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الخطوة 2: المرشحات .. معدات وتقنيات إضافية .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
STEP 2 : FILTERS
Colored filters modify the ways colors record Without filters , black and white panchro- matic films turn colors into gray tones which roughly correspond to the tonal range we normally see . Adding colored filters selectively lightens or darkens these tones . In color photography , filters are used to correct or to distort color balance . This will be discussed on page 156 .
Colored filters
A colored filter lightens the reproduction of all colors that match its own color , and darkens complementary colors ( see p . 148 ) . White , black , and neutral grays in the subject are not affected . You can always preview the effect of a particular colored filter by holding it to your eye and noting the way it affects subject colors .
Filters can be bought as glass disks , or can be cut out of thin gelatin film . Both fit into holders which screw or push on to the front of your lenses . Alternatively , you can buy filters which are ready mounted into holders . Their position on the front of the lens creates difficulties with extreme wide- angle lenses because the holder itself may cut into the field of view . Most " fisheyes " ( see pp . 96-7 ) house filters within the lens barrel and you just dial in as required . Most mirror lenses ( see p . 99 ) can take filters between the lens and camera body .
Because the dye in colored filters reduces the amount of light that passes through the lens , you have to compensate with a longer exposure . With a through - the - lens meter this is not necessary because it reads the amount of light passing through the lens . But with other types of metering you must multiply the exposure by the filter factor recommended by the manufacturer .
Ultra - violet filters
Normal black and white ( and color ) film responds to ultra - violet light . This light is invisible to our eyes , but in distand land- scapes or at high altitudes it makes the scene record much paler . The effect of this - aerial perspective is shown on page 115 . It can be eliminated by using an ultra - violet UV ) filter . This filter is clear and needs no extra exposure , but it removes the ultra- violet light scattered by the atmosphere . It is also used in color photography ( see p . 147 ) .
Filtering for blue skies
The picture below was taken through an orange ( x3 ) filter which intensifies its complemen- tary color- blue . The sky is very dark , providing great contrast with the white clouds .
No filter
The subject below was photo graphed on normal , panchro matic film . In the picture the tones of the various fruits and vegetables are approximately the same as they appear to the eye . The tomato . cucumber , and parsley are dark : the apple . bananas , and lemon are light . The overcast sky reproduces light gray . Adding a color filter lightens objects of its own color and darkens its complementary colors .
Red filter
Through a x6 red filter . below . most green and blue light is ab- sorbed , and these colors are dark in the picture . Reds , such as the tomato appear white .
Green filter
The x4 green filter used for the picture below absorbs most red and blue light . darkening those colors . Greens are made lighter .
Starburst filter
The picture , right , was taken through a starburst attachment . shown below . This is a molded glass filter marked with a grid of crossed lines . It has the effect of elongating highlights , and so is most useful with subjects contain- ing bright light sources or reflec- tions . An SLR camera allows you to check the exact position of the star " rays " . As you rotate the filter . the spread line of each highlight rotates . Its width increases as the lens aperture is reduced .
You can create other spread effects or general diffusion of detail by Using a UV or similar clear filter , and smearing its surface with clear grease . This produces a hazy image . If you comb the grease into lines . it spreads the light in one or more directions . You should never do this on the lens surface .
Polarizing
A polarizing filter reduces un- wanted reflections from surfaces such as glass or water . In the near right picture reflection interferes with the main subject . With a polarizing filter . far right , the reflection is eliminated .
How polarizing filters work
Ordinary light vibrates in all direc- tions : polarized light - reflections from non - metal surfaces or from some parts of a clear blue sky- vibrates in one plane only . A polarizing filter works by blocking the light in one plane , as shown below . The filter can be rotated in its mount , as shown above . When this disk is at right angles to the plane of polarization the unwanted light is reduced .
Neutral density filters
Neutral density filters reduce the intensity of light but do not affect tonal range . The picture above was taken with a small aperture and fast shutter speed . With a neutral density filter added , right , the aperture could be increased so that the depth of field is reduced and only the main subject is sharp .
