Determining resolving power of telescope

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The telescope is employed to view distant objects and therefore the amount of gain which it reveals depends on the angle where the two point objects subtend at the objective rather on linear separation between them.The resolving power of a telescope is therefore defined as the inverse of the least angle subtended at the objective by by two distant point objects which can be just distinguished as separate in its focal plane.


Focus the telescope of the spectrometer for receiving parallel light. Set the illuminated gauze at a distance of about 5m from the objective of the telescope, and place the adjustable vertical slit immediately in front of the objective.Open the slit as wide as possible.Observe the gauze through the telescope and bring it clearly into focus by adjustment of the eye piece. Now slowly reduce the width of adjustable slit until the vertical wires of the gauze can no longer be seen as separate wires but appear to have fused into a single indistinct blurred image.Make the fine adjustments to the width of the slit by first opening it farther and then contracting it until the critical width of the slit has been obtained for which the vertical wires of the gauze can just, but only just, be discerned as separate and distinct wires. The wires are then said to be just resolved.

1.separation of vertical wires (a) are measured by means of travelling microscope 2.meter ruler helps in measuring the distance between gauze and adjustable slit(d) 3.resolving power = mean value of a/mean value of d

Theory shows that for a rectangular aperture

      resolving power= wavelength of light/width of aperture(D)




  1. rie procedure 7 sem