Abook like Langford's Basic Photography is a fantastic introduction to a wonderful cameras have a precision, manual rangefinder system (Figure ). Langford's Basic Photography PDF By:Michael John Langford,Anna Fox,Richard Sawdon Smith Published on by Taylor & Francis. langfords basic photography is a seminal photography text. serious photographers michael langford's starting photography pdf - photography program for.
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Langford's Starting Photography is a hands-on book for those photographers just reflex (SLR) cameras (preferably with manual controls), and the knowledge. 1. 2. LANGFORD'S BASIC PHOTOGRAPHY. Another reason for taking up photography is that you want a means of personal self-expression to explore your own. Once you've read about the history of nude photography, the many ways you can sharpen. the Czech Pascal Baetens Intro to Fine-Art Black & White.
You can help by adding to it. July Play media Driving from Roe Highway northbound, along a looped interchange ramp, to Great Eastern Highway eastbound Most junctions on the highway are grade separated diamond interchanges south-west of Tonkin Highway, and at-grade traffic light controlled intersections to the north-east of Tonkin Highway. The exceptions are at: Great Eastern Highway, a modified diamond interchange with a northbound to eastbound loop ramp; Clayton Street and Maida Vale Road, which are grade separated, but with only northbound exit and southbound entry ramps; and the terminus at Kwinana Freeway, a trumpet interchange. There is a diamond interchange at Tonkin Highway, with the free flowing traffic on Tonkin Highway, and traffic light controlled intersections on Roe Highway at the entry and exit ramps. The highway was intended to form the southern and eastern sections of a ring route around the Perth metropolitan area. The 4. It may in the future be upgraded to a freeway classification.
The skills and knowledge presented in the book show you how to take and make great photographs using a highly visual step-by-step approach. The photographic examples scattered throughout the text are chosen to encourage and challenge the reader, as they are all within the technical capabilities of beginners with modest gear, such as compact or single lens reflex SLR cameras preferably with manual controls , and the knowledge and skill provided within.
Taking photographs is enjoyable and challenging in all sorts of ways. What photography demands of you are skills of a different sort that are independent of the technology used to capture the picture. Avoid taking these things for granted just because they are familiar. Develop your awareness of the way lighting and viewpoint can transform appearances, and be quick thinking enough to capture an expression or sum up a fast-changing situation by selecting the right moment to shoot.
Become skilled in these areas and you will be a good photographer. It is just that you should keep in the forefront of your mind that the techniques and ideas presented in this text serve only one purpose. That is, to support the creation of images that you see with your eye first and capture with your camera second. He was a fellow and Course Director in Photography at the Royal College of Art and was renowned for producing a string of 24 books, translated into many languages, which have remained the standard reference works for students and professionals alike across the world.
After his national service, he had a brief spell with a press photography firm, moving on to work as an industrial photographer while teaching evening classes. Michael continued as a professional photographer throughout his life and his work has appeared in a range of mediums, from postage stamps and book covers to TV commercials.
He served as an external assessor for several BA courses, as well as an adviser to national examination boards for photography at school and college levels. He moved to the RCA in , became a senior tutor in , departmental head 12 years later and from to he suitably held the position as course director. As a result of his intimate involvement with photography courses and examination syllabuses at all levels he fully understood what a student needed from a textbook. One of his most successful books, Basic Photography, was first published in and the work for the seventh edition was completed just a few days before he died aged 67, bringing it right up to date with the inclusion of information on digital photography.
Many of his books have been adapted as standard texts, bibles for generations of photographers who owe their careers to his work and are still used today for courses from high school to university.
As a writer, teacher and practitioner Michael Langford was a legend in the world of British photography. Michael Langford, photographer, teacher and writer 28 February —28 April Picture Making 1 This first section of the book is mainly concerned with developing your skills of observation — and how to select the interesting and unusual from what you see around you. It is concerned with picture-composing devices such as: framing up your shot in the camera viewfinder or LCD monitor; choice of viewpoint and moment to shoot; and picking appropriate lighting.
It also discusses how to recognize pattern, line, color and tone in the subject you intend to photograph, and how to use such features to good effect. These are visual rather than technical aspects of photography and most stem from drawing and painting. They apply no matter what camera you own — cheap or expensive, digital or film, auto-everything or covered in dials and controls. They may be Avery sophisticated technically, but they cannot see or think for themselves.
