4.light n color

Light and Color

Red Eye

2

24 Chapter 1 How Digital Cameras Capture Images

There are a few ways to minimize or eliminate red-eye in your pictures. Some cameras provide a red-eye reduction feature that fires a preflash, forcing the irises in your subject’s eyes to close before you take the picture. The main problem with this method is that it often forces subjects to involuntarily close their eyes before the image is taken, and it doesn’t always completely eliminate the red-eye effect.

A more effective method is to use an external flash via the camera’s hot-shoe mount or, better yet, with an extension bracket. An external flash radically changes the angle of the flash, preventing the lens from capturing the reflection of the blood in the back of your subject’s eyes.

While you can also fix the red-eye effect using Aperture, there is no way to accurately reproduce the original color of your subject’s eyes. Preventing the problem before it occurs is the preferred solution.

Light enters the eye and bounces straight back into

the camera, causing the red-eye effect.

Built-in flash

External flash unit Light enters the eye at different angles, diffusing

as it leaves the eye.

LIGHTING: Bigger light source

26 Light: how images form

the limit of response is reached at 700 nm. So the colours of thespectrum – violet, blue, green, yellow and red – are really all present indifferent kinds of white light (sunlight, flash or studio lamps forexample).

The human eye seems to contain three kinds of light receptors,responding to broad overlapping bands of blue, green and redwavelengths. When all three receptors are stimulated equally bysomething you see, you tend to experience it as white, or neutral grey.If there is a great imbalance of wavelengths – perhaps the light containsfar more red (long) waves than blue (short) waves – stimulus is uneven.Light in this case may look orange tinted, just as happens every dayaround sunrise or sunset.

Try to remember the sequence of colours of the visible spectrum. It’suseful when you need to understand the response to colours of blackand white films, or choose colour filters and darkroom safelights (seeChapter 12). Later you will see how the concept of three human visualreceptors together responding to the full colour spectrum is adapted tomake photographic colour films work too.

It seems odd that humans can biologically sense only a relatively tinypart of the vast electromagnetic spectrum. However, with mostnaturally occurring infra-red, ultra-violet, X-ray and gamma-raywavelengths from space shielded from us by the Earth’s atmosphere,we have evolved without need of detection devices (or defences) forthese kinds of radiation. Beings on another planet, with a totallydifferent environment, might well have evolved with organs capable ofsensing, say, radio waves but completely ‘blind’ to visible light as weknow it.

Shadows

Light travels in straight lines and in all directions from a light source.This means that if you have direct light from a comparatively ‘compact’source such as the sun in a clear sky, a candle, bare light bulb or a smallflash unit, this light is harsh. Objects throw contrasty, sharp-edgedshadows. Figure 2.5 shows how having all the light issuing from onespot must give a sudden and complete shut-off of illumination at the

Figure 2.5 A compact, distant lightsource used direct makes objectscast a sharply defined shadow. Alarger source – simply formedhere by inserting a large sheet oftracing paper – gives a soft,graduated shadow. See alsoFigure 7.1

LIGHTING: Bounced light sca=ers When light reaches a surface 27

shadow edge. But look what happens when you place tracing paper inthe light beam (or block the direct light and reflect the remainder off amatt white wall, Figure 2.6). Tracing paper passes light but also diffusesit. The light passed through the paper scatters into new straight linesproceeding in all directions from every part of its large area surface.The object you were illuminating now casts a softer-edged, graduatedshadow, and the larger and closer your diffusing material the less harshand contrasty the shadow becomes. This is because light from a largearea cannot be completely blocked out by the subject; most of the partspreviously in shadow now receive at least some illumination. The samewould happen with sunlight on an overcast day.

It’s very important in practical photography to recognize thedifference between direct, harsh lighting and soft, diffused lighting.Shadow qualities greatly influence the way subjects and scenes look.Bear in mind this is not something you can alter in a photograph bysome change of camera setting or later manipulation. Understandingand controlling lighting is discussed in detail in Chapter 7.

