How a digital sensor works

The lens in a camera focuses light on a plane behind the rear element

Typical Sensor Array in a Digital Cameraan array of light-sensitive spots, called photosites usually

square in shape and laid out in rows and columns

Sensor Architecture

Light-sensing portion of the photosite is called photo diode.

ELECTRONS = the “wild children” of the atom family

Photo DiodeWith some sensors the active light gathering area is as little as 25% of the total surface area of the chip. There is non-light responsive space between adjacent photo diodes.

Light to photosite in sensor

photo diode in photosite converts the light photons to electrons

Photosite stores electrons in the electron well buried in the photosite

NOISE . . . Hot pixels and lost data

Light to photosite in sensor

photo diode in photosite converts the light photons to electrons

Photosite stores electrons in the electron well buried in the photosite

Processor looks at blocks of this data and tries to guess the actual RGB color value of each pixel by comparing (demosaicing) it examines a block of adjacent pixels and uses that data to build the missing two values for each location. ( interpolation in mathematics, software routine that does this is more correctly called demosaicing.)

PROCESSING

Sensors are designed to operate like the human brain

Light to photosite in sensor

photo diode in photosite converts the light photons to electrons

Photosite stores electrons in the electron well buried in the photosite

“guess” the actual RGB color value of each pixel demosaicing

PROCESSING

RAW

Compression = pixels destroyed or eliminated by guessing actual color value

JPEG PROCESSING

JPEG

Depth of Field and Focal Length

DOF = depth of fieldFOV = Field of View

Bokeh

How much gear do you really need?

The longer the focal length, the creamier the bokehFocal Length: 600 mm (300mm lens with 2.0 teleconverter)

Iso 800F/8 at 1/80

Narrow depth of field isolates the subjectFocal Length: 300mm

Iso 400f/4 at 1/4000

Focal length: 280mmIso: 800

f/5.6 at 1/60

Focal Length: 60mm (macro)Iso: 200

f/8 at 1/200

Focal length: 18mmIso: 100

f/6.3 at 1/100

Focal Length: 24mmIso: 100

f/1.4 at 1/800

Focal Length: 85mmIso 100

f/1.8 at 1/200

Focal Length: 85mmIso 1600

f/1.8 at 1/125

Focal Length: 10mmIso 100

f/5 at 1/200

The “Holy Trinity” or the exposure Triangle

ISO (sensitivity to light)

Aperture (f-stop)Shutter Speed

Good combination = good photo