Figure 13-21: HSS Flash: A normal flash burst (the wider pulse in the left image) and the equivalent HSS output (right). The long pulse evenly illuminates the “traveling slit” used in High-speed Synch. Downside: you can only shoot close subjects.
How it works
Rather than waiting for the shutter to open all the way (or turn on electronically which your camera will do by default) before triggering the flash, the flash is told to output one long continuous flash whose intensity is right for the subject (as determined by the pre-flash). This long flash pulse illuminates the subject while the shutter’s “traveling slit” exposes a different part of the sensor.
It’s kind of like standing outside of a baseball park and looking at the game through a tiny little slit in the fence. You can’t see the whole scene at once, but you can move your head left and right and “see” the entire scene a small slit at a time. That’s how HSS works – as the shutter’s “slit” travels across the face of the sensor, the sensor is provided another thin strip of the scene. The HSS flash pulse is long enough to ensure that there’s the same amount of light on the subject when the slit is at the top of the frame and at the bottom.
Figure 13-21: HSS Flash: A normal flash burst (the wider pulse in the left image) and the equivalent HSS output (right). The long pulse evenly illuminates the “traveling slit” used in High-speed Synch. Downside: you can only shoot close subjects. |
Those of you who are technically inclined might be scratching your head, saying “Hey, I thought that Sony went with that electronic first shutter curtain thingy. Since the sensor is always fully open until the exposure ends, why is this ‘traveling slit’ stuff still relevant?” Good question. The answer is “the pixels are turned on one row at a time, starting at the top, at the same speed as what a physical shutter would have done”, thus enabling them to get the exact same kinds of high shutter speeds as with a conventional shutter.
There are some limitations to using HSS:
3 --> Flash Mode --> Rear sync.). (Why? The two ideas are incompatible. Rear sync applies when the shutter is completely open for a long period of time. That never happens when HSS is used.)
Figure 13-22: Even boring subjects can look dramatic using wireless flash. :-) |
If you’d like more inspiration on what wireless flash can do to give you awe-inspiring images, I highly recommend you spend some serious time at the website www.strobist.com. From their website: “Think of Strobist as a lighting idea bank, run by and for the most enthusiastic DSLR photographers. Our goal is to exchange ideas with other shooters and post many different lighting techniques - using real-world assignments as examples.”
I have also created other non-intimidating learning resources if you're interested in exploring this very important technique even more:
