102 = 1.37.

Easy to remember.

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