[keith_d]

One final piece is the maximum flash sync speed.

The light output from a flash can last anything from 1/10000 of a second to 1/1000 of a second depending on the power and design.

But, most film cameras will give odd results if you set the shutter speed to 1/1000. This is because the shutter is made up of two parts (like roller blinds). The first blind uncovers the film to expose it to light, and the second follows behind it to block the light again. So effectively you have a moving slit passing across the film. To get a 1/1000 of a second exposure, the second curtain will start covering up the film before the first has reached the other side. So whenever the flash fires part of the film will be covered by one of the blinds.

With modern digital cameras things are a little different because they use electronics to activate the sensor instead of moving blinds. But at high shutter speeds you still get poor overlap between the sensor activation and when the flash is producing maximum light. This tends to mean rather erratic exposure.

Nikon does have a workaround for this, which means firing the flash for a longer period to ensure better overlap. But I'm not a big fan since it means reducing the amount of light from the flash.

As a general rule, I avoid shutter speeds above 1/250 when shooting with a flash and usually keep to 1/125 or slower.