Digital Camera Essential Elements Part 1 Sept

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 Concepts Lens 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) TypeW : HDiagonal mmWidth mmHeight mm Full Frame (35mm) 3: APS7:5 or 3: “4/3 in.”4: “1 in.”4: “2/3 in.”4: “1/1.8 in.”4: “1/2.5 in.”4: “1/3.6 in.”4:

(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