Bicycles enable you to get out and explore the world; cameras challenge you to make successful pictures out of what you see around you, in perceptive and interesting ways. Anyone who starts photography seriously quickly discovers how it develops their ability to see. In other words, not just taking familiar scenes for granted but noticing with much greater intensity all the visual elements — shapes, textures, colors and human situations — they contain.
This is an exciting and rewarding activity in itself. The second challenge is how to put that mindless machine the camera in the right place at the right time, to make a really effective photographic image out of any of these subjects. To begin with, it is helpful to consider the ways seeing differs from photographing. This makes it much easier to work through your camera. However, immediately you look through a camera viewfinder the world is cut down into a small rectangle with sharply defined edges and corners.
Pictorialism and realism By the beginning of the twentieth century equipment and materials had become somewhat easier to handle. Snapshot cameras, and developing and printing services for amateurs, made black and white photography an amusement for the masses.
Changing attitudes towards photography 13 Figure 1. They made maximum use of the qualities of black and white photography previously condemned: Technical excellence was all important and strictly applied. Photography had an aesthetic of its own, but something quite separate from painting and other forms of fine art.
The advent of photographs mechanically printed into newspapers and magazines opened up the market for press and candid photography. Pictures were taken for their action and content rather than any greatly considered treatment. This and the freedom given by precision hand cameras led to a break with age-old painterly rules of composition. Demachy made his prints by the gum bichromate chemical process, which gives an appearance superficially more like an impressionist painting than a photograph The s and 40s were the great expansion period for picture magazines and photo-reporting, before the growth of television.
They also saw a steady growth in professional aspects of photography: Most of this was still in black and white. Use of colour gradually grew during the s but it was still difficult and expensive to reproduce well in publications. Youthful approach of the s Rapid, far-reaching changes took place during the s. From something which a previous generation had regarded as an old-fashioned, fuddy-duddy trade and would-be artistic occupation, photography New small-format precision SLR cameras, electronic flash, machines and custom laboratories to hive off boring processing routines, and an explosion of fashion photography, all had their effect.
Photography captured the public imagination. Young people suddenly wanted to own a camera, and use it to express themselves about the world around them. The fresh air this swept into photography did immeasurable good.
Photography began to be taught in schools and colleges, especially art colleges, where it had been previously down-graded as a technical subject. America led the way in setting up photographic university degree courses, and including it in art and design, social studies and communications. Nevertheless, few one-person portfolios of photographs had been published with high quality reproduction in books.
It was also extremely rare for an established art gallery to sell or even hang photographs, let alone public galleries to be devoted to photography. As a result it was difficult for the work of individuals to be seen and become well-known. Even magazines and newspapers failed to credit the photographer alongside his or her work, whereas writers always had a published credit. By the s though all this had changed.
Adventurous galleries put on photography shows which were increasingly well attended. Demand from the public and from students on courses encouraged publishers to produce a wide range of books showcasing the work of individual photographers. The s brought colour materials which gave better quality results and were cheaper than before.
Colour labs began to appear offering everyone better processing and printing, plus quicker turn-around. The general public wanted to shoot in colour rather than black and white, and gradually colour was taken up by artist photographers too.
Colour became cheaper to reproduce on the printed page; even newspapers started to use colour photography. Today the availability of less daunting, user-friendly camera equipment combined with a much bigger public audience for photography and more willing to receive original ideas encourages a broad flow of pictures. Galleries, books and education have brought greater critical discussion of photographs — how they communicate meanings through a visual language of their own.
There are now so many ways photography is used by different individuals it is becoming almost as varied and profound as literature or music.
Personal styles and approaches Figure 1. A rapid sequence of three ultra-fast flash exposures made on one frame of film and shot in a specially devised laboratory setup, by Stephen Dalton. For example, are you mostly interested in people or in objects and things you can work on without concern for human relationships?
Do you enjoy the split-second timing needed for action photography, or prefer the slower more soulsearching approach possible with landscape or still-life subjects? If you aim to be a professional photographer you may see yourself as a generalist, handling most photographic needs in your locality. Or you might work in some more specialized area, such as natural history, scientific research or medical photography, combining photography with other skills and knowledge.
