Eli5: Why does a camera have to flash and time it perfectly when it takes a picture? Can’t the light just stay on?
In: 4956
So there are several considerations here:
* **Energy:** Studio “hot” (continuous) lights use a very large amount of power (500 w per light is fairly reasonable). Even still, a flash can generate more light within the narrow amount of time that a shutter is open.
* **Motion Freeze:** Flash allows better ability to “freeze” an image and reduce blur. The speed is faster even than a shutter speed of 1/250 of a second
* **Undesirable Light:** Flash is less likely to cause a model to squint or light your backdrops on fire
* **Portability/Efficiency:** Flash units can run on a small power source since they slowly charge up a capacitor. A disposable drug store camera runs a reasonably powerful flash on like a single AAA battery. This is much more efficient because all the light is released while the shutter is open so energy isn’t wasted
* **Power:** The actual power that a flash releases can be in the tens of thousands of watts!! This is because a fairly large amount of energy is discharged in a very small amount of time.
* **Overpowering Ambient Light:** Since flashes are extremely brief and synchronize to a shutter, you can use very fast shutter speeds. This will prevent ambient light from affecting the image. If you don’t want overhead lights, a window, the sun, etc. from affecting the image, you can use a very fast shutter and overpower the light with flash which is as bright as lighting (but for a very brief moment). If you *do* want ambient light to be part of the picture, you can adjust for this too and use both a flash *and* a longer shutter.
A few more misc things regarding flash in common use:
* **LED Flash:** “Flash” on many mobile phones is not really a true flash and just an LED light. Im not sure why it pretends to be a flash and only fires in bursts (on my Moto droid phone). Maybe its trying to prevent the subjects from squinting?
* **Combined:** Studio lights often combine a “hot” continuous light with a flash in the same light head. The continuous light is dimmer but lets you “preview” what the light looks like and helps you set it up/pose your model/subject.
TLDR: Photographic flash is very much like a lightning strike. A lot of energy is stored up slowly and then released very quickly.
Latest Answers