Digital Camera

Essential Elements

Part 1

Sept 13 2007

Basic Digital Camera

• Lens - usually with variable focal length to allow wide angle to telephoto view

• Shutter (either mechanical or electronic)• A view finder to compose the image• Sensor - an array of several million color filtered photo sensors,

or pixels (the Bayer array) converts light (photons) to electrons• An amplifier to modify sensor output• An analog to digital converter to digitize sensor output • A computer to convert the “raw” data to a visible image• A Liquid Crystal Display to view image• A data storage device – usually removable• A power source –standard batteries or custom rechargeable

battery

Bells & Whistles

• Automatic exposure• Automatic focus• Image stabilization (anti-shake)• Live view • Built in Flash • Movie mode• Adjustable image size & compression• RAW mode

Simple Camera

Compact Point and Shoot

Super Compact (Image Stabilized)

Super compact (folded optics)

Super Zoom

Hybrid

Traditional

4/3 format Digital SLR

APS format Digital SLR

Digital SLR Cross Section

Digital Camera ConceptsLens Focal Length

Focal Length Multiplier

Depth of Focus

Sensor Types

Bayer Array

Image Quality

Digital Noise

Dynamic Range

Lens Focal Length

• The lens focal length for digital cameras is usually stated in terms of “35mm equivalent” – a carry-over from the most popular film format– The true focal length is much shorter because

most digital camera sensors are much smaller than the 35 mm film frame

– Normal zoom range is 3X to 4X– Super zoom ranges from 12X to 15X

Focal Length Multiplier (FLM)

• FLM is equal to the diagonal (43.3mm) in the 35mm film frame divided by the diagonal of the digital sensor. – The concept is important on a digital

SLR when older 35mm film camera lenses are attached.

Depth of Focus / Depth of Field

• Depth of Focus is the distance on either side of image plane where focus is “acceptable”

– “Acceptable” is defined by the Circle of Confusion “d”– “d” is approximately: Sensor Diagonal(mm) / 1500

• Depth of Field is the distance in front and back of the object plane that will yield acceptable focus. When a lens focuses on a subject at a distance, all subjects at that distance are sharply focused. Subjects that are not at the same distance are out of focus and theoretically are not sharp. However, since human eyes cannot distinguish very small degree of unsharpness, some subjects that are in front of and behind the sharply focused subjects can still appear sharp.

• We can use smaller apertures for increasing the depth of field – at some cost in terms of maximum sharpness of focus

DOF Concept

Lens Summary

• Consumer digital cameras are fitted with lenses with short focal lengths to create 35mm equivalent field of views on their small sensor surfaces.

• Because of the shorter focal length lens used, DOF, the depth of field, is much more than 35mm film cameras with the same field of view. – This allows for economical automatic focus on digital cameras

 

• Example: Sensor diagonal = 1/4 of 35 mm frame, lens set to 8mm focal length, F/4 aperture. DOF is equivalent to a 35 mm camera with 32 mm lens stopped down to F/16

The Sensor

CCD / CMOS are common types– CCD (Charge Coupled Device)– CMOS (photo transistor with “on pixel”

electronics)

CCD Sensor

CCD Cross Section

CMOS Sensor Array

(2) Sensor Cont’d

RBG Bayer Array

A pattern of pixels with alternating R G B G filters that enable a computer to “synthesize” color. (The sensor has no color sensitivity)

Bayer Layout

Bayer Filter Array

Bayer Interpolation

(3) Sensor Continued

Sensor Array Size – seldom expressed in simple terms

Common Sensor Sizes (Approximate)Type W : H Diagonal mm Width mm Height mm

Full Frame (35mm)

3:2 43.3 36 24

APS 7:5 or 3:2 28.8 23.4 16.7

“4/3 in.” 4:3 22.5 18 13.5

“1 in.” 4:3 16 12.8 9.6

“2/3 in.” 4:3 11 8.8 6.6

“1/1.8 in.” 4:3 8.9 7.2 5.3

“1/2.5 in.” 4:3 6.4 3.8 5.1

“1/3.6 in.” 4:3 5.0 4.0 3.0

(4) Sensor Cont’d

Megapixels –Marketing emphasis because it’s simple, has “some” relevance and plays to conditioned response – “Bigger is Better”

Physical Size – never expressed clearly

The important dimensions are pixel “pitch” and number of active pixels

Pitch defines the area of a pixel – thus it’s light gathering ability

Number of pixels relates to fine detail resolution