تويت
الضوء - المادة الخام للتصوير الفوتوغرافي ..
مبادئ التصوير الفوتوغرافي .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
PRINCIPLES OF PHOTOGRAPHY
Light - photography's raw material
Light is fundamental to photography - the very word means " writing with light " or " drawing with light " . Without light you can neither see nor take a photograph because it is light reflected from the world around you that makes the world visible both to the human eye and to the camera .
Light , like sound , is a form of energy . It is radiated out in waves at colossal speed from a source such as the sun , an electric lamp or a flashbulb . As a form of energy , it affects the nature of materials it falls on , causing certain chemical changes to take place - skin becomes tanned by the sun , and fruit ripened . The most important feature of light for the purposes of photography . however , is that it travels in straight lines . You can see this for yourself if you observe the straight shadows formed behind objects that block light from the sun or watch rays of sunlight passing through smoke .
The behavior of light varies according to the material or surface it strikes . Opaque materials such as wood or metal block the passage of light by absorbing most of its rays . Transparent materials such as glass or water transmit light , allowing it to pass through . Textured surfaces scatter light in all directions as they reflect it , so that the light is softened and " diffused " . Clear smooth surfaces , like polished metal or glass , return the light waves without much scattering , so that you can see reflected mirror images . Most surfaces reflect some light rays back - the paler the surface , the more light it reflects . Black surfaces reflect no light , while white surfaces reflect almost all the light rays .
Light is also the source of all colors . It is composed of waves of different lengths ( called wavelengths ) , some of which are visible to the human eye and are perceived as different colors - long wavelengths as red , short wavelengths as blue - violet . The sun , as well as most other light sources , radiates a continuous spectrum of all these wavelengths , which we see as " white " " light . But objects around us absorb some wavelengths and reflect others . A ripe tomato , for example , absorbs most of the green and blue wavelengths but reflects red light , so you see it as red .
Transparent materials transmit all wavelengths equally unless they are colored . For instance , a blue stained glass window or color filter transmits blue light and absorbs all other wavelengths . Similarly , a red filter allows only red light to pass through . absorbing other wavelengths . This selective transmission is very important in photography . In black and white photography it affects the way tones reproduce , suppressing some , intensifying others ( see p . 100 ) . In color photography it is essential to the way that negative and slide film reproduce colors and to color processing and printing ( see pp . 141-3 , 162-3 ) .
Light determines the way you perceive the shape and form of objects . For example , a tomato side - lit by the sun reflects red light strongly on the lit side . Light strikes its curved surface at different angles and is therefore reflected back to your eye at different intensities . Your eyes and brain recognize that these gradations of brightness signify " roundness " without your having to touch the tomato to find out .
However , you can only see the objects around you clearly because your eyes admit only a restricted amount of light ( through a minute hole - the pupil , see page 20 ) which is then focused by the lens of the eye .
Light , lenses , and forming images
The principle of admitting light through a minute hole in order to produce a reflected image has been known since ancient times- it is the principle of the pinhole camera or " camera obscura " .
The explanation of this phenomenon is quite simple . As light travels in straight lines , light rays from the top part of the scene outdoors can only reach the bottom part of the receiving area through the pinhole , and vice versa , creating an inverted image of brighter and dimmer reflections . An image produced in this way is rather dim and ill - defined , because the hole is very small and light rays travelling from each point of the subject are slightly dispersed as they pass through the hole .
To produce a brighter and sharper image it is necessary to gather more light , and converge the light rays , that is , focus the image . This requires a lens .
When a light ray enters a transmitting material , such as glass , at an oblique angle , it is bent or " refracted " . You can see this if you put a spoon in a glass of water - from certain angles the spoon appears bent . If you make a disk of glass with curved surfaces ground thinner at the edges that at the center , you can use the principles of refraction to converge the light rays so that they meet together at one point . This is the principle on which the converging lens is based .
A converging lens transmits light rays from each part of the subject and brings them to focus on a flat surface ( such as paper or film ) . Light rays from the top and bottom , left and right parts of the subject are brought to focus on diametrically opposite parts of the receiving surface . This produces a sharp and detailed image of the subject , upside - down .
The converging lens was added to the " camera obscura " as early as the sixteenth century . It took another three hundred years to find a way of recording the image , as explained overleaf .
The qualities of light :
Light travels in straight lines The lit side of a tomato absorbs most of the light and reflects the remainder . Because light travels in straight lines , the area behind the tomato does not receive any light and a shadow is formed . Light , as a form of energy , also helps the tomato to grow and ripen .
Light can be bent When directed at an oblique angle through a glass prism the light is bent an effect known as refraction . This is because light travels more slowly through glass than through air .
Light can be reflected Different types of surfaces reflect different amounts of light . A smooth polished surface , such as a mirror , reflects most of the light reaching it . redirecting the beam . The two angles made by the light beam to the flat surface are equal .
