Action freezing examples include a dancer jumping and long hair blowing with a fan as we examine flash duration and how much you need to overpower the ambient light to freeze action in the studio or on location.
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Rough Transcript
Well as you saw at the beginning of this video, I've been conducting flash duration tests this week for todays video.
But before we get into the results, we have to set the table.
Flash tubes emit pulses of light each time you take a photo, often with the burst being more intense in the beginning and then trailing off over time. The length of time that light is emitting from the flash is known as the flash duration. You can imagine this if you recall the effect of being blasted in the face with an on-camera strobe while posing for a photo. Flash duration can be expressed in two ways - t.1 and t.5. t.5 is when the intensity of the pulse reduces to 50% of its maximum intensity and t.1 is when the pulse drops to 10% of the maximum. The graph from Sekonic, demonstrates the relationship. T.1 numbers are far more useful to me than t.5 numbers, because they more fully represent the information but there isn't a formula to convert t.5 specs to t.1.
Flash duration specs for your light will most likely be in your manual.
Sync speed
The fastest your camera can send a signal to a flash normally and have it fire while the shutter is open is known as the sync speed.
In the studio, your camera’s sync speed isn’t much of an issue unless you have a lot of ambient light in the room. Typically if you’re adding so much flash to your scene that an exposure without that flash at the same settings would result in a black image, the only thing freezing motion in your frame is the flash duration. So effectively the flash duration becomes the shutter speed.
However, if you are using flash at 1/200 of a second, a common sync speed, with moving subjects outdoors during the day or in a bright room, you can get blurry images regardless of your flash duration because the ambient light will have an effect on your exposure, so you will want to either overpower the ambient light or you will want to use a shutter speed that can freeze motion on its own, but the only way to do that is high-speed sync and that is a whole other video.
I first learned of flash duration in the late 90’s when I was just a spry 18 year old photographer and I wanted to light an NBA arena. The older photographers I knew said you need a duration of 1/2000 or faster and you need to overpower the ambient by two stops in order to freeze basketball. I never ended up lighting an NBA game, but I did use this knowledge for college basketball, pretend basketball and minor league hockey. I just assumed what they said to be true and over the years I have questioned wether or not their advice was accurate.
So in a few moments we're going to investigate how fast your duration needs to be to freeze a dancer jumping through the air and how much you need to over power the ambient while photographing a model with long hair blowing in the artificial wind. Knowing your flash duration can also be important for applications other than extreme movement. I have seen motion blur in my frames when I was photographing models just posing in the studio and my flash duration was longer than t.5 1/1000 of a second.
Reducing the power output of your lights, unusually results in faster flash duration, but some models, like the Profoto D1, have their fastest flash duration at full power, so consult your manual to learn what power settings will result in the fastest duration and slowest duration for your light. But for most units, the fastest duration for your light will be at minimum power. So the brighter you make the flash the slower the duration will become.
Music: Evolution by Bensound bensound.com/
31 окт 2021