Some of these applications give very little scope for personal interpretation, especially when you must present information clearly and accurately to fulfil certain needs. There is greatest freedom in pictures taken by and for yourself. Here you can best develop your own visual style, provided you are able to motivate and drive yourself without the pressures and clear-cut aims present in most professional assignments. Style is difficult to define, but recognizable when you see it.
Pictures have some characteristic mix of subject matter, mood humour, drama, romance, etc. Technique is important too, from choice of lens to form of print presentation. But more than anything else style is to do with a particular way of seeing. Personal styles and approaches 17 Figure 1. It comes out of doing, rather than of analysing too much, refined down over a long period to ways of working which best support the things you see as important and want to show others.
It must not become a formula, a mould which makes everything you photograph turn out looking the same. The secret is to coax out the essence of each and every subject, without repeating yourself. People should be able to recognize your touch in a photograph but still discover things unique to each particular subject or situation by the way you show them.
In personal work the content and meaning of photographs can be enormously varied. Her quiet observation explores connections between the Caribbean and Europe by tracing fragments of history. The picture Figure 1. Compare with Figure 1. Detailed and strongly narrative, her individually untitled pictures represent little moments of familiarity — the kind of undramatic, ordinary observations and experiences of life.
In Figure 1. A dramatic black and white interpretative image of great simplicity. It was seen and photographed straight but printed with very careful control of tonal values What is photography? Personal styles and approaches 19 her reflection with both anxiety and pleasure. Other elements contained in the room say something about earlier times. Her people are posed by actresses and every item specially picked and positioned.
Content and meaning rule here over authenticity, but are based on acute observation and meticulous planning. Bear in mind here that tableaux pictures of constructed events have a long history in photography. Victorians like Julia Margaret Cameron and H. Robinson produced many photographs narrating stories. Sometimes the content of personal work is based on semi-abstract images in which elements such as colour, line and tone are more important than what the subject actually is.
Meaning gives way to design and the photographer picks subjects for their basic graphic content which he or she can mould into interesting compositions. Look at collections of work by acknowledged masters of photography single pictures, shown in this book, cannot do them justice: Cindy Sherman, John Pfahl, Martin Parr and Mari Mahr are photographers who each have dramatically different approaches to content and meaning. Their work is distinctive, original, often obsessional.
Her pictures explore how people view others from a different part of the world The content and meaning of each shot relate to little moments familiar to experiences in everyday life. The real and the fictional are combined here, see text What is photography? Measuring success There is no formula way to judge the success of a photograph.
Most commercial photographs can be judged against how well they fulfil their purpose, since they are in the communications business. A poster or magazine cover image, for example, must be striking and give its message fast. But many such pictures, although clever, are shallow Measuring success 21 Figure 1.
You might read it as landscape, or as flat, twodimensional abstract design — a piece of artwork complete in itself and soon forgotten. There is much to be said for other kinds of photography in which ambiguity and strangeness challenge you, allowing you to keep discovering something new.
This does not mean you have to like everything which is offbeat and obscure; there are as many boring, pretentious and charlatan workers in photography as in any other medium. Reactions to photographs change with time too. Live with your picture for a while have a pinboard wall display at home otherwise you will keep thinking your latest work is always the best.
A great deal of professional photography is sponsored, commercialized art in which success can be measured financially. Personal projects allow most adventurous, avant-garde picture making — typically to express preoccupations and concerns. Artistic success is then measured in terms of the enjoyment and stimulus of making the picture, and satisfaction with the result.
Rewards come as work published in its own right or exhibited on a gallery wall. Extending yourself in this way often feeds commercial assignments too. So the measure of true success could be said to be when you do your own selfexpressive thing, but also find that people flock to your door to commission and download this very photography.
What is photography? It requires craftsmanship and artistic ability in varying proportions.
Technical knowledge is necessary if you want to make full use of your tools and so work with confidence. Always explore new processes and equipment as they come along. Discover what kind of images they allow you to make. Traditionally in photography the image of your subject formed by the camera lens is recorded on silver halide coated film.
Processing is by liquid chemicals, working in darkness. New technology now allows us the option of capturing the lens image by electronic digital means. Results can also be manipulated digitally, using a computer. Visually, camera work in colour is easier than black and white.
