If you want the portrait to make the subject look good, the focal length matters.
Focal length-the focal length of a lens is defined as the distance in mm from the optical center of the lens to the focal point (the sensor) when the lens is focused on infinity.
Focal length controls: Magnification and angle of view
Focal length is described as short, normal-close to human vision, or long.
A wide angle lens or short lens is 35 mm or less.
A normal lens is 35 mm to 70mm. The “focal length” of the human eye is about 50mm.
A medium telephoto lens is 70-135. A telephoto lens or long lens is 135-300+.
Generally, 80-100 is a good focal length range for complimentary portraits.
Shooting a portrait at a wide angle lens will distort your model’s features. All cameraphones have a fixed wide angle focal length (unless you have the iPhone 11 with multiple lenses.)
Watch this video to see the effect of different focal lengths on a portrait.
Technical Note
