aperture

noun
1
a small opening in something
روزنه, دهانه, سوراخ, شکاف
2
an opening that allows light to reach a lens, especially in cameras
دهانه, روزنه, دیافراگم
For flash photography, set the aperture at f. 5.6.
Open up the lens aperture to maximize the brightness of the shot.
Binoculars of this aperture are very expensive.