When light reaches a surface

When light strikes a surface – maybe a building, or a landscape or face– what happens next depends upon the texture, tone and colour of thematerial, and the angle and colour content of the light itself.

Materials opaque to light

If the material is completely opaque to light – metal or brick forexample – some light is reflected and some absorbed (turned into heat).The darker the material the smaller the proportion of light reflected.This is why a dark camera case left out in the sun gets warmer than ashiny metal one.

If the material is also coloured it reflects wavelengths of this colourand absorbs most of the other wavelengths present in the light. Forexample blue paint reflects blue, and absorbs red and green from whitelight. But if your light is already lacking some wavelengths this willalter subject appearance. To take an extreme case, when lit by deep redillumination, a rich blue will look and photograph black, see Figure 2.7.You need to know about such effects in order to use colour filters(Chapter 9).

Surface finish also greatly affects the way light is reflected. A mattsurface such as an eggshell, drawing paper or dry skin scatters the lightevenly. The angle from which light strikes it makes very littledifference. However, if the surface is smooth and reflective it acts morelike a mirror, and reflects almost all the light back in one direction. Thisis called specular reflection.

If your light strikes the shiny surface at right angles it is reflectedbackward along its original path. You get a patch of glare, for example,when flash-on-camera shots are taken flat on towards a polished glasswindow or gloss-painted wall. But if the light is angled it reflects offsuch surfaces at the same angle from which it arrived, Figure 2.7. So tryto arrange your lighting direction or camera viewpoint to bounce glarelight away when photographing a highly reflective surface. (If you areusing built-in flash angle your camera viewpoint.)

Figure 2.6 A lamp, sunlight orflashgun directed entirely onto amatt white surface such as a wallor large card will reflect to alsogive soft, diffused shadows

LIGHTING: How color is made?

Wavelengths and colours 25

1 Light behaves as if it moves in waves, like ripples crossing thesurface of water, Figure 2.2. Different wavelengths give our eyes thesensation of different colours.

2 Light travels in a straight line (within a uniform substance). You cansee this in light ‘beams’ and ‘shafts’ of sunlight, Figure 2.1, and theway that shadows fall.

3 Light moves at great speed (300,000 kilometres or 186,000 miles persecond through space). It moves less fast in air, and slightly slowerstill in denser substances such as water or glass.

4 Light also behaves as if it consists of energy particles or ‘photons’.These bleach dyes, cause chemical changes in films and electronicresponse in digital camera sensors, etc. The more intense the light,the more photons it contains.

Wavelengths and colours

What you recognize as light is just part of an enormous range of‘electromagnetic radiations’. As shown left, this includes radio waveswith wavelengths of hundreds of metres through to gamma and cosmicrays with wavelengths of less than ten thousand-millionths of amillimetre. Each band of electromagnetic radiation merges into thenext, but has its own special characteristics. Some, such as radio, can betransmitted over vast distances. Others, such as X-rays, will penetratethick steel, or destroy human tissue. Most of this radiation cannot be‘seen’ directly by the human eye, however. Your eyes are only sensitiveto a narrow band between wavelengths 400 nm and 700 nm approx-imately. (A nanometre or nm is one millionth of a millimetre.) Thislimited span of wavelengths is therefore known as the visiblespectrum.

When a relatively even mixture of all the visible wavelengths isproduced by a light source the illumination looks ‘white’ andcolourless. But if only some wavelengths are present the light appearscoloured. For example, in Figure 2.3, wavelengths between about400 nm and 450 nm are seen as dark purpley violet. This alters to blueif wavelengths are changed to 450–500 nm. Between 500 nm and580 nm the light looks more blue-green, and from about 580 nm to600 nm you see yellow. The yellow grows more orange if the lightwavelengths become longer; at 650 nm it looks red, becoming darker as

Figure 2.2 Light travels on astraight line path but as if inwaves, like the outwardmovement of ripples when asmooth water surface is disturbed

Figure 2.3 Some of theelectromagnetic spectrum (left),and the small part of it formingthe visible spectrum of light(enlarged, right). Mixed in roughlythe proportions shown in colourhere, the light appears ‘white’

Figure 2.4 Most sources of lightproduce a mixture ofwavelengths, differing in colourand expressed here in greatlysimplified form

Wavelengths and colours 25

1 Light behaves as if it moves in waves, like ripples crossing thesurface of water, Figure 2.2. Different wavelengths give our eyes thesensation of different colours.

