Question

A small refracting telescope designed for individual use has an objective lens with a diameter of 6.00 cm and a focal length of 1.325 m. what is the f-number of this instrument?

Answer 1

The f-number of the telescope is calculated by dividing the focal length (1.325 m) by the diameter of the lens (6.00 cm), resulting in an f-number of approximately 22.08.

Step-by-step explanation:

The f-number of a telescope's objective lens is calculated by dividing the focal length by the diameter of the lens. In this case, the objective lens has a focal length of 1.325 m (which is 1325 mm since 1 m = 1000 mm) and a diameter of 6.00 cm (which is 60 mm since 1 cm = 10 mm). Using the given values, the f-number, often represented as f/# or f-stop, is calculated as:

f/# = focal length / diameter of the lens

f/# = 1325 mm / 60 mm

f/# = 22.08

Therefore, the f-number of this refracting telescope is approximately 22.08.

Answer 2

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