|Shutter speed real or imagined?|
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|A focal plane shutter has a divided curtain where each portion can move independently.
In the "FLASH" mode (when used in synchronization with a flash or strobe) the leading curtain must be fully open while the flash fires, then the trailing curtain closes.
Fast exposures are created by simultaneous movement, opening only a slit of light on the film (or ccd).
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|Some of the earliest models of digital cameras (early 1990's) did not have traditional shutters. They had a simple single speed mechanism like a door opening and closing, and the actually change in sensitivity was then created by changing the effective ASA of the ccd array on the fly. This proved to be a poor substitute for a true shutter.
Focal plane shutters are the standard shutters in many 35mm cameras and virtually all SLR cameras. Iris shutters (spring loaded mechanisms similar to an f-stop iris) are also around, but mostly in large format camera lenses.
There are also special opto-shutters that work by the application of a voltage to a solid state chip. They change a transparent ceramic from transmissive state to a light blocking state by altering the crystalline structure.
There are spring loaded blade shutters that work by passing a hole in an opaque material across the light path. There are numerous shutter designs and mechanisms that have been patented and used in cameras. They all function in the same general way, they limit or control the duration of light that hits the camera recoding media.
Shutter speed is used to balance the exposure, and usually selected for one of two purposes; to stop action (fast motion), or to reduce blur due to camera shake. There is very little that we will ever photograph in the macro mineral, jewelry, and gemstone world that will require "stop-action" photography Reducing camera shake and thus blur is, however, very important in close-up photography with the limited depth of field available.
Using a high shutter speed in conjunction with a high f-number is desirable but a real challenge in close-up photography Since the major reason for the high shutter speed is to reduce blur (due to camera shake) it is possible to compensate by using a tripod for most desktop work. A good tripod with an indirect shutter release mechanism provides better image quality at high f-numbers. ("Indirect shutter release mechanism" = camera self timer or remote shutter release.