RBG three different sensors
Fish 2 ft away appears 3ft away in water
Chromatic aberration, each color bends differently. Solution : Achromatic lenses, two lenses that cancel each other effect.
Bigger lens to gather more light to focus on sensor.
AF:
1. Active: smaller cameras, IR based, good at night, works for small distances only
2. Passive: Old DSLRs have linear sensor, tries to have max delta in intensity of adj photodiodes
USM:
Ultrasonic motors.
Piezoelectric effect.
DSLRs AF uses EYE! IR LED reflects IR from retina and sensor using its metering zones that have AF points, tries to determine where eye is looking.
That's why there is a diopter corrector in viewfinder.
Viewfinder:
Normal : they have parallax, hence have parallax indicator
DSLRs: through the lens (TTL) viewfinder (have mirror), accurate
EVFs: Electronic VFs: quieter (no mirror) but drain battery.
Lens:
Normal: Focal length = diagonal length of img sensor
Wide angel : FL < diag of img sensor , fisheye < 15mm (180 deg) converging/positive
Telephoto: > 65mm , diverging/negative