How fast can the shutter on a camera actually move? There is a limit to how fast blind can open and shut physically. There are ways around this, which is what camera manufacturing companies have worked out. However, the photographer must keep this in mind when taking high speed photographs because the light must flash at the precise split second that the shutter is open or the light is useless.
Photographers early on realized that the light from burning magnesium allowed them to cut exposure times exponentially. Prior to flash powder, subjects had to remain motionless for lengthy periods in order for the photograph to be clear and crisp. However, intense light helped to make the exposure clear faster and (although very dangerous) this was much preferable then hoping the subject, camera, etc didn’t move.
When I was a boy, I can remember flash cubes. It was an innovation on cameras that allowed the flash to be changed “automatically”. A cube with a flash on each side was attached to the top of the camera body. When the film was wound the cube would spin. Fantastic! Eventually batteries allowed cameras to have an internal flash (which is what we are used to today).
However, regardless of where the flash comes from, it must be timed with the shutter opening or the light is wasted. To help visualize this picture in your mind what actually happens when you press the button to take the photo: the mirror flips up, the aperture stops down, the first shutter/blind opens, and the second blind follows. The time between the first and second blind is the exposure.
Because of simple physics, the blind cannot move any faster than about 1000th of a second (normally indicated by a red number or X. However, blinds are often mounted vertically now instead of horizontally because it can travel just a little faster that way. But regardless of the speed of the camera there is a time when the blind cannot travel any faster. To combat this and allow faster speeds, camera manufacturing companies have “solved” this by allowing the second blind to follow the first blind before the first blind finishes its trip across. This results in a narrow (rectangular) slit of exposure that travels across film instead of getting exposed all at once.
This is important because the flash (light being much faster) must be timed to sync with the opening of that slit or the flash is wasted. Most cameras allow this to happen automatically with a simple connection wire and an adjustment on the camera marked with a M/Fp and a X. The M or Fp marking allows for delayed flash; the X marking syncs the flash with the shutter.
The M/Fp marking (it differs depending on camera manufacturer) is a useful setting for dynamic photographs. Perhaps you have seen pictures of people moving where the exposure was long enough to allow for a purposeful blurring of motion. A delayed flash at the end of the exposure captures a crisp subject on top of that blurred movement (coming just before the second blind closes). A cool effect.
It also is good to remember that the lighting you see through the camera while focusing is not the amount of light that will enter the camera when it is stopped down to the aperture when the photo is taken. Using a light meter is helpful to ensure that the correct lighting is used. We also have been trained to take three photos of each object increasing and decreasing the shutter speed by twice and by half to ensure that the correct exposure of light is captured.
No comments:
Post a Comment