# How to compute the Exit pupil size of a telescope?

## Computing Exit Pupil Size of an optical system¶

### The NA is simply the ratio of the diameter of the aperture over the focal length¶

$$NA (rad) = \frac{D}{f}$$

### Dividing the maximum frequency by the sampling size yields to:¶

$$\frac{D\times \Delta x \times N }{2\times f}$$