2 Light travels in a straight line (within a uniform substance). You cansee this in light ‘beams’ and ‘shafts’ of sunlight, Figure 2.1, and theway that shadows fall.

3 Light moves at great speed (300,000 kilometres or 186,000 miles persecond through space). It moves less fast in air, and slightly slowerstill in denser substances such as water or glass.

4 Light also behaves as if it consists of energy particles or ‘photons’.These bleach dyes, cause chemical changes in films and electronicresponse in digital camera sensors, etc. The more intense the light,the more photons it contains.

Wavelengths and colours

What you recognize as light is just part of an enormous range of‘electromagnetic radiations’. As shown left, this includes radio waveswith wavelengths of hundreds of metres through to gamma and cosmicrays with wavelengths of less than ten thousand-millionths of amillimetre. Each band of electromagnetic radiation merges into thenext, but has its own special characteristics. Some, such as radio, can betransmitted over vast distances. Others, such as X-rays, will penetratethick steel, or destroy human tissue. Most of this radiation cannot be‘seen’ directly by the human eye, however. Your eyes are only sensitiveto a narrow band between wavelengths 400 nm and 700 nm approx-imately. (A nanometre or nm is one millionth of a millimetre.) Thislimited span of wavelengths is therefore known as the visiblespectrum.

When a relatively even mixture of all the visible wavelengths isproduced by a light source the illumination looks ‘white’ andcolourless. But if only some wavelengths are present the light appearscoloured. For example, in Figure 2.3, wavelengths between about400 nm and 450 nm are seen as dark purpley violet. This alters to blueif wavelengths are changed to 450–500 nm. Between 500 nm and580 nm the light looks more blue-green, and from about 580 nm to600 nm you see yellow. The yellow grows more orange if the lightwavelengths become longer; at 650 nm it looks red, becoming darker as

Figure 2.2 Light travels on astraight line path but as if inwaves, like the outwardmovement of ripples when asmooth water surface is disturbed

Figure 2.3 Some of theelectromagnetic spectrum (left),and the small part of it formingthe visible spectrum of light(enlarged, right). Mixed in roughlythe proportions shown in colourhere, the light appears ‘white’

Figure 2.4 Most sources of lightproduce a mixture ofwavelengths, differing in colourand expressed here in greatlysimplified form

LIGHTING: When light reaches 28 Light: how images form

Materials transparent or translucent to light

Not every material is opaque to light, of course. Clear glass, plastic andwater for example are transparent and transmit light directly, whiletracing paper, cloud and ground glass diffuse the light they transmit andare called translucent. In both cases if the material is coloured it willpass more light of these wavelengths than other kinds. Deep red stainedglass transmits red wavelengths but may be almost opaque to blue light,see Figure 2.8.

Since translucent materials scatter illumination they seem milkywhen held up to the light and look much more evenly illuminated thanclearer materials, even when the light source is not lined up directlybehind. Slide viewers work on this principle. The quality of the light issimilar to that reflected from a white diffused surface.

Refraction

Interesting things happen when direct light passes obliquely from airinto some other transparent material. As was said earlier, light travelsslightly slower when passing through a denser medium. When lightpasses at an angle from air into glass, for example, its wavefront(remember the ripples on the water, Figure 2.2) becomes slowedunevenly. This is because one part reaches the denser material first andskews the light direction, like drawing a car at an angle into sand,Figure 2.9. A new straight-line path forms, slightly steeper into theglass (more perpendicular to its surface). The change of light path whenlight travels obliquely from one transparent medium into another isknown as refraction.

