Attributes of common camera lens
CLZ Precision Optics Co., Ltd.    2016-07-25 06:27:08    文字:【】【】【

The farther the subjects is from the camera, the more likely it is to be compressed and deformed. In other words, the distance between the main body and the camera is not the factor which dominates the size of the image. If we use the telephoto lens, the main body would not be as small as it can be seen from our eyes. If we shoot with long lens in front of a group of runners, it will be easier to see the visual effect. The distance between these runners seems to be much more closer than the actual distance. Although they are running hard, it seems that there is no way forward. The reason of this visual effect is far-distance shooting with the use of the long lens.


 The Wide-angle lens can add the depth of pictures. The scenery can be seen Visually farther than the actual distance, while the subject is also reduced. When using a wide-angle lens, the distortion and deformation are unavoidable.  You may not like the distorted image caused by wide-angle lenses. In fact, this kind of perspective scale seems to be natural from the view near the top of the film. The closer the viewer is to the screen, the flatter you will feel about the two dimensional space effect. If you always sit in the front seats while watching a film, you may be able to fairly enjoy the visual effect that is compressed. On the contrary, if you always watch in the back seat, it’s probably because you like image with more sense of deepness.


Wide-angle lens can visually enlarge a small room. If a person is facing a camera, he or she would probably acts somewhat quickly and unnaturally. In general, the wide-angle lens will exaggerate any movement which goes towards or away from the camera. If we put the wide-angle lens in a moving vehicle and make it face to the front, the sense of speed and the scenery that moves backward can be fully emphasized. The wide-angle lens can also be used to emphasize the height of the image. For example, we can shoot something from the top of a tall building, or shoot a character from below.


Perspective scale of close-ups

 When doctoring a close-up of body parts above the shoulder with a wide-angle lens, it is necessary to pay special attention to the distance between the camera and the subject. As the deepness will be exaggerated, the nose will look too large, the ears look too small and seem to be moved afterward. This visual effect is often used in a comedy or some grotesque and absurd situations. When people move towards the camera, the nose becomes bigger and bigger. However, when people move laterally, it will not be out of shape and deformed.

 Usually, the camera and subjects are kept at a distance of 5 feet or more. In this case, there is no need to worry about any deformation of facial features. When doctoring the close-up of face, it’s necessary to avoid the feeling of flat (when shooting with a long lens in the long distance). If the image is without the stereo effect, its affinity will be reduced, which makes the viewer feel alienated. Although the perspective ratio will vary with the adjustment of the photographic distance, it is often unnoticed, unless there is extreme variation in the distance or the inner focal length of the lens.


The treatment of perspective ratio of documentary films


For a random documentary film, the control and adjustment of perspective ratio are less flexible. Photographic distance is determined by the convenience and comfort of staffs and the subject . The photographer use the applicable lens in general range of photographic distance to most possibly and ideally catch all the pictures. Take 16 cm as example, in 7 feet photographic distance, using the lens with the length of 10 to 50 cm can focus the facial features so that it can stand in the midddle ground. (using lens with length of 6 to 30 cm in the distance of 8cm ).


Lens and aperture

aperture-coefficient The lens will focus the reflected lights which come from the subject, and then project it onto the negative film. The function of gathering light is called "transmission of lens". It is usually expressed as aperture-coefficient (f-stop):


aperture-coefficient = inner focal length / diameter

aperture-coefficient shows how many lights passed through the lens. When the diameter is enlarged, the lights which pass through the lens will be increased. When the inner focal length is lengthened, the spread light in the lens is increased, while the lights which can make the negative plate more sensitive will be decreased. The better is the light transmittance, the more light is transmitted and vice versa.


Inside the lens is a mechanical device which is an iris diaphragm ( which is also aperture) . The device is composed of overlapped leaves, there is a hole in the center. The size of the hole can be controlled by closing the hole in the lens, so that the quantity of the light which pass into the lens can be controlled. This mechanical principle is quite similar to the pupil of the eye. To see clearly under the dim light, the pupil will automatically dilate to allow in more light; otherwise, when it is bright, the pupil will shrink to reduce the amount of light which passes in.


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