Flash and shutter speed


TPF Noob!
Oct 12, 2007
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Gilberts, IL
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For some reason I can't go faster than 1/200 with my build in or external flash. Nikon D80, SB-800,Nikkor 18-55mm f/3.5-5.6 - manual mode. Am I doing something wrong? I'm not sure where to go from here.

I'm not familiar with the D80 but I think that if you check the manual you will find that 1/200th sec is the fastest shutter speed that will synchronise with the flash. Any faster speed would result in partial exposure of the frame.
You should be able to use the SB-800 (and SB-600) at up to 1/4000 in Auto-FP mode, which is a custom setting on the D80, I think. Custom setting 25.

To help understand the Why of shutter sync, we need to understand how a focal plane shutter works. These shutters either work horizontally, or vertically. Side to side, or top to bottom. Since vertical shutters have a shorter distance to travel, they can sync. faster. Early Horz. shutters had a typical max. sync. speed of about 1/60th sec. When a shutter has been tripped, it is at rest with its two half's, a top half and bottom half resting at the bottom. When it is wound both half's are moved to the top without any separation between the two. When the release is pushed, the bottom half shoots to the bottom, the exposure time required passes, and the top half drops to the bottom seling the light from the sensor. Here is where max. sync. comes into play. At max.sync speed, the bottom half has just reached the bottom, before the top half follows to meet it. At speeds faster than max. sync. before the bottom curtain reaches the bottom, the top half chases it to it's resting point. As speeds increase, the gap between top and bottom curtains become smaller and small until a small slit is all that is exposed to the sensor/film plane at any one time. It averages the correct shutter speed across the entire plane.
So, the max. sync. speed is dertimeden by the fastest shutter speed that both curtains are fully open to the sensor at the instant the flash is discharged. Lighter materials and other advancements have allowed the shutter curtains to move much faster. This has resulted in higher max. shutter speeds, faster frame rates, as well as higher max. flash sync. speeds.
I added a rudimentary diagram to the thread that Mike gave the link to. It shows roughly what John describes.

Thanks for the explanation - now I know:)

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