High Speed Sync Part I
In this article I will begin a discussion on killing ambient light using, among other things, High Speed Sync.
To start off, please watch the following video as it is a great visual aid on shutter operation and sync speed.
After the mirror flips out of the way, the first curtain of the shutter activates to begin exposing the sensor. Notice that the frame is completely open at this point. Then, after a moment, the second curtain activates to end the exposure.
This means that the shutter speed had to have been at 1/200 or below. Anything over 1/200 you would have seen the second curtain start to fall before the first curtain was all the way down. In fact, at speeds of 1/1000 and over they start coming down almost at the same time, the first curtain starts to fall and is almost immediately followed by the second, leaving open only a tiny slit to expose the frame.
A typical small flash’s bust of light only lasts only about 1/10,000th of a second. If the shutter is never fully open as in the case of shutter speeds over 1/200, part of the frame will always be blocked by that second curtain racing down after the first. This causes part of your frame to miss out on that very fast burst of light, leaving a section of your image underexposed. This is often referred to as “black-banding” or “black bars” That’s why we say that 1/2o0 is the “Max Sync Speed” for Canon (1/250 for Nikon). It’s the fastest your shutter can be and still have the frame completely open, if only for an instant.
Camera manufacturers have offered a solution to this limitation called High Speed Sync, in a later post I will discuss the pro’s and con’s of High Speed Sync and offer some workarounds to the limitations of non-HSS flashes/triggers.
The Napa Photographer