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Special wide - angle lenses
We have seen that short focal length lenses give a wider angle of view , help increase perspective , and can give a greater depth of field than a 50 mm lens . These effects are amplified by very short focal length lenses .
One of the most obvious characteristics of very short focal length lenses is the increased angle of view they give . An 18 mm lens , for example , has about a 94 ° angle of view . The wider angle of view results in image distor- tion straight lines can appear curved and curved lines straight . Lenses can be built to correct this distortion , but with focal lengths shorter than about 17 mm it is increasingly difficult to make a linear corrected lens .
Using very short focal length lenses makes objects appear to diminish rapidly in size with distance . This creates an exag- gerated sense of perspective - objects which are quite close appear far apart .
The depth of field on short focal length lenses is very great . Fisheye lenses often give a depth of field that extends from only a few inches away from the lens to infinity , so that focusing is not necessary .
Very short focal length lenses are not positioned at their real focal length from the film . Instead , many modern lenses are of an inverted telephoto design which enables the lens to be positioned further away from the film while maintaining the charac- teristics of its short focal length .
Shift lenses are a special type of wide- angle lens . They enable you to correct linear distortions produced when working close - up to tall or long subjects .
Wide - angle lenses
Three types of wide - angle lenses are shown left . The 8 mm fisheye lens , far left , is not corrected for linear distortion and produces a circular image in which most straight lines appear curved . Filtering is done by a disk in the lens barrel . The center , 21 mm lens is corrected for this linear distortion as with a standard lens , lines parallel to the picture plane appear straight . The 35 mm shift lens , near left , can be moved on the camera around its normal position to control per- spective as explained below .
8 mm fisheye lens
21 mm rectilinear lens
35 mm shift lens
Wide - angle lenses and distortion
The picture , right , was taken with a 21 mm wide - angle lens from a close - up position . This close view- point , plus the image stretch created by the lens gives noticeable distortion of shape and scale . Com- pare , for example , the size of the girl's nearest hand to her head .
Shift lens
Some wide - angle lenses have shift mounts , shown below , to control perspective . Normally , when photo- graphing tall subjects , such as the building , right , you have to tilt the camera upward to fit them into the picture frame . As shown near right this makes vertical lines appear to converge . With a shift lens you can correct this by keeping the camera vertical . Instead you displace the lens to take in the subject , so that vertical lines appear normally , far right .
A short focus lens positioned near to the film elongates shapes furth- est from the lens center . Although modern inverted telephoto designs reduce this distortion you should try to place your main subject near to the center of your picture to minimize the effect .
Wide - angles and linear distortion
As the focal length becomes short- er and angle of view greater on a lens , it is increasingly difficult to maintain a normal rectilinear image ( straight lines recording without bending ) . " Corrected " lenses with an angle of view of over 100 ° begin to distort the image more than if they were not corrected and allowed the lines to curve . This is where fisheye lenses differ from wide - angle lenses . They do not attempt to correct the image . Fisheyes are extreme wide - angles in which image detail rapidly becomes smaller , and straight lines be- come increasingly curved at the edges of the picture . With fisheye lenses angles of view of 220 ° are possible , giving circular images within the film frame . A less extreme 180 ° fisheye fills the whole 24 x 36 mm frame .
15 mm rectilinear lens
The picture , left , was taken from about 2 ft ( 0.6 m ) in front of the auto- mobile radiator grill using an extreme wide - angle lens . Despite the very short focal length , the lens has normal rectilinear corrections so the lines in the image appear straight and there is no obvious distortion . The width of the car is emphasized by the steep perspective created by the close viewpoint and the wide angle of view .
16 mm fisheye lens
The picture , left , was taken using a 16 mm fisheye lens from the same viewpoint as the picture above . The short focal length gives approxi- mately the same angle of view but the image is distorted . This is because it has been magnified by different amounts across the frame . The central area , for example , has been enlarged and edge details reduced .
Fisheye construction
The diagram above shows the complex arrangement of lenses in- side an 8 mm fisheye lens . Two large diverging collector elements at the front of the lens give it an 180 ° angle of view .
Fisheyes need many more ele- ments than standard or long focus lenses . The glass shapes are difficult to grind and assemble accurately . This means that good fisheyes are expensive , and cheap types often give poor image quality .
Fisheye converters
A fisheye converter is much cheap- er than a complete fisheye lens but has the same effect on the image . It consists of a deeply curved lens which attaches over your standard lens , top right . The best results are achieved when the lens aperture is smallest .
A bird's eye attachment , bottom right , also gives a fisheye effect . It consists of a convex mirror at one end of a glass tube , which fits over your standard lens . The reflecting mirror always shows the camera and the photographer at the center of the image .
Fisheye converter
Bird's eye attachment
8 mm fisheye lens
An extremely short focal length , 8 mm fisheye lens gives a startling 220 ° angle of view , shown in the picture above . For this high jump shot the camera was positioned facing upward directly below the bar and fired by a long cable release .
Even the roof of the stadium is included by the wide angle of view .
