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Harsh, unflattering lighting can ruin a photo—and with flash, it's easy to get harsh, unflattering lighting. But flash is a necessary part of a photographer's toolset—after all, the world doesn't always provide you with the best natural light.
Fortunately, it isn't difficult to get great results from flash, and in this course, photographer, author, and teacher Ben Long details the concepts and techniques behind effective lighting with flash. Ben starts with fundamentals that build on exposure principles taught in other installments of Foundations of Photography—simple techniques that improve the results from a camera's built-in flash. He then focuses on fill flash techniques and on using flash as a key light. The course also explores topics ranging from bouncing and syncing flash to shooting with one or more off-camera flash units.
When you shoot without a flash, you are probably used to setting shutter speed to whatever is appropriate to get the motion stopping or blurring effects that you want in your image. Sure you have to balance that decision against depth of field concerns and the noise response of your image sensor but even with all those considerations you still have a huge amount of shutter speed latitude to play with from full minutes to tiny fractions of a second. When you start using a flash that all changes. When you shoot with a flash, there's a limit to how fast your shutter speed can go because of the way that the shutter in your camera works.
Most cameras that have interchangeable lenses have a type of shutter called a focal plane shutter. This is a shutter that sits, not surprisingly, near the focal plane. Directly in front of the image sensor, or film. This is, as opposed to shutter mechanisms that might be housed within the camera's lens. A focal plane shutter is composed of two curtains. Sometimes made of cloth, sometimes made of metal or plastic. To expose the sensor, one curtain opens, and then another curtain follows to stop the exposure.
In a really fast exposure though, this means that the entire sensor will never be completely exposed. Instead, a slit of exposure will pass across the surface of the sensor. Now if you fire the flash when only a slit, a small part of the sensor is exposed, then only that part of the image will show the flash illumination. So after a point, shutter speed gets too fast for the flash to be in sync with the full exposure of the sensor. When shutter speed is too fast and the flash is out of sync you'll get strange dark bands in your image.
All cameras therefore have a flash sync speed. Any flash picture shot with a shutter speed faster than the flash sink speed will result in an image with this dark banning problem. With shutter speeds below the flash sync speed there will always be some moment, during the exposure, when the entire sensor is exposed, that's the moment when the flash will fire. Because that's when it can illuminate the entire image. Your camera manual will list the flash sync speed of your camera. On most SLR's it's around one, two hundredth of a second, in other words you won't be able to use a shutter speed that's faster than one two hundredth of a second, and still get good flash results.
Because at faster speeds, the shutter will never be entirely open. Some cameras might go as low as one sixtieth and some might go up to one two fiftieth. Now as you'll see later, there are high speed shutter techniques you can use to get around this limitation, and we'll cover those in detail. A few cameras that have interchangable lenses employ what's called a leaf shutter. This is a shutter that can open almost instantenously. A leaf shutter has the advantage that it has an incredibly high flash sync speed. At the time of this shooting though there just aren't a lot of leaf camera shutters on the market.
So, no matter what mode you're shooting in, you will always have an upper limit on the shutter speed that you can use reliably. Note, that your camera will let you use a shutter speed that's higher than the flash sync speed, you just won't get a great result if you do.
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