Samsung Galaxy NX500 Camera User Manual (en)

Concepts in Photography
Correlation between focal length, angle, 
and perspective
Focal length, which is measured in millimeters, is the distance between 
the middle of the lens to its focal point. It affects the angle and perspective 
of captured images. A short focal length translates into a wide angle, 
which allows you to capture a wide shot. A long focal length translates 
into a narrow angle, which allows you to capture telephoto shots.
Short focal length
wide shot
wide angle
wide-angle lens
Long focal length
telephoto shot
narrow angle
telephoto lens
Look at these photos below and compare the changes.
16 mm angle
50 mm angle
200 mm angle
Normally, a lens with a wide angle is suitable for shooting landscapes and a lens 
with a narrow angle is recommended for shooting sports events or portraits.