The Variable Shutter
On cameras equipped with a variable shutter,the shutter angle can be narrowed to change shutter speed. Some bariable shutters may be shut dowm continuously, while others can only be shut down to certain angles.
Narrowing the angle reduces shutter speed. A 90'shutter ,for example ,gives a shutter spee of about1/100 at 24FPS (using the above formula for shutter speed).Closing the shutter reduces the exposure, allowing high-speed film to be used outdoors or allowing the lens to be opened to decrease depth of field or shooting at a selected f-stop.
A variable shutter that can be closed down while the camera is running allows exposure changes in the middle of a shot .For example,when the camera moves from a sunlit to a shaded area within a shot ,it is often necessary to change exposure. The iris diaphragm of the lens can be changed,but this would change the depth of field and may be more noticeable than shutting down the variable shutter .If the variable shutter can be shut down continuously to 0 degree with the camera running, in-camera fades and dissolves can be created.
Strobing ro Skipping
Decreasing the shutter angle makes the exposure for each frame shorter and freezes motion more effectively.The increased sharpness of each frame is advantageous for making still enlargemets from movie frames and for motion analysis but often causes unwanted effects in the moving image .Strobing or skipping may occur when there is any camera or subject movement .If the movement is too fast,the eye is not able to integrate successive frames and the image seems to skip rather than move continuously,causing the viewer eye strain .Skipping most often appears in pans,especially pans across strong vertical lines .The higher the image contrast or greater the image sharpness,the more likely that strobing will occur.Fast shutter speeds also increase the likelihood of strobing. In general,it is safer not to close down the shutter for exposure control if there is any camera or subject movement.
A phenomenon related to strobing,and frequently referred to by the same term ,is often noticed when the wheels of a moving vehicle on the screen seem to be stopped or to be traveling in reverse.This occurs when the intermittent exposures happen to catch spokes at the same position in consecutive frames (thus,the wheels seem stopped)or catch them in a position that causes the wheels to appear to be spinning in reverse.
On cameras with a variable shutter ,always check that the shutter is open before every day's shooting .if someone else has used the camera, the shutter opening may have been narrowed .some cameras have devices to warn you that the shutter has been closed on others,like the Éclair NPR,you must rotate the turret to check the position of the shutter.
要自己翻译的哦
比较多一点
就剩50多了
比较长 辛苦了
最近我会努力赚点分 然后追加的
谢谢
补充一下~!!不要软件翻译的哦`!!!