Colour is more complex in the darkroom. Photography records with immense detail, and in the past had a reputation for being essentially objective and truthful. Taking photographs calls for a mixture of a carefully followed routines and craft skills, to control results, and b creative decisions about subject matter and the intention of your picture. The public once viewed photography as a stuffy, narrow pseudo-art, but it has since broadened into both a lively occupation and a creative medium, exhibited everywhere.
Developing an eye for composition helps to simplify and strengthen the point of your picture. Avoid slavishly copying their style. It might be measured in technical, financial or purely artistic terms, or in how effectively it communicates to other people. In an ideal world all these aspects come together.
Projects When you are working on projects it is helpful to maintain your own visual notebook. This might be a mixture of scrapbook and diary containing written or sketched ideas for future pictures, plus quotes and work by other photographers, writers or artists which you want to remember add notes of your own. It can also log technical data, lighting diagrams and contact prints relating to shots planned or already taken. The projects below can be completed in either written or verbal discursive form, but they must include visual material such as prints, photocopies or slides.
Some suggested photographers: Comment on their effectiveness. In preparation for this project look at work by some of the following photographers: But understanding the practical principles behind photography and photographic equipment gives you a broader, more flexible approach to problem solving. It is also interesting. For example, the way light is manipulated to form images is not really very complicated — did you know it can be done with a hole in a card?
We start with the very foundation stone of photography, which is light. What precisely is light, and which of its basic features are helpful to know when you are illuminating a subject, using lenses and learning about colour? From light and colour we go on to discuss how surfaces and subjects look the way they do, and why light has to be bent with glass to create a usable image.
The lens is without doubt the most important part of any camera or enlarger. Starting with a simple magnifying-glass lens you can begin to see how photographic lenses form images. Later this will lead us on to other key components of camera equipment. Light itself Figure 2. And yet you are so familiar with light you almost take it for granted. Light is something your eyes are sensitive to, just as your ears relate to sound and your tongue to taste. It is the raw material of sight, communicating information about objects which are out of range of other senses.
Using light you can show up some chosen aspects of a subject in front of the camera and suppress others. Light channels visual information via the camera lens onto photographic material, and enables you to enjoy the final result. At this very moment light reflected off this page carries the shape of words to your eyes, just as sound would form the link if we were talking. But what exactly is light? Visible light is a stream of energy radiating away from the sun or similar radiant source.
Its four important characteristics, all present at the same time, are: Wavelengths and colours Figure 2. Different wavelengths give our eyes the sensation of different colours. It moves less fast in air, and slightly slower still in denser substances such as water or glass. These bleach dyes, cause chemical changes in films and electronic response in digital camera sensors, etc. The more intense the light, the more photons it contains.
As shown left, this includes radio waves with wavelengths of hundreds of metres through to gamma and cosmic rays with wavelengths of less than ten thousand-millionths of a millimetre. Each band of electromagnetic radiation merges into the next, but has its own special characteristics.
Some, such as radio, can be transmitted over vast distances. Others, such as X-rays, will penetrate thick steel, or destroy human tissue. Your eyes are only sensitive to a narrow band between wavelengths nm and nm approximately. A nanometre or nm is one millionth of a millimetre. This limited span of wavelengths is therefore known as the visible spectrum.
But if only some wavelengths are present the light appears coloured. For example, in Figure 2.
This alters to blue if wavelengths are changed to — nm. Between nm and nm the light looks more blue-green, and from about nm to nm you see yellow. The yellow grows more orange if the light wavelengths become longer; at nm it looks red, becoming darker as So the colours of the spectrum — violet, blue, green, yellow and red — are really all present in different kinds of white light sunlight, flash or studio lamps for example.
The human eye seems to contain three kinds of light receptors, responding to broad overlapping bands of blue, green and red wavelengths. When all three receptors are stimulated equally by something you see, you tend to experience it as white, or neutral grey.
If there is a great imbalance of wavelengths — perhaps the light contains far more red long waves than blue short waves — stimulus is uneven.
Light in this case may look orange tinted, just as happens every day around sunrise or sunset. Try to remember the sequence of colours of the visible spectrum. Later you will see how the concept of three human visual receptors together responding to the full colour spectrum is adapted to make photographic colour films work too.
