johnw@astroatc.UUCP (John F. Wardale) (01/21/89)
In article <1818@maccs.McMaster.CA> nusip@maccs.UUCP (Mike Borza) writes: >Pardon my ignorance, but... doesn't this mean that shutter speed is >essentially irrelevant for a flash picture taken using an electronic >flash? If so, how does one control the exposure? Yes! You can change F-stops on the lens. You can control the light-output from the strobe. Automatic strobes have *FAST* sensors that shut the strobe off when enuf light has come out. You can NOT control it in the time-domain. You must set your camera at or slower than it's "X" sync speed. [slower lets you blend in more of the available light. (3 stops down is better than 5 or 6) and it softens the lighting effect slightly] --------------------------------------------------------------------- The Rest of This Discussion *ASSUMES* a FLAT (ie FOCAL-PLANE) Shutter --------------------------------------------------------------------- Most cameras have X at one of {1/60 1/100 1/125} At speeds FASTER than the X sync, the the closing blade of the shutter starts closing *BEFORE* the opening blade completes its travel. This is fine for stoping action because each point [grain, pixel, region or ???] on the film is exposed for a shorter amount of time! For a shutter speed of 1/1000 (for an X @ 1/100 system) the shutter is a moving slot, 1/10th the width of travel *YES, if you *PAN* with a moving object you can extend or compress it with these "apparently fast" shutter speeds. NOTE: Some shutters move hoizontally, some move vertically. Watch *YOUR* shutter at 1/4 or slower with NO film, and NO lens. ------------------------------- On my camera If I use a strobe at 1/125 I get about 1/3 or 1/4 of the frame black. If *I* designed a camera, I would rig it to *NOT* fire the strobe when the shutter was set faster than the X speed. [Thus you'd ruin *ONE* frame, not the whole damn roll!!! :-( :-(] -- John Wardale ... {seismo | harvard | rutgers | ames} ! {uwvax | cs.wisc.edu} ! astroatc!johnw or astroatc!johnw@cs.wisc.edu To err is human, to really foul up world news requires the net!