Flash can be intimidating to new photographers. At best, it’s an unnatural-looking light source, and at worst it destroys the image entirely. Or is it?
Flash can actually be one of the most useful tools in photography. It’s essential for many different types of shots. Unfortunately, it’s also one of the most misunderstood tools in photography. Yes, a flash can look unnatural. Yes, a flash can produce funky shadows. But if your flash is obvious in your image, or adds harsh shadows, you’re doing it wrong. Flash is an amazing tool if you know how to use it.
There are many different elements to consider when using a flash, but part of reigning in that flash and actually using it to make your images better (and not worse) is to understand flash sync and flash sync modes.
What is flash sync?
For the flash to light the image, it has to synchronise with the camera’s shutter, otherwise, the flash won’t fire at the same time the image is being taken. “Sync” is simply short for synchronization. On the default flash mode, the flash is synced to go off for the duration of the image.
Flashes can’t fire as quickly as cameras can snap a photo, however. The term flash sync is used inside a camera’s technical specifications to indicate the highest shutter speed that can be used with a flash. On most DSLRs, the flash sync is about 1/200 or 1/250.
What happens if you use a shutter speed over 1/250 with a flash? In most modes, the camera won’t let you adjust the settings any higher than that with the flash on, but manual mode is an exception. If you use a shutter speed higher than the flash sync speed in manual mode, you’ll wind up with a black band across the bottom of your image. This is from how the shutter curtain works. Suffice it to say, you don’t want to use a shutter speed over your camera’s maximum flash sync speed, or part of the photo will be black.
Some flash heads have high speed synch flash. This type of flash is actually a series of bursts of light that allow you to use shutter speeds over that maximum flash sync speed. This is dependent on the type of flash you buy, not on your camera body.
What are flash modes?
The term flash sync is also often used to describe different flash modes. The default flash mode fires the flash at the beginning of the shot. In other words, the flash is synced to go off at the beginning of the shot. But, not every flash mode fires this way.
Rear curtain sync:
A rear curtain sync will fire the flash at the end of the exposure, instead of at the beginning. Why is this important? First, you have to understand a bit how flash helps to freeze motion.
Say you are taking a long exposure of a moving object. The flash will actually combat some of the motion blur, or help to freeze the subject. Even if your subject is moving during the entire exposure, the subject will appear much clearer while the flash is firing.
Since you are using a slow shutter speed, the flash is only going to fire for part of the exposure. Under the normal mode, the flash will fire at the beginning, freezing the subject in place at that moment, but