Figure 2.7 Light reflection. Top:Light reflected from a mattsurface scatters relatively evenly.Centre: From a shiny surface lightat 90º is returned direct. Obliquelight directly reflects off at thesame angle as it arrived(incident). Bottom: Colouredmaterials selectively reflect andabsorb different wavelengthsfrom white light. However,appearance changes when theviewing light is coloured

UNDERSTANDING HISTOGRAMS

A high-‐contrast image produces a histogram in which the tones are spread out.

This image has fairly normal contrast, even though there are no true blacks showing in the histogram.

This low-‐contrast image has all the tones squished into one end of the grayscale.

UNDERSTANDING HISTOGRAMS

An underexposed image will look like this

Histogram of an overexposed image will show clipping at the right side

Increasing exposure will produce a histogram like this

Shu=er

Shawn Peterson, Bodie, Wheel of Wonder, California, 2008 23, 4 min exposures sWtched together

M

oonlight and Star Trails 211

any gaps in the star trails that appear during the time it takes to refocus. If there is nothing of importance in your foreground, perhaps only the horizon, focus at infinity and use the aperture setting one stop down from maximum. You should check the foreground focus using live view and a flashlight, with the lens stopped down to your shooting aperture. Live view can also be used to focus at infinity on the stars and to assist in composing the shot by establishing the four corners of the image. You may wish to do high-ISO test shots to help you establish the composition and position the foreground elements and stars in relation to one another. However, it is a good idea to do a full-length exposure to test the direction of star trail movement in your shot. The stars will not move enough during a high-ISO shot to clearly establish the pattern and direction of movement.

If you plan to do any light painting in the foreground, you should test the lighting at your working ISO to determine the best way to illuminate the shot and how much light is needed. Because you’ll be investing a long period of time in this procedure, you’ll want to make sure everything is perfect.

Shawn Peterson, “Bodie Wheel of Wonder,” Bodie, California, 2008

This giant wheel was part of the mining operation at Bodie State Historic Park in California. Shawn Peterson and Scott Martin worked together to carefully compose this image, taking time to position the star trails so that they would mirror the shape of the wheel. The wheel itself was lit with a flashlight during the first and last of 23 4-minute exposures, which were processed in Lightroom and then stacked with Startrails, a Windows-based shareware program.

Light PainWng

Cenci Goepel & James Warnecke, 2007 Somewhere in ArgenWna

234

NIG

HT

PH

OT

OG

RA

PH

Y

Cenci Goepel and Jens Warnecke, “Lightmark No. 54 | S 50°24’40.1” W 72°42’04.7”, Provincia de Santa Cruz, Argentina,” 2007

In this photo, we spun a band with an LED flashlight only on a single plane. The spiral shape is a result of the gradual shortening of the band as it spins. To achieve the space between the outer and inner rings of the spiral, we took a break by covering the lens briefly during the exposure.

Light PainWng

Light Painting

233

Cenci Goepel and Jens Warnecke, “Lightmark No. 63 | N 61°39’51.9” E 6°51’27.8”, Briksdalsbreen, Norway,” 2007

It took a 3-hour uphill hike on a frozen path to reach the foot of the glacier and 3 nights to create this photograph. From below, it was impossible to tell what the weather would be like above. The first 2 nights were so bad that we couldn’t photograph a single thing, but it was a beautiful hike nonetheless! The third night was a charm—perfectly clear, as you see here. The ball was created by spinning an LED flashlight attached to a band in a circle as well as around the painter’s own axis.

Cenci Goepel & James Warnecke, 2007 Somewhere in Norway

Reciprocity 28_29

=

Reciprocal relationships

Once the reciprocal relationship

between f-stop and shutter speed

is established combinations of

f-stop and shutter speed will give

an equivalent exposure. So, for

example: 1/30 sec at f/5.6 is the

same as 1/60 sec at f/4 is the same

as 1/125 sec at f/2.8 is the same

as 1/250 sec at f/2 and so on.