It seems odd that humans can biologically sense only a relatively tiny part of the vast electromagnetic spectrum. Shadows Light travels in straight lines and in all directions from a light source.
Objects throw contrasty, sharp-edged shadows. Figure 2. A larger source — simply formed here by inserting a large sheet of tracing paper — gives a soft, graduated shadow. See also Figure 7. When light reaches a surface Figure 2. But look what happens when you place tracing paper in the light beam or block the direct light and reflect the remainder off a matt white wall, Figure 2.
Tracing paper passes light but also diffuses it. The light passed through the paper scatters into new straight lines proceeding in all directions from every part of its large area surface. The object you were illuminating now casts a softer-edged, graduated shadow, and the larger and closer your diffusing material the less harsh and contrasty the shadow becomes.
This is because light from a large area cannot be completely blocked out by the subject; most of the parts previously in shadow now receive at least some illumination. The same would happen with sunlight on an overcast day. Shadow qualities greatly influence the way subjects and scenes look. Bear in mind this is not something you can alter in a photograph by some change of camera setting or later manipulation. Understanding and 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 the material, 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 for example — 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 a shiny metal one.
If the material is also coloured it reflects wavelengths of this colour and absorbs most of the other wavelengths present in the light. For example blue paint reflects blue, and absorbs red and green from white light. But if your light is already lacking some wavelengths this will alter subject appearance. To take an extreme case, when lit by deep red illumination, a rich blue will look and photograph black, see Figure 2.
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 matt surface such as an eggshell, drawing paper or dry skin scatters the light evenly. The angle from which light strikes it makes very little difference.
However, if the surface is smooth and reflective it acts more like a mirror, and reflects almost all the light back in one direction. This is called specular reflection. If your light strikes the shiny surface at right angles it is reflected backward along its original path. You get a patch of glare, for example, when flash-on-camera shots are taken flat on towards a polished glass window or gloss-painted wall. But if the light is angled it reflects off such surfaces at the same angle from which it arrived, Figure 2.
So try to arrange your lighting direction or camera viewpoint to bounce glare light away when photographing a highly reflective surface. If you are using built-in flash angle your camera viewpoint. Light reflected from a matt surface scatters relatively evenly.
Oblique light directly reflects off at the same angle as it arrived incident. Coloured materials selectively reflect and absorb different wavelengths from white light. However, appearance changes when the viewing light is coloured Materials transparent or translucent to light Not every material is opaque to light, of course.
Clear glass, plastic and water for example are transparent and transmit light directly, while tracing paper, cloud and ground glass diffuse the light they transmit and are called translucent. In both cases if the material is coloured it will pass more light of these wavelengths than other kinds.
Deep red stained glass transmits red wavelengths but may be almost opaque to blue light, see Figure 2. Since translucent materials scatter illumination they seem milky when held up to the light and look much more evenly illuminated than clearer materials, even when the light source is not lined up directly behind.
Slide viewers work on this principle. The quality of the light is similar to that reflected from a white diffused surface. Refraction Interesting things happen when direct light passes obliquely from air into some other transparent material. As was said earlier, light travels slightly slower when passing through a denser medium. When light passes at an angle from air into glass, for example, its wavefront remember the ripples on the water, Figure 2. This is because one part reaches the denser material first and skews the light direction, like drawing a car at an angle into sand, Figure 2.
A new straight-line path forms, slightly steeper into the glass more perpendicular to its surface. The change of light path when light travels obliquely from one transparent medium into another is known as refraction. When light reaches a surface 29 Figure 2. Diffusely transmitting materials milky plastic, ground glass scatter light fairly evenly. Clear materials pass most of the light directly. Angled light is part reflected, mostly refracted.
Coloured materials pass only selected wavelengths from white light. When the viewing light is a colour different to the material, no light may get through You can see refraction at work when you poke a straight stick into clear water; it looks bent at the water surface. Again, looking obliquely through a thick, half-closed window, parts of the view through the glass look offset relative to what can be seen direct.
But most importantly because of refraction, lenses bend light and so form images, as we will come to shortly. Remember that refraction only bends oblique light. Light which strikes the boundary of two transparent materials at right angles slows minutely but does not change direction.
