Re: OT: Digital Camers's
- From: "Rudeney" <rudeney@xxxxxxxxxxxxxx>
- Date: Tue, 4 Oct 2005 11:33:00 -0500
No wrote:
Yea, I have used the bulb trick for many a night time shot. I have a great picture from efiel tower of paris taken on bulb at night. Another neat trick, if you have a camera capable of a bulb setting, is one I did many years ago.
Set up your camera in complete darkness. Equip your flash, not mounted to the camera, with a sound trigger. These are easily contructed for a couple of $ with an SCR (Silicone controlled rectifier) and microhone from radio shack. See http://www.hiviz.com/tools/triggers/triggers2.htm for a schematic. The camera, on bulb, in complete darkness does not expose the film. The flash fires at about 1/100,000 of a second. The fast time of the flash will give you some incredible stop action photography without the need for a special high speed camera. See some interesting examples at http://www.hiviz.com/GALLERY/galleries.htm
Now THATS way off topic!
Many high-end SLR's can do this with the proper flash using high-speed sync mode and many even have some special features like front or rear curtain sync. The reason this works is that Most 35mm cameras actually control the shutter speed with a combination of the physical speed of opening the shutter as well as the aperture of the shutter (not to be confused with lens aperture). At high speeds, say over 1/200 of a second, instead of the shutter opening all at once and exposing the entire frame for the given duration, it actually opens as a slit which then moves across the surface of the film.
Imagine the shutter as a pair of drapes over a window. It would be very hard to fully open and then close the drapes in order to create an exposure of less than 1/10 of a second. However, instead of opening both sides of the drapes fully, then closing them very quickly, you slide the drapes all the way to one side of the window, then open them just enough to expose a slit of light, then quickly slide both drapes, maintaining the slit, across the window to the other side. If the slit is only 50% the size of the opening, the shutter speed is actually doubled. If the slit is only 10% of the opening, the shutter speed is multiplied by a factor of 10. This allows for some very high shutter speeds without having to build motors and actuators that actually move so quickly.
This moving curtain of a shutter also introduces some anomalies. On most cameras, the flash only illuminates the subject for a very brief time, in fact much less time than the shutter is actually open. At shutter speeds above about 1/200 of a second, the shutter is operating in the "curtain" mode. If the flash fires at the very beginning of the exposure, it may already be extinguished before the slit has moving across the entire film frame. This would result in part of the frame being properly exposed and the other part not. A high-speed sync capable flash and camera actually has the flash fire multiple times, in sync with the curtain movement, so that all parts of the frame are exposed. Because of this, most SLR cameras do not allow shutter speeds above 1/200 unless an HSS-compatible flash is being used.
Anyway, just some more OT photography tidbits!
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- RODNEY
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- From: Randy Berbaum
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