(The diagram is an example only

and relates to aperture and shutter

speed combinations for a light

meter reading of EV10.)

Each stephalves

Each stepdoubles

Each stepdoubles

f/1more light

1000less time

less lightf/32

more time1

Aperture

durationduration

inte

nsity

inte

nsity

Shutterspeed

f/22 2

f/16 4

f/11

f/8

f/5.6

f/4

f/2.8

f/2

f/1.4

8

15

30

60

125

250

500

Each stephalves

Title:Basic Design-ExposureSize:AVA Book Pte Ltd

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1 2 3 4 5 6 7 8 9 10 OKWhile every effort has been taken to carry out instruction to customers satisfaction NO RESPONSIBILITY liability will be accepted for errors CUSTOMERS ARE THEREFORE URGED TO CHECK THOROUGHLY BEFORE AUTHORISING PRINT RUNS DALIM

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COLOR THEORY

Hue Hue is what we see as color SaturaWon Brightness

COLOR THEORY

Understanding color temperature Amazing thing about brain

COLOR THEORY

SaturaWon

12 Part I: The Basics of Color Editing

Figure 1-2: A green patch shown at different levels of saturation.

Figure 1-3: These three cyan color patches vary in brightness values, from least bright on the left to brightest on the right.

(a) Highly saturated (b) Less saturated than a

(c) Greatly desaturated (d) Completely desaturated (no color)

a b

c d

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12 Part I: The Basics of Color Editing

Figure 1-2: A green patch shown at different levels of saturation.

Figure 1-3: These three cyan color patches vary in brightness values, from least bright on the left to brightest on the right.

(a) Highly saturated (b) Less saturated than a

(c) Greatly desaturated (d) Completely desaturated (no color)

a b

c d

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Brightness (Least bright to max bright)

Inverse square law

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Basic theory 12_13

The inverse square lawThe inverse square law states that the intensity of light observed from a constant source fallsoff as the square of the distance from the source.

Any light source that spreads its light in all directions obeys this law. In the real world, this iswhy it gets dark so quickly as you move away from the campfire!

Put simply, the inverse square law means that as you double the distance from the light youquarter the light intensity. In fact, the light falls off as 1 over (inverse) the distance multiplied byitself (squared). The light measured at 2 metres from a light source will be 1/22 or 1/4 theintensity at 1 metre. The light measured at 4 metres from the same source will be 1/42 or1/16th the intensity at 1 metre.

Photographically speaking, as every stop means a halving or doubling of light, 1/4 the amountof light is 2 stops down; 1/16th of the light is 4 stops down. Therefore, a light meter readingf/16 at 1 metre, for example, would read f/8 at 2 metres and would read f/4 at 4 metres.

It is important to understand this law, as it is one of the main ways in which light intensity canbe controlled in the studio. The only light source that does not obey this law is the sun – as anydistance we move something on earth is trivial compared to the distance from the earth to thesun.

Inverse square law

1 metre

2 metres 1/4 as bright

4 metres 1/16th as bright

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Intensity of light falls of as the square of the distance from the source. In other words, if you double the distance, the intensity is 1/4th

Depth of field 78_79

How points on subjects in front of and behind the point of critical focus reproduce as blur

circles inside the camera

A degree of blur is acceptable, as the blur circle cannot be distinguished from a point in the final image

– this gives depth of field. Smaller ‘circles of confusion’ appear as aperture is reduced (up to the point at

which diffraction effects begin (close to minimum aperture)).

maximum acceptableblur circle

distant

focusedhere

near

aperture film orsensor

depth of field

focused here

much greater depth of field


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Why RAW? RAW files 126_127

JPEG TIFF

-

-

-

-

-

-

-

-

Colour space

Image size, bit depth and resolution

Orientation and crop

Shadows and highlights

Brightness and contrast

White balance

Colour saturation

Sharpening

Noise reduction

Choose bit depth (8- or 16-bit)