And most light reaching the boundary at a very low angle very oblique is reflected off the surface. The whole picture In practice then the range of objects around us appear the way they do because of the mixture of effects they have on light — diffuse and Figure 2.
Light slows when passing from air into glass. Wavefronts slow unevenly if light reaches the denser medium obliquely left. The effect is like driving at an angle from the highway onto sand right. Uneven drag causes change of direction. Light striking the boundary at right angles centre slows but does not alter direction An apple side-lit by direct sunlight for example reflects coloured wavelengths strongly from its illuminated half.
Most of this is diffusely reflected, but part of its smooth skin reflects a bright specular highlight, just where the angle of the sun to the surface matches the angle from this point to your eye.
The shape and relative darkness of the shadow to one side of the apple gives you further clues to its form.
This is essentially what optical aspects of seeing and photographing objects are all about. Light intensity and distance Figure 2. Light would be communicating information about its different parts to you in a mixture of ways. The water jets transmit and refract light, glittering parts of the lake surface specularly reflect, while the grey stone diffusely reflects light.
What little light from the sky alone reaches shadowed areas beneath the fountain is mostly absorbed by blackened stone The closer your light source is to your subject the brighter it will be illuminated. For example, if you are using a small flashgun or studio lamp to light a portrait, halving its distance from the subject gives you four times the light, so exposure can be quartered.
The same applies to printing exposures when you alter enlarger height Chapter 13, and in close-up situations, page Making light form images 31 when lighting a number of items at different distances in a small studio, using a harsh compact light source such as a spotlight. It may then be impossible to correctly expose items nearest and farthest from the light at any one exposure setting. The same problem does not arise with direct sunlight outdoors. The sun is so vastly far away that any two places on earth — be they seashore or mountain peak — are almost equal in distance from the sun.
Intensity will then alter with distance in the same way as if you had a lamp this size in the same position. Making light form images Suppose you set up and illuminate a subject, and just face a piece of tracing paper or film towards it. You will not of course see any image on the sheet. The trouble is that every part of your subject is reflecting some light towards every part of the paper surface. This jumble of light simply illuminates it generally. The same light spreads over four times the area.
Since light travels in straight lines, those light rays from the top of the subject able to pass through the hole can only reach the bottom part of the paper. And light from lower parts of the subject only reaches the top of the paper Figure 2. As a result your paper sheet shows a dim, rather fuzzy upside-down representation of the subject on the other side of the pinhole. The best way to see a pinhole image is to be in a totally darkened room, with foil or black paper over the window facing a sunlit scene outside.
Make a drawing-pin size hole in the foil and hold up tracing paper about 30 cm 12 in in front of it to receive the image. You can easily take colour photographs using a pinhole if your camera has a removable lens.
See Project 1 at the end of the chapter.
So the business of actually forming an image is not particularly complicated or technical. Practical limitations to pinhole images The trouble with a pinhole-formed image is that results are not good enough for most photography see Figure 2. None of the image detail is ever quite sharp and clear, no matter where you position the Figure 2.
A sheet of paper just held up towards an illuminated subject receives a jumble of uncontrolled light rays, reflected from all its parts. A pinhole in an opaque screen restricts rays from each part of the subject to a different area of the paper; a crude upsidedown image is formed Making light form images Figure 2.
Pictures taken using a 35 mm SLR camera body fitted with left kitchen foil having a 0. When focused for the centre, the magnifier gives the poorest definition of all near picture edges. The pinhole gives slightly unsharp detail everywhere 33 tracing paper. As Figure 2.
What should be details become many overlapping discs of light which give the image its fuzzy appearance. Then again a pinhole-formed image is so dim. You can brighten it by enlarging the hole, but this makes image detail even less sharp and clear. And if you make two holes you get two overlapping images, because light from any one part of the subject can then reach the paper in two places. Even if you accept a dimmer image and try to sharpen detail by using a still smaller hole, those discs of light can obviously never be smaller than the hole itself.
And you quickly get to a point where further reduction actually makes results worse because of an optical effect known as diffraction, page The smaller and rougher the hole the greater the percentage of light rays displaced by this effect, relative to others passing cleanly through the centre. Using a lens instead The best way to form a better image is to make the hole bigger rather than smaller, then bend the broad beam of light you produce so that it narrows converges instead of continuing to expand.
