27-03-2012

Workshop One - Location       27-03-12

Belinda Pratten                          Week Seven                                  Semester One

·         Digital Capture Continued

·         Does size matter – Sensor Array

·           yes and no

·           larger size = more photosites = more resolution

·           smaller size = more compact = cheaper

·         35mm film (35mm wide)

·           image area = 24mm x 36mm

·           half frame compact cameras = 18mm x 24mm (circa 1913)

·         35 =  50mm lens is ‘normal’ for this format

·         35 =  75mm lens ‘crops’ the image with narrower angle of view

·         Crop factor

·           full frame sensor = 24mm x 36mm (same as film)

·           smaller sensors defined against this standard with a ‘crop factor’

·           ‘crop factor’ refers to cropping of lens angle of view due to smaller
   sensor size.

·         Quick calculation of crop factor

·         crop factor =     full frame dimension / smaller sensor dimension

·         crop factor = 36mm/23.6mm=  1.5x

·         Use crop factor to calculate new effective lens focal length

·         5”x7” longest side = 178mm

·         35mm longest side = 36mm

·         178mm/   36mm = 4.9x

·         Crop factor:  4.9x

·         Lens focal length = 210mm

·         Effective focal length =

·         210 x 4.9x = 1029mm

Full frame	1.3x	1.5x	1.6x
10mm	13mm	15mm	16mm
17mm	22.1mm	25.5mm	27.2mm
28mm	36.4mm	42mm	44.8mm
50mm	65mm	75mm	80mm
105mm	136.5mm	157.5mm	168mm
135mm	175.5mm	202.5mm	216mm
200mm	260mm	300mm	320mm

·         Lenses designed for the smaller sensor should not be used
   with a full-frame sensor

·         Why?

·         The sensor array is made up of millions of photosites;

·           range in size from 1.7µm - 8.4 µm  (also referred to as pixel pitch)
   µm =                                                                                                                       micrometer (1/millionth of a metre or 1/thousandth of a mm)

·         For a given sensor array

·         large photosites = less in a given area 

·           small photosites = more in a given area

	Large sites	Small sites
Given sensor area	Fewer	Greater number
Resolution	Lower	Higher
Light gathering ability	Higher	Lower
Signal strength	Higher	Lower
Blooming	Slower to bloom	Quicker to bloom
Sensor Dynamic Range	Higher	Lower
Level of noise	Lower	Higher

·         What is digital noise?

·         analogous to crackle in audio system / hiss in radio signal

·           all electronic devices create unwanted electronic ‘noise’

·           digital sensor collects photons and creates a signal in
   proportion to amount of photons collected and…

·           unavoidably creates a level of electronic ‘noise’

·           HIGH ISO = signal is weaker, noise is constant,
   amplification raises both levels so ratio of noise to signal is greater.

·           high temperatures or long exposures may also increase noise level

·         Fixed Pattern

·         Long exposure

·         Low ISO

·         Higher temperature

·         (hot pixels)

·         Random

·         Short exposure

·         High ISO

·         Banding

·         Camera dependent

·         High ISO

·         In shadows

·         Heavily lightened image

·           if ‘noise’ is a constant then a smaller site will have a higher
   Noise to Signal ratio,

·          -  image quality is affected

·          -  ISO is affected….?

·         High level of noise may cause blooming to happen

·         Photosite size and blooming

·         small photosite fills

·           may spill into adjacent site

·           this is known as ‘blooming’

·           high noise level may cause this to happen as well

·        

·          Dynamic Range is the ability of sensor to record low through to high luminances

·           SLR = subject luminance range

·           Film:  known as ‘density range’

·           if photosite overflows it is called ‘blooming’

		f-stops	Ratio
High contrast scene		11 stops	2
Low contrast scene		6 stops	64:1
Human eye full working range		15 stops	32,000:1
Human eye (fixed on one part of scene)		6 stops	64:1
B&W negative film		11 stops	2048:1
Colour positive film		7 stops	128:1
DSLR low ISO		9 stops	512:1
DSLR high ISO		7 stops	128:1
Glossy photo paper		7-8 stops	128/256:1
	Bit Depth
	* Bit depth specifies how much colour information is available for each pixel in an image.   * The more bits of information per pixel, the more available colours and more accurate colour      representation.      For example, an image with a bit depth of 1 has pixels with two possible values: black and white. An      image with a bit depth of 8 has 28, or 256, possible values. Grayscale mode images with a bit depth of      8 have 256 possible gray values.   * RGB images are made of three colour channels. An 8‑bit per pixel RGB image has 256 possible values     for each channel which means it has over 16 million possible colour values. RGB images with 8‑bits per     channel (bpc) are sometimes called 24‑bit images (8 bits x 3 channels = 24 bits of data for each pixel).     http://help.adobe.com/en_US/photoshop/cs/using/WSfd1234e1c4b69f30ea53e41001031ab64-73daa.html

·         1 bit depth = 2 values

·         2 bit depth = 4 values

·         3 bit depth = 8 values

·         RGB capture

·          bit depth per channel, ie 3 channels, RGB

·          bit depth per channel is typical camera rating;

·         eg. 12 bit capture (per channel)

Philip Bloom Clanging and Banging the redneck hippie