Choose image size

Choose tone curve (contrast)

Choose colour space (sRGB or Adobe RGB (1998))

Set white balance

Choose amount of sharpening

Choose amount of noise reduction

-

Choose ISO sensitivity

Exposure criticalExposure important

RAW

Choose compression

Pre

-sho

otC

aptu

reP

ost-

proc

essi

ng

Anything you do tends to degrade quality

Non

-des

truc

tive

The reason for converting RAW files on your computer and not in your camera is that all theoperations involved are very processor-intensive tasks. Better results come from the greaterprocessing power of the desktop computer than from the camera’s on-board processor, whichis limited for reasons of power consumption and space. An additional advantage is that theoriginal RAW file is never altered. Instead an ‘instance’ of that file is produced using thesettings you have chosen in the RAW conversion software.


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RAW files 126_127

JPEG TIFF

-

-

-

-

-

-

-

-

Colour space

Image size, bit depth and resolution

Orientation and crop

Shadows and highlights

Brightness and contrast

White balance

Colour saturation

Sharpening

Noise reduction

Choose bit depth (8- or 16-bit)

Choose image size

Choose tone curve (contrast)

Choose colour space (sRGB or Adobe RGB (1998))

Set white balance

Choose amount of sharpening

Choose amount of noise reduction

-

Choose ISO sensitivity

Exposure criticalExposure important

RAW

Choose compression

Pre

-sho

otC

aptu

reP

ost-

proc

essi

ng

Anything you do tends to degrade quality

Non

-des

truc

tive

The reason for converting RAW files on your computer and not in your camera is that all theoperations involved are very processor-intensive tasks. Better results come from the greaterprocessing power of the desktop computer than from the camera’s on-board processor, whichis limited for reasons of power consumption and space. An additional advantage is that theoriginal RAW file is never altered. Instead an ‘instance’ of that file is produced using thesettings you have chosen in the RAW conversion software.


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Exposure Values

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2nd

What is light?

Table of exposure values (ISO 100)

shutter (s)60301584211/21/41/81/151/301/601/1251/2501/5001/10001/20001/40001/8000

1-6-5-4-3-2-10123456789

10111213

1.4-5-4-3-2-10123456789

1011121314

2-4-3-2-10123456789

101112131415

2.8-3-2-10123456789

10111213141516

4-2-10123456789

1011121314151617

5.6-10123456789

101112131415161718

80123456789

10111213141516171819

11123456789

1011121314151617181920

1623456789

101112131415161718192021

223456789

10111213141516171819202122

32456789

1011121314151617181920212223

4556789

101112131415161718192021222324

646789

10111213141516171819202122232425

Exposure Value (EV) number single number representing a range of equivalent combinations of aperture and

shutter speed. Exposure Value unit is one stop

light meter (exposure meter) measures intensity of light for photography, giving value as a combination of

shutter speed and aperture or a single EV number for a given film speed or sensitivity

f-number

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Exposure

Exposure valueExposure Value (EV) numbers are a way to describe exposure settings with just a singlenumber, instead of the usual f-stop and shutter speed combinations. A single numberrepresents all combinations of apertures and shutter speeds that give the same exposure. Forexample, EV10 in the table can represent any combination of aperture and shutter speed from4 sec at f/64 to 1/1000 sec at f/1.

Professional standard light (exposure) meters commonly have a display of the measured lightin EV numbers in addition to the f-stops and shutter speeds. The EV unit is one stop. Manyprofessional photographers prefer to think in terms of exposure values as it helps them dealwith the light and not the camera settings. For any given amount of light, there are many waysin which the camera settings of aperture and shutter speed can be combined to produce acorrect exposure in accordance with the law of reciprocity. This states that an increase in lightintensity must be matched by a corresponding decrease in the duration of the light to achievea correct exposure. It was once common for amateur mid-20th century cameras to be setusing a single EV number, now only certain professional camera lenses retain this convenience.The EV number is transferred from the light meter to the lens, which locks the shutter speedsand apertures in the appropriate relationship, from which a suitable pair can then be chosen.

