I’m wholeheartedly opposed to being only a “Natural Light” photographer. I can’t imagine being limited to only working with the light available on hand. I have so much fun using strobes (which are the same as flashes) to light my work and help me create in any situation. However, there are some challenges to working with strobes, and the biggest one you need to understand is flash sync speed.
If your sync speed is wrong, you’ll end up with a picture like you see above, or even a completely black exposure, which is so frustrating. Read on and learn the most important concept to mastering flash photography.
How to Beat the Black Bar of Death
Basically, you just need to choose a shutter speed that doesn’t exceed your camera’s flash sync speed, and you’ll be fine. What is your flash sync speed? You’ll have to consult your manual to be sure, but it’s probably about 1/200 of a second (My Nikons were all 1/250th (1/500th for D40!), and my Lumix cameras are, too). When using a flash, set your shutter speed slower than or equal to this speed, and you’ll have no trouble from the “black bar of death”.
I think understanding why this happens is valuable, though, and may even allow you to make creative use of the sync speed somehow.
The Flash Synchronizes with the Shutter
Here’s how it works. Your camera’s shutter is like two curtains covering a window. When you trip the shutter, the first curtain opens to reveal the sensor to the light coming in through the lens, then the second curtain closes to cover it back up. The time that the curtains are open is the shutter speed. If you use a really fast shutter speed, like 1/4000 of a second, then the first curtain begins opening, and the second curtain begins closing almost immediately afterward, so there’s just a slit open between the two as they move across the sensor. When using available light (so-called Natural Light), it doesn’t matter what shutter speed you use because the light is always on and it comes through the lens even when there is only a slit to come through.
But when you use flash (or strobe), the flash is only on for an instant. If the curtain (shutter) is partly closed when the flash fires, then light is not shining on the part of the sensor that is covered and you get the black bar on part of the picture.
Your camera’s flash sync speed is the fastest shutter speed that exposes the whole sensor before the second curtain begins to close. The camera synchronizes with the flash so it lights up the whole sensor while the curtains are both open wide.
Of course, if you use a slower shutter speed, then the sensor will be exposed longer than the minimum necessary to sync with the flash, and you can do some fun things like I described in this other article.
Some flashes, like the speedlights made to work with your camera, are capable of High-Speed Sync. That allows them to pulse rapidly at high shutter speeds and send light through that little slit at every point across the sensor. There are two tradeoffs: these flashes are more expensive, and using these pulses of light reduces the overall brightness of the flash. You can shop for flashes capable of high-speed sync (HSS) that are compatible with your camera brand.
Using natural light is a wonderful way to work, but it’s not the only way to work. If you can learn to use strobes, you’ll not only be able to make a picture when it’s dark outside, you’ll also be able to create with the fun effects flash photography offers. The hardest thing about flash photography is just understanding the sync speeds, and even that’s not so tough. So go ahead and experiment with light–that’s what photography is all about.