You look at Vega, a star of apparent magnitude m=0,
with a telescope of diameter d = 6 inches = 15 cm.
How many photons enter the telescope each second?

        Each second, one million photons per second
        from Vega pass through an area of 1 sq. cm.
        We need to find the area of this telescope:

            diameter = 15 cm

            radius   =  7.5 cm

            area     =  pi*radius^2  =  177 sq.cm.

        Therefore, 

            flux    =   (1,000,000 photons/sec/sq.cm) * (177 sq.cm.)

                       177,000,000 photons/sec     into telescope


        That's a lot of photons!