Special wide - angle lenses
We have seen that short focal length lenses give a wider angle of view , help increase perspective , and can give a greater depth of field than a 50 mm lens . These effects are amplified by very short focal length lenses .
One of the most obvious characteristics of very short focal length lenses is the increased angle of view they give . An 18 mm lens , for example , has about a 94 ° angle of view . The wider angle of view results in image distor- tion straight lines can appear curved and curved lines straight . Lenses can be built to correct this distortion , but with focal lengths shorter than about 17 mm it is increasingly difficult to make a linear corrected lens .
Using very short focal length lenses makes objects appear to diminish rapidly in size with distance . This creates an exag- gerated sense of perspective - objects which are quite close appear far apart .
The depth of field on short focal length lenses is very great . Fisheye lenses often give a depth of field that extends from only a few inches away from the lens to infinity , so that focusing is not necessary .
Very short focal length lenses are not positioned at their real focal length from the film . Instead , many modern lenses are of an inverted telephoto design which enables the lens to be positioned further away from the film while maintaining the charac- teristics of its short focal length .
Shift lenses are a special type of wide- angle lens . They enable you to correct linear distortions produced when working close - up to tall or long subjects .
Wide - angle lenses
Three types of wide - angle lenses are shown left . The 8 mm fisheye lens , far left , is not corrected for linear distortion and produces a circular image in which most straight lines appear curved . Filtering is done by a disk in the lens barrel . The center , 21 mm lens is corrected for this linear distortion as with a standard lens , lines parallel to the picture plane appear straight . The 35 mm shift lens , near left , can be moved on the camera around its normal position to control per- spective as explained below .
8 mm fisheye lens
21 mm rectilinear lens
35 mm shift lens
Wide - angle lenses and distortion
The picture , right , was taken with a 21 mm wide - angle lens from a close - up position . This close view- point , plus the image stretch created by the lens gives noticeable distortion of shape and scale . Com- pare , for example , the size of the girl's nearest hand to her head .
Shift lens
Some wide - angle lenses have shift mounts , shown below , to control perspective . Normally , when photo- graphing tall subjects , such as the building , right , you have to tilt the camera upward to fit them into the picture frame . As shown near right this makes vertical lines appear to converge . With a shift lens you can correct this by keeping the camera vertical . Instead you displace the lens to take in the subject , so that vertical lines appear normally , far right .
A short focus lens positioned near to the film elongates shapes furth- est from the lens center . Although modern inverted telephoto designs reduce this distortion you should try to place your main subject near to the center of your picture to minimize the effect .
Wide - angles and linear distortion
As the focal length becomes short- er and angle of view greater on a lens , it is increasingly difficult to maintain a normal rectilinear image ( straight lines recording without bending ) . " Corrected " lenses with an angle of view of over 100 ° begin to distort the image more than if they were not corrected and allowed the lines to curve . This is where fisheye lenses differ from wide - angle lenses . They do not attempt to correct the image . Fisheyes are extreme wide - angles in which image detail rapidly becomes smaller , and straight lines be- come increasingly curved at the edges of the picture . With fisheye lenses angles of view of 220 ° are possible , giving circular images within the film frame . A less extreme 180 ° fisheye fills the whole 24 x 36 mm frame .
15 mm rectilinear lens
The picture , left , was taken from about 2 ft ( 0.6 m ) in front of the auto- mobile radiator grill using an extreme wide - angle lens . Despite the very short focal length , the lens has normal rectilinear corrections so the lines in the image appear straight and there is no obvious distortion . The width of the car is emphasized by the steep perspective created by the close viewpoint and the wide angle of view .
16 mm fisheye lens
The picture , left , was taken using a 16 mm fisheye lens from the same viewpoint as the picture above . The short focal length gives approxi- mately the same angle of view but the image is distorted . This is because it has been magnified by different amounts across the frame . The central area , for example , has been enlarged and edge details reduced .
Fisheye construction
The diagram above shows the complex arrangement of lenses in- side an 8 mm fisheye lens . Two large diverging collector elements at the front of the lens give it an 180 ° angle of view .
Fisheyes need many more ele- ments than standard or long focus lenses . The glass shapes are difficult to grind and assemble accurately . This means that good fisheyes are expensive , and cheap types often give poor image quality .
Fisheye converters
A fisheye converter is much cheap- er than a complete fisheye lens but has the same effect on the image . It consists of a deeply curved lens which attaches over your standard lens , top right . The best results are achieved when the lens aperture is smallest .
A bird's eye attachment , bottom right , also gives a fisheye effect . It consists of a convex mirror at one end of a glass tube , which fits over your standard lens . The reflecting mirror always shows the camera and the photographer at the center of the image .
Fisheye converter
Bird's eye attachment
8 mm fisheye lens
An extremely short focal length , 8 mm fisheye lens gives a startling 220 ° angle of view , shown in the picture above . For this high jump shot the camera was positioned facing upward directly below the bar and fired by a long cable release .
Even the roof of the stadium is included by the wide angle of view .
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