The telescope: Magnifying power
 

Direct the telescope to the day sky and place a thin piece of paper over the eyepiece. Measure the diameter of the exit pupil, d, for a range of values of the entrance aperture, D. From a plot of d against D, determine the gradient. The magnifying power is defined by the ratio D/d and, hence, the measured gradient provides a value for the magnifying power of the telescope and eyepiece combination.
Change the eyepiece for one with a different focal length and repeat the experiment.