Slow shutter speed Vs flash

k.udhay · Apr 15, 2013

O|||||||O said:
The flash duration wouldn't really be a factor in exposure, and the inverse square law wouldn't be any different than if we were talking about a desk lamp - the same rules apply, nothing special happens just because of the flash duration.

As far as shutter speed, that going to be whatever your camera is set to - BUT, if all of the exposure is from the flash, the flash duration effectively becomes the shutter speed. If you're really trying to freeze motion, use the lowest flash power you can get away with (TTL modes will tend to go with the highest power it can get away with).

My camera has a minimum shutter speed of 1/8000, and x-sync of 1/250... But my flash will blow that away if I can get the ISO high enough and the aperture large enough to allow me to use a very low power on my flash.

Thanks, Josh. During flash lit photographs at night outdoor with the subject slowly moving, I freeze the subject at the instant of flash. But, I also can see a thin blur on the border of the subject. Is it the image that was captured, during the non-flash duration? I am sorry if I am confusing more!

KmH · Apr 15, 2013

k.udhay said:
But, I also can see a thin blur on the border of the subject. Is it the image that was captured, during the non-flash duration? I am sorry if I am confusing more!

Yes. That 'border' is exposure from the ambient light.

Use a faster shutter speed to reduce the ambient light exposure. That may mean changing the ISO, lens aperture, or flash output power to maintain the same flash exposure, particularly if you're already at your camera's fastest flash x-sync speed.

pgriz · Apr 15, 2013

However, this two-exposures in one thing also opens up some creative possibilities. Let's assume you're shooting in a dim-enough setting that a proper exposure would be something like 1-2Seconds long. You're walking alongside your subject, and you handhold the camera even while it's on a very slow shutter speed. Set your flash sync to second curtain. Now walk alongside your subject, and pan the subject while shooting with a slow shutter speed. Your flash will fire at the end of the exposure. When you look at it, you will see the subject "frozen" by the flash, but "trailed" by the ambient light. Since you panned your subject, the amount of ambient blur on the subject will not be too great, but the background will be quite blurred with motion blur. Can't show it as I'm writing this while at work, but give it a try - its a form of light painting!