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التصوير الفوتوغرافي الحديث
تجهم الصور ..
تأثيرات العدسة بسبب وضع الكاميرا ..
المنظور ..
ANGLE OF VIEW
The angle of view of a lens in a camera is expressed in degrees . Most standard lenses have an angle of view of approximately 50 degrees . If the angle is appreciably greater than this , the lens is called a wide - angle lens . If the angle is appreciably less than 50 degrees , the lens is called a long - focus or telephoto lens . For any given picture size , the focal length of the lens determines the angle of view . The long focal length lens , therefore , has a narrower angle of view . This is another way of saying that a telephoto lens takes in a narrow angle . By the same reasoning , a wide angle lens necessarily has a short focal length . ( Figure 24 ) .
Fig . 24 How focal length of lens determines angle of view .
Whether a lens is considered short - focus ( wide angle ) or long - focus ( telephoto ) depends on the film size as well as the actual focal length . For example , a 75mm focal length is considered normal for a 24 x 24 camera . It would be long - focus for a 35mm camera , and short - focus for a 4 x 5. The best way to relate the focal length of the lens to the size of the picture it takes is to consider the angle of view . Let us see how this works .
In Figure 25 , a lens of 2 - inch focal length ( 50mm ) is shown projecting an image of a distant object . Since the lens focal length is 2 inches , the distance between the lens and the image is 2 inches . At that distance , the image size , let us say , is 1 inch in height . Now in Figure 26 , we see a 4 - inch lens set to photograph the same subject at the same distance . However , since the focal length of this lens is 4 inches , the image is 4 inches from the lens instead of 2 , and it is also twice as high . Thus , we can see that if we photograph the same object from the same distance using a camera with both a longer focal length lens and a larger film size , we would simply get a larger negative with exactly the same perspective and angle of view .
Suppose , however , we use a 4 - inch lens in the camera with the 1 - inch film size . This is shown in Figure 27. With this combination , at the same distances , we could only photograph half of the subject , so our angle of view is limited . In fact , it is only half of what it was with a 2 - inch lens . On the other hand , if we mounted our 4 - inch lens in a camera with a 4 - inch film size as shown in Figure 28 , our angle of view would be much greater . In this camera , the 4 - inch lens would be considered a wide angle lens . In the 1 - inch film size camera , of course , it would be considered a long - focus , or telephoto lens .
The best focal length for ordinary work is about as long as the diagonal of the film on which it is to be used . The following table gives the most commonly accepted focal lengths for general use for various negative sizes :
Negative Size - - - Lens Focal Length
1 x 1½ in . ( 35mm ) 50mm ( 2 - inches )
2 1/4 x 2 1/4 in . 75-80mm ( 3 - inches )
2 1/4 x 3 1/4 in . 100mm ( 4 - inches )
4 x 5 in . 127-165mm ( 5-6½ - inches )
5 x 7 in . 8½ - inches
8 x 10 in . 12½ - inches
It should be pointed out that we have spoken as though a 4 - inch lens will perform equally well as a telephoto , or wide - angle or normal lens . This has been done only to simplify our explanations . Actually , this would not be the case ,
since each lens application has its own special requirements and calls for somewhat different lens design .
Though we have covered them separately up to now , perspective and angle of view have a natural relationship . You get the most natural appearing per spective when the angle of view of the camera is about 40 to 50 degrees . The reason is that with this angle photograph your subject from a distance which produces the most natural perspective .
تجهم الصور ..
تأثيرات العدسة بسبب وضع الكاميرا ..
المنظور ..
ANGLE OF VIEW
The angle of view of a lens in a camera is expressed in degrees . Most standard lenses have an angle of view of approximately 50 degrees . If the angle is appreciably greater than this , the lens is called a wide - angle lens . If the angle is appreciably less than 50 degrees , the lens is called a long - focus or telephoto lens . For any given picture size , the focal length of the lens determines the angle of view . The long focal length lens , therefore , has a narrower angle of view . This is another way of saying that a telephoto lens takes in a narrow angle . By the same reasoning , a wide angle lens necessarily has a short focal length . ( Figure 24 ) .
Fig . 24 How focal length of lens determines angle of view .
Whether a lens is considered short - focus ( wide angle ) or long - focus ( telephoto ) depends on the film size as well as the actual focal length . For example , a 75mm focal length is considered normal for a 24 x 24 camera . It would be long - focus for a 35mm camera , and short - focus for a 4 x 5. The best way to relate the focal length of the lens to the size of the picture it takes is to consider the angle of view . Let us see how this works .
In Figure 25 , a lens of 2 - inch focal length ( 50mm ) is shown projecting an image of a distant object . Since the lens focal length is 2 inches , the distance between the lens and the image is 2 inches . At that distance , the image size , let us say , is 1 inch in height . Now in Figure 26 , we see a 4 - inch lens set to photograph the same subject at the same distance . However , since the focal length of this lens is 4 inches , the image is 4 inches from the lens instead of 2 , and it is also twice as high . Thus , we can see that if we photograph the same object from the same distance using a camera with both a longer focal length lens and a larger film size , we would simply get a larger negative with exactly the same perspective and angle of view .
Suppose , however , we use a 4 - inch lens in the camera with the 1 - inch film size . This is shown in Figure 27. With this combination , at the same distances , we could only photograph half of the subject , so our angle of view is limited . In fact , it is only half of what it was with a 2 - inch lens . On the other hand , if we mounted our 4 - inch lens in a camera with a 4 - inch film size as shown in Figure 28 , our angle of view would be much greater . In this camera , the 4 - inch lens would be considered a wide angle lens . In the 1 - inch film size camera , of course , it would be considered a long - focus , or telephoto lens .
The best focal length for ordinary work is about as long as the diagonal of the film on which it is to be used . The following table gives the most commonly accepted focal lengths for general use for various negative sizes :
Negative Size - - - Lens Focal Length
1 x 1½ in . ( 35mm ) 50mm ( 2 - inches )
2 1/4 x 2 1/4 in . 75-80mm ( 3 - inches )
2 1/4 x 3 1/4 in . 100mm ( 4 - inches )
4 x 5 in . 127-165mm ( 5-6½ - inches )
5 x 7 in . 8½ - inches
8 x 10 in . 12½ - inches
It should be pointed out that we have spoken as though a 4 - inch lens will perform equally well as a telephoto , or wide - angle or normal lens . This has been done only to simplify our explanations . Actually , this would not be the case ,
since each lens application has its own special requirements and calls for somewhat different lens design .
Though we have covered them separately up to now , perspective and angle of view have a natural relationship . You get the most natural appearing per spective when the angle of view of the camera is about 40 to 50 degrees . The reason is that with this angle photograph your subject from a distance which produces the most natural perspective .
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