This is done by using refraction through a piece of clear glass. The opposite happens when light travels from glass into air, as air is less dense. So if you use a block of glass with sides which are non-parallel Figure 2. In practice, a shaped piece of glass that is thicker in the centre than at its edges will accept quite a wide beam of diverging light and convert it into a converging beam.
Mechanically it is easiest to create this So you have a circular glass converging lens. If you position it too close or too far away, the light rapidly broadens out Figure 2.
So a lens has to be focused precisely; the correct image position will depend on the light-bending power of the lens, and the distance between lens and subject. Focal length and image size Figure 2. Think of a lens shape as a series of blocks which bend many light rays to a common point of focus The light-bending power of a lens is shown by its focal length. As shown in Figure 2. In practice this means something on the horizon.
Focal length takes into account the type of glass its refractive index and its shape. A lens with a long focal length has relatively weak bending power — it needs a long distance to bend light rays to a point of focus. The stronger the power of the lens, the shorter its focal length. The picture detail is also smaller in size than the same subject imaged by a longer focal length lens. Imaging closer subjects Figure 2. This is why out-offocus highlights become discs — Figure 2. The rule is: This is why you often see camera lenses move forwards when set for close distances, and for really close work you may have to fit an extension tube between body and lens see page Clearly there are problems when the scene you are photographing has a mixture of both distant and close detail, all of which you want in focus.
Making light form images 35 Figure 2. Droplets closer left and further away right become unsharp patches of light at this focus setting.
Notice how each patch takes on the shape of the lens diaphragm Figure 2. In the case of a simple lens, focal length is the distance between the lens and the position of a sharp image of an object at infinity Conjugate distances. For example, light from a subject located somewhere between infinity and two focal lengths from your converging lens will come into focus somewhere in a zone between one and two focal lengths on the imaging side of the lens. Where the subject is precisely two focal lengths distant the sharp image is formed two focal lengths behind the lens, as well as being exactly the same size as the subject.
Magnification height of subject divided into the height of its image is then said to be 1. When your subject is closer than two focal lengths, the image is formed beyond two focal lengths behind the lens, and magnification is more than 1.
In other words, the image shows the subject enlarged. This is the situation when a lens is used for projecting slides or making enlargements. The longer the focal length the larger the image. This is why cameras taking large format pictures need longer focal length lenses to include the same amount of your subject Light rays from a distant subject point are more parallel, so the same lens bending power brings them to focus nearer to the lens The nearer your subject comes to being one focal length from the lens, the bigger and further away its sharp image becomes.
When it is exactly one focal length away no image forms at all; light passes out of the lens as parallel rays. This is the reverse of imaging a subject located at infinity, Figure 2. Check out all these imaging zones for yourself, using a converginglens reading glass and piece of tracing paper. It is always helpful to know at least roughly where and what size to expect a sharp image, especially when you are shooting close-ups, or printing unusual size enlargements.
Ways of calculating detailed sizes and distances are shown on page Wavelengths are measured in nanometers. Light forms a tiny part of a much wider range of electromagnetic radiation. Your eyes recognize wavelengths between nm and nm as progressively violet, blue, green, yellow, red — the visible spectrum. Light from a large-area source including hard light diffused gives softer, graduated shadows.
Smooth, shiny surfaces give you specular reflection — direct light is mostly reflected all one way. Oblique illumination bounces off such a surface at an angle matching the light received. Matt surfaces scatter reflected light and are much less directional.
Transparent materials directly transmit light; translucent materials diffuse light. Light passing obliquely from one transparent material to another of different density is refracted bent more perpendicular to the surface in the denser medium. Coloured materials absorb and reflect or transmit light selectively according to wavelength. Appearance varies with the colour of the light source illuminating them.
The amount of illumination photons received by a surface area from a direct, compact light source is quartered each time its distance from the light source is doubled. Because light travels in straight lines a pinhole in an opaque material forms a crude upside-down image of an illuminated subject.
A converging lens gives you a brighter, sharper image than a pinhole, by bending a wide beam of diverging light from your subject so that it converges to a point of focus. The position of sharp focus depends on the refracting power of the lens, and subject distance. Lens power is shown by focal length, in simple optics the distance between the lens and a sharp image of an object at infinity.