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EV+ increases exposure (brightens the shot) EV – decreases exposure (darkens the shot)

USE OF FLASH

•  When do we use flash? –  In low light?

•  Using flash as a fill in during the day Wme

20

INDOOR FLASH

Which has a more natural segng?

USE OF FLASH

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First and second curtain syncIt is possible to synchronise the flash burst either at the beginning of the exposure or at theend. When the flash goes off first, it is described as first or front curtain sync (after the shuttercurtains). This kind of exposure gives a crisp image followed by the blurred exposure. Usingthis technique in the dark with a moving vehicle will produce an unnatural image with whatappears to be a stationary vehicle with speed lines coming from the front. Synchronising at theend of the exposure, so-called second or rear curtain sync, will give the expected result of avehicle trailing blurred lines.

Whether front or rear sync, it is possible to use slow flash synchronisation to great effect toemphasise movement without losing subject clarity. It is common for photographers tointentionally move the camera in a circle or jog it from side to side during a slow sync picture toensure the ambient light component of the picture is aesthetically blurred. The flash will thensuperimpose a crisp image of the subject into the blurred background. The exposureguidelines for balancing ambient and flash apply as slow sync can be considered an extremeform of fill flash (see pages 106–7).

Newry wheelers (facingopposite)Slow speed front curtainsynchronisation with somecamera panning creates agood combination of motionblur and a crisp well-litimage that captures thedrama of competition in athree-day road race.Photographer: Phil McCann.

Technical summary: Canon EOS

300D, Canon 18–55mm, 1/60 sec

a f/8, ISO 100, Canon Speedlite

420EX.

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Photographic light

Flash sync on first curtain (Front sync)

Flash sync on second curtain (Rear sync)

Resulting image

Resulting image

end

end start

Exposure

Exposure

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start

•  Front or rear flash

USING FLASH FILL

•  Use flash fill (leh) to light up the face

LIGHTING: Shadows

•  Shadows can create a lot of drama in the picture. Look for them around you

LIGHTING: When light reaches

36 Light: how images form

The nearer your subject comes to being one focal length from thelens, the bigger and further away its sharp image becomes. When it isexactly one focal length away no image forms at all; light passes out ofthe lens as parallel rays. (This is the reverse of imaging a subjectlocated at infinity, Figure 2.17.)

Check out all these imaging zones for yourself, using a converging-lens reading glass and piece of tracing paper. It is always helpful toknow (at least roughly) where and what size to expect a sharp image,especially when you are shooting close-ups, or printing unusual sizeenlargements. Ways of calculating detailed sizes and distances areshown on page 305.

Summary. Light: how images form

! Light travels in straight lines, as if in wave motion. Wavelengths aremeasured in nanometers. Light forms a tiny part of a much widerrange of electromagnetic radiation. It transmits energy in the form of‘photons’.

! Your eyes recognize wavelengths between 400 nm and 700 nm asprogressively violet, blue, green, yellow, red – the visible spectrum.All colours if present together are seen as ‘white’ light.

Figure 2.19 The closer the subjectto a lens, the greater the distanceit needs to bring the light intosharp focus. Light rays from adistant subject point are moreparallel, so the same lens bendingpower brings them to focusnearer to the lens

Figure 2.20 Conjugate distances.The positions where subjects atdifferent distances from a lens aresharply imaged

20th Century Photographers

26

Ralph Gibson From: The Sonambulist, 1968 Gibson preferred black and white and grainy work iniWally. This picture became his signature photo

COLOR THEORY

27 Reference material, not for copy.

Property of DPC

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Basic theory 14_15

Photographers find it useful to put the colours of the spectrum on a wheel, which helps inunderstanding how to filter and manipulate light. Red, green and blue will be found 120° aparton the wheel (at the 12 o’clock, 4 o’clock and 8 o’clock positions). All other colours ascombinations of the three primaries lie in between. In colour correction, you use oppositecolours on the wheel to cancel each other out. For instance, an image with a particular bluecast can be corrected by adding the yellow that lies opposite that blue on the colour wheel.The black-and-white photographer, wanting to darken the sky’s appearance, would choose ared filter opposite to the sky’s colour (cyan) on the wheel.