Light can be diffused Light passed through a translucent material , such as clouds or tracing paper , is scattered in all directions . Light reflected from mat or textured opaque surfaces is also diffused . Scattered light forms less distinct , graduated shadows .
Light contains colors Light is composed of waves of different lengths ( called wave- lengths ) . Each wavelength is a particular color . The whole spectrum of colors is contained in light which appears white you can see the colors separated out naturally in a rainbow , or when light is directed at an oblique angle through a prism . Colored objects appear colored because they reflect certain wavelengths and absorb others .
Pinhole image You can form a crude image by admitting light from a brightly lit scene through a tiny hole into a dark box or room . On the surface furthest from the hole an inverted image of the scene will be visible . This is because light from the top part of the scene can only reach the bottom part of the receiving surface through the small hole , and vice versa . Details in the image are never quite sharp because the light is not bent to a point of focus but simply restricted to a narrow beam the size of the hole .
Making a pinhole image You can produce a pinhole image by using a short tube with a piece of tracing paper at one end and an opaque material with a tiny hole in the center at the other . If you hold this in a dark corner of a room with the pinhole pointing toward a brightly lit object , an inverted image will be formed on the tracing paper .
Replacing a pinhole with a lens A light converging lens solves the problems of using a pinhole to form an image . It bends incoming light to points of focus , so that each part of the subject is rendered with great clarity . The lens must be accurately distanced from the receiving surface ( focused ) so that the surface coincides with the sharp image . A lens can also be much wider in diameter than the pinhole so that the image formed is much brighter and easier to see . Try making this change yourself , using a simple magnifying glass . In fact a magnifier still has many aberrations ( optical errors ) which distort image shape and detail .
Lens shapes Lenses which are made thicker in the center than at their edges converge light . If the center is ground thinner than the edges the lens has the opposite effect on light rays - it causes them to diverge . Weak diverging lenses are combined with strong converging types in cameras to help correct aberrations in the image . The amount by which a lens converges or diverges light depends upon its thickness , and the type of glass from which it is made .
How lenses work
Refraction When passed through a block of glass , such as shown left , light rays are refracted and bent .
Converging light If two prisms are placed base to base light rays are refracted so that they bend toward each other and converge . This is the principle of the converging lens , above left , a lens used in all cameras . It is a disk of glass ground thinnest around the edges so that light rays from different directions are bent to focus on one point . A magnifying glass is a con- verging lens . It will bend the light from the sun on to a piece of paper . To form an image it must be held at a certain distance from the paper- known as the focal length of the lens .
مبادئ التصوير الفوتوغرافي .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
PRINCIPLES OF PHOTOGRAPHY
Light - photography's raw material
Light is fundamental to photography - the very word means " writing with light " or " drawing with light " . Without light you can neither see nor take a photograph because it is light reflected from the world around you that makes the world visible both to the human eye and to the camera .
Light , like sound , is a form of energy . It is radiated out in waves at colossal speed from a source such as the sun , an electric lamp or a flashbulb . As a form of energy , it affects the nature of materials it falls on , causing certain chemical changes to take place - skin becomes tanned by the sun , and fruit ripened . The most important feature of light for the purposes of photography . however , is that it travels in straight lines . You can see this for yourself if you observe the straight shadows formed behind objects that block light from the sun or watch rays of sunlight passing through smoke .
The behavior of light varies according to the material or surface it strikes . Opaque materials such as wood or metal block the passage of light by absorbing most of its rays . Transparent materials such as glass or water transmit light , allowing it to pass through . Textured surfaces scatter light in all directions as they reflect it , so that the light is softened and " diffused " . Clear smooth surfaces , like polished metal or glass , return the light waves without much scattering , so that you can see reflected mirror images . Most surfaces reflect some light rays back - the paler the surface , the more light it reflects . Black surfaces reflect no light , while white surfaces reflect almost all the light rays .
Light is also the source of all colors . It is composed of waves of different lengths ( called wavelengths ) , some of which are visible to the human eye and are perceived as different colors - long wavelengths as red , short wavelengths as blue - violet . The sun , as well as most other light sources , radiates a continuous spectrum of all these wavelengths , which we see as " white " " light . But objects around us absorb some wavelengths and reflect others . A ripe tomato , for example , absorbs most of the green and blue wavelengths but reflects red light , so you see it as red .
Transparent materials transmit all wavelengths equally unless they are colored . For instance , a blue stained glass window or color filter transmits blue light and absorbs all other wavelengths . Similarly , a red filter allows only red light to pass through . absorbing other wavelengths . This selective transmission is very important in photography . In black and white photography it affects the way tones reproduce , suppressing some , intensifying others ( see p . 100 ) . In color photography it is essential to the way that negative and slide film reproduce colors and to color processing and printing ( see pp . 141-3 , 162-3 ) .
