The Flash Sync-Speed

This episode is the first of the new series about Flash photography. Before even introducing a Flash in the equation, one needs to understand a fundamental aspect which is the Flash Sync-Speed… As we have seen in a very early episode about the camera’s Shutter, it is composed of 2 blades much like stage curtains. While old film cameras have their blades move horizontally, all new DSLR’s have them do vertically. As we discussed earlier, the Shutter speed is the time during which the sensor is exposed to the light, between the opening of the first curtain and the closing of the second. Let’s call those curtains: 1st curtain and 2nd curtain. Interestingly, for each camera, there is a Shutter speed beyond which the 2nd curtain (the closing one) starts moving before the 1st curtain (the opening one) has fully opened. The faster your Shutter speed is the narrower the time lapse between the opening and the closing of the 1st and 2nd curtain. Some DSLR like the Canon 60D I own enables me to reach 1/8000 sec. At that speed, the two curtains are following each other extremely closely.

What is the Flash Sync-Speed?

Well, it is very easy, one calls the Flash Sync-Speed, the Shutter speed beyond which the 2nd curtain start closing before the 1st curtain is fully open. On my Canon 60D, the FSS is 1/250 sec. Meaning that at 1/330 sec (1/250 sec + 1/3 stop) the 2nd curtain will start closing while the 1st curtain has not yet fully open. Why do we care? We care because if you were to fire a Flash beyond the FSS, this is what you would get:

Note, this is not possible to achieve in modern DSRL since the camera will not let you increase your Shutter speed beyond the FSS if it detects there is a Flash activated. I let you do a simple test, use the popup flash on your camera, and try to go at 1/300 sec. Unless you have a very expensive Medium format Hasselblad camera  (uses leaf shutter technology) or a simple, compact camera (does not have blades but an electronic shutter instead), your camera won’t let you reach that 1/300 sec speed.

Exception

While for the sake of approaching Flash photography we will keep in mind to use a Shutter speed lower or equal to the FSS, note that most modern DSLR cameras in combination with specific Flashes will enable you to shoot beyond the FSS, and I will cover this in another episode very soon so we do not get too confused here in our first lesson.