TTL flash in photography
Measuring the intensity of a flash so that it optimally illuminates its object isn’t a hard task. By using the GN formula (at ISO 100) = distance x aperture, we’ll be able to calculate the distance or aperture that’s optimal for certain conditions when photographing. But of course that formula won’t be valid when we’re using a that can alter the amount of light that enters the lens, such as a CLP or GND filter that will lessen the amount of light that enters the camera lens. To accommodate it, camera specialists have created a flash technology that can automatically measure the light intensity that enters the lens. This automatic measuring technology is called the through-the-lens (TTL) Metering.
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