Light determines the way you perceive the shape and form of objects . For example , a tomato side - lit by the sun reflects red light strongly on the lit side . Light strikes its curved surface at different angles and is therefore reflected back to your eye at different intensities . Your eyes and brain recognize that these gradations of brightness signify " roundness " without your having to touch the tomato to find out .
However , you can only see the objects around you clearly because your eyes admit only a restricted amount of light ( through a minute hole - the pupil , see page 20 ) which is then focused by the lens of the eye .
Light , lenses , and forming images
The principle of admitting light through a minute hole in order to produce a reflected image has been known since ancient times- it is the principle of the pinhole camera or " camera obscura " .
The explanation of this phenomenon is quite simple . As light travels in straight lines , light rays from the top part of the scene outdoors can only reach the bottom part of the receiving area through the pinhole , and vice versa , creating an inverted image of brighter and dimmer reflections . An image produced in this way is rather dim and ill - defined , because the hole is very small and light rays travelling from each point of the subject are slightly dispersed as they pass through the hole .
To produce a brighter and sharper image it is necessary to gather more light , and converge the light rays , that is , focus the image . This requires a lens .
When a light ray enters a transmitting material , such as glass , at an oblique angle , it is bent or " refracted " . You can see this if you put a spoon in a glass of water - from certain angles the spoon appears bent . If you make a disk of glass with curved surfaces ground thinner at the edges that at the center , you can use the principles of refraction to converge the light rays so that they meet together at one point . This is the principle on which the converging lens is based .
A converging lens transmits light rays from each part of the subject and brings them to focus on a flat surface ( such as paper or film ) . Light rays from the top and bottom , left and right parts of the subject are brought to focus on diametrically opposite parts of the receiving surface . This produces a sharp and detailed image of the subject , upside - down .
The converging lens was added to the " camera obscura " as early as the sixteenth century . It took another three hundred years to find a way of recording the image , as explained overleaf .
The qualities of light :
Light travels in straight lines The lit side of a tomato absorbs most of the light and reflects the remainder . Because light travels in straight lines , the area behind the tomato does not receive any light and a shadow is formed . Light , as a form of energy , also helps the tomato to grow and ripen .
Light can be bent When directed at an oblique angle through a glass prism the light is bent an effect known as refraction . This is because light travels more slowly through glass than through air .
Light can be reflected Different types of surfaces reflect different amounts of light . A smooth polished surface , such as a mirror , reflects most of the light reaching it . redirecting the beam . The two angles made by the light beam to the flat surface are equal .
Light can be diffused Light passed through a translucent material , such as clouds or tracing paper , is scattered in all directions . Light reflected from mat or textured opaque surfaces is also diffused . Scattered light forms less distinct , graduated shadows .
Light contains colors Light is composed of waves of different lengths ( called wave- lengths ) . Each wavelength is a particular color . The whole spectrum of colors is contained in light which appears white you can see the colors separated out naturally in a rainbow , or when light is directed at an oblique angle through a prism . Colored objects appear colored because they reflect certain wavelengths and absorb others .
Pinhole image You can form a crude image by admitting light from a brightly lit scene through a tiny hole into a dark box or room . On the surface furthest from the hole an inverted image of the scene will be visible . This is because light from the top part of the scene can only reach the bottom part of the receiving surface through the small hole , and vice versa . Details in the image are never quite sharp because the light is not bent to a point of focus but simply restricted to a narrow beam the size of the hole .
Making a pinhole image You can produce a pinhole image by using a short tube with a piece of tracing paper at one end and an opaque material with a tiny hole in the center at the other . If you hold this in a dark corner of a room with the pinhole pointing toward a brightly lit object , an inverted image will be formed on the tracing paper .
Replacing a pinhole with a lens A light converging lens solves the problems of using a pinhole to form an image . It bends incoming light to points of focus , so that each part of the subject is rendered with great clarity . The lens must be accurately distanced from the receiving surface ( focused ) so that the surface coincides with the sharp image . A lens can also be much wider in diameter than the pinhole so that the image formed is much brighter and easier to see . Try making this change yourself , using a simple magnifying glass . In fact a magnifier still has many aberrations ( optical errors ) which distort image shape and detail .
Lens shapes Lenses which are made thicker in the center than at their edges converge light . If the center is ground thinner than the edges the lens has the opposite effect on light rays - it causes them to diverge . Weak diverging lenses are combined with strong converging types in cameras to help correct aberrations in the image . The amount by which a lens converges or diverges light depends upon its thickness , and the type of glass from which it is made .
How lenses work
Refraction When passed through a block of glass , such as shown left , light rays are refracted and bent .
Converging light If two prisms are placed base to base light rays are refracted so that they bend toward each other and converge . This is the principle of the converging lens , above left , a lens used in all cameras . It is a disk of glass ground thinnest around the edges so that light rays from different directions are bent to focus on one point . A magnifying glass is a con- verging lens . It will bend the light from the sun on to a piece of paper . To form an image it must be held at a certain distance from the paper- known as the focal length of the lens .
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