STEP 2 : FILTERS
Colored filters modify the ways colors record Without filters , black and white panchro- matic films turn colors into gray tones which roughly correspond to the tonal range we normally see . Adding colored filters selectively lightens or darkens these tones . In color photography , filters are used to correct or to distort color balance . This will be discussed on page 156 .
Colored filters
A colored filter lightens the reproduction of all colors that match its own color , and darkens complementary colors ( see p . 148 ) . White , black , and neutral grays in the subject are not affected . You can always preview the effect of a particular colored filter by holding it to your eye and noting the way it affects subject colors .
Filters can be bought as glass disks , or can be cut out of thin gelatin film . Both fit into holders which screw or push on to the front of your lenses . Alternatively , you can buy filters which are ready mounted into holders . Their position on the front of the lens creates difficulties with extreme wide- angle lenses because the holder itself may cut into the field of view . Most " fisheyes " ( see pp . 96-7 ) house filters within the lens barrel and you just dial in as required . Most mirror lenses ( see p . 99 ) can take filters between the lens and camera body .
Because the dye in colored filters reduces the amount of light that passes through the lens , you have to compensate with a longer exposure . With a through - the - lens meter this is not necessary because it reads the amount of light passing through the lens . But with other types of metering you must multiply the exposure by the filter factor recommended by the manufacturer .
Ultra - violet filters
Normal black and white ( and color ) film responds to ultra - violet light . This light is invisible to our eyes , but in distand land- scapes or at high altitudes it makes the scene record much paler . The effect of this - aerial perspective is shown on page 115 . It can be eliminated by using an ultra - violet UV ) filter . This filter is clear and needs no extra exposure , but it removes the ultra- violet light scattered by the atmosphere . It is also used in color photography ( see p . 147 ) .
Filtering for blue skies
The picture below was taken through an orange ( x3 ) filter which intensifies its complemen- tary color- blue . The sky is very dark , providing great contrast with the white clouds .
No filter
The subject below was photo graphed on normal , panchro matic film . In the picture the tones of the various fruits and vegetables are approximately the same as they appear to the eye . The tomato . cucumber , and parsley are dark : the apple . bananas , and lemon are light . The overcast sky reproduces light gray . Adding a color filter lightens objects of its own color and darkens its complementary colors .
Red filter
Through a x6 red filter . below . most green and blue light is ab- sorbed , and these colors are dark in the picture . Reds , such as the tomato appear white .
Green filter
The x4 green filter used for the picture below absorbs most red and blue light . darkening those colors . Greens are made lighter .
Starburst filter
The picture , right , was taken through a starburst attachment . shown below . This is a molded glass filter marked with a grid of crossed lines . It has the effect of elongating highlights , and so is most useful with subjects contain- ing bright light sources or reflec- tions . An SLR camera allows you to check the exact position of the star " rays " . As you rotate the filter . the spread line of each highlight rotates . Its width increases as the lens aperture is reduced .
You can create other spread effects or general diffusion of detail by Using a UV or similar clear filter , and smearing its surface with clear grease . This produces a hazy image . If you comb the grease into lines . it spreads the light in one or more directions . You should never do this on the lens surface .
Polarizing
A polarizing filter reduces un- wanted reflections from surfaces such as glass or water . In the near right picture reflection interferes with the main subject . With a polarizing filter . far right , the reflection is eliminated .
How polarizing filters work
Ordinary light vibrates in all direc- tions : polarized light - reflections from non - metal surfaces or from some parts of a clear blue sky- vibrates in one plane only . A polarizing filter works by blocking the light in one plane , as shown below . The filter can be rotated in its mount , as shown above . When this disk is at right angles to the plane of polarization the unwanted light is reduced .
Neutral density filters
Neutral density filters reduce the intensity of light but do not affect tonal range . The picture above was taken with a small aperture and fast shutter speed . With a neutral density filter added , right , the aperture could be increased so that the depth of field is reduced and only the main subject is sharp .
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