Digital camera users will often find hue (colour) adjustments described as a certain number ofdegrees. This represents a shift in colour around the colour wheel through an arc of that angle,rather like moving a few minutes round a clock face.

Adjustments to colour images in computer software make sense when you understand thecolour wheel. Imagine a strip taken from round the edge of the wheel being used to show every possible colour – it would start and end at the same place (cyan, in the case of thePhotoshop sliders).

Yellow

Green

Magenta

Blue

Cyan

The colour wheel Red

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COLOR THEORY 10 Part I: The Basics of Color Editing

Figure 1-1: This simple color wheel shows red, green, and blue hues.

The first thing you might question is the yellow patch, made from green plusred. Keep in mind that you’re mixing light, not paint. Mix equal parts of redand green light, and you get yellow. No, we’re not making this up! Your eyessee yellow when something you’re looking at emits equal parts of green andred light.

Still doubt us? Well, paint a yellow patch on your monitor in an Elements file,then zoom in and look very closely at the monitor. The only colors you seeare little, glowing pixels of green and red. It’s counter-intuitive, but green andred light make yellow.

Red

Yellow(Red + Green) Magenta

(Red + Blue)

Blue

Cyan(Green + Blue)

Green

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WHITE BALANCE

•  Use different segngs to get different results in your picture. •  Cloudy or shadows to get warm picture

LIGHTING SCHEME

LIGHTING SCHEME EXAMPLE

Too dark subjects

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Black cat (left)The kind of subject that demands accuratemetering. A reflected meter (in-camera)reading would produce – without exposure compensation – a mid-greyimage of this cat.Photographer: Brad Kim.

Technical summary: Canon EOS 10D, Canon EF

70–200mm f/2.8L zoom lens at 200mm focal length.

Underexposed by 2 stops from the camera meter

reading. Photoshop levels applied for final tonal

adjustment.

White tulips (below)Another difficult subject to expose by using a reading from a reflected light meter. Withoutpositive EV compensation (up to 2 stops overexposure on reading) these tulips would be grey.Photographer: Marion Luijten.

Technical summary: Canon 10D Sigma 105mm 1/125 sec at f/13 ISO 400, lit by two Bowens Esprit 500DX

monoblocs, one with softbox and one with umbrella.

Exposure 34_35

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Too much brightness

QC Preflight Point

88QC Preflight Point

2nd 88

Job no : 75902 Title : BP-Lighting Client : AVAScn : #175 Size : 160(w)230(h)mm Co : M8 C (All To Spot)(Coagl) Dept : DTP D/O : 05.12.06 (Job no: 75902C1 D/O : 26.12.06 Co: CM3)

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Black cat (left)The kind of subject that demands accuratemetering. A reflected meter (in-camera)reading would produce – without exposure compensation – a mid-greyimage of this cat.Photographer: Brad Kim.

Technical summary: Canon EOS 10D, Canon EF

70–200mm f/2.8L zoom lens at 200mm focal length.

Underexposed by 2 stops from the camera meter

reading. Photoshop levels applied for final tonal

adjustment.

White tulips (below)Another difficult subject to expose by using a reading from a reflected light meter. Withoutpositive EV compensation (up to 2 stops overexposure on reading) these tulips would be grey.Photographer: Marion Luijten.

Technical summary: Canon 10D Sigma 105mm 1/125 sec at f/13 ISO 400, lit by two Bowens Esprit 500DX

monoblocs, one with softbox and one with umbrella.

Exposure 34_35

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1/125 s f/13 ISO 400

4.light n color

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