F-number is 2.21
The f-number is defined as the ratio of the focal length to the diameter of the entrance pupil. So the equation is
N = f/D
where
N = f-number
f = focal length
D = entrance pupil
With the telescope, the entrance pupil will be assumed to be equal to the lens diameter. So substituting the known values into the equation.
N = 1.325 m / 0.0600 m
N = 2.208333333
Rounding to 3 significant figures gives a F-number of 2.21
