The three pillars of exposure

F2.8

F16

1.) The pupil is what we refer to the aperture.

2.) small pupil side equals small aperture

3.)The size of the aperture has a direct impact on the depth of field 

wich is the are of the image that appears sharp. a large f- number such as 

f/32 ( with means a smaller aperture) will bring all foreground and background objects in focus.

#1

f.) the diamonds performance i would take it at a fast shutter speed to 

get a good picture of the moves.

e.0 the DJ/MC working at the middle of the circle 

where you could see all the lights.

#2.) when the camera is in auto mode,both shutter and aperture are automatically selected 

by the camera 

aperture priority mode , you set the lens aperture , while the camera auto magically sets to shutter speed.

shutter priority mode where you set the both shutter speed and the camera

automatically selects the aperture.