Modern DSLRs are equipped with light sensors to measure ambient light. The lens of the camera also affects this measurement.
TTL flash metering (Through The Lens) is a great way to adjust your exposure. TTL flash metering does not base your exposure on ambient light. It instead bases it on what flash output light you will have (based on a few variables).
Two basic methods can be used to measure flash. The first is to measure the flash’s light burst while it’s being projected. The second method uses a preflash to measure the light snapped as it’s being launched. This is used for exposure calculations.
TTL and ATL use the first flash metering modes, while automatic TTL and evaluative–TTL use the second. A flash unit that can E-TTL is capable of high flash sync. Let’s now discuss these three modes in more in-depth.
TTL Flash Metering refers to your camera’s standard metering mode when you use the built-in flash or pop-up flash.
This metering mode can be used with specific flash units available for your camera. TTL flash metering measures flash output light reflected from the subject and then takes the reading through the lens. This will measure the area in your view with the active focusing point. TTL controls flash exposure using a dedicated sensor, which measures flash output reflected from the surface of the image sensor during dynamic exposure.
TTL doesn’t use a preflash for flash exposure calculation. TTL will select an aperture setting depending on how much ambient light is available when your camera is set up in Program.
The automatic TTL performs the same functions as the TTL metering modes in that it reads through your lens and focuses its sensitivity on the area covered by the active focus point.
A-TTL differs from TTL because it uses a preflash to preflash the correct f-stop based on the distance the flash output light must travel to reach the subject. The flash unit sends the actual scene-illuminating flash output when the shutter is fully open.
You can also set the camera to Program mode, use A-TTL, and compare the distance-based aperture and ambient light-based information. The camera then chooses the larger aperture (to increase sharpness and depth) and ensure a more precise exposure.
Evaluative TTL is a slightly different technology from TTL or A-TTL. It uses the preflash to preflash the best flash exposure. This is done by measuring the scene’s reflective qualities to create a mid-toned subject.
E-TTL’s preflash is preflash from A-TTL because it occurs immediately before the shutter opens (and not when the shutter is half-pressed with A-TTL). The exposure value is calculated before the central flash fires and not during the metering.
The camera’s primary TTL sensor analyzes the preflash external flash sensor. This allows E-TTL greater accuracy. Because of the preflash firepreflasht, it can be challenging to see it even if you try.
Photographers have found the TTL Metering system a boon, although it is less useful in digital photography. It lets you see exactly what your image looks like right after taking the photo.
Make any necessary adjustments to the image and then retake it. TTL Metering lets you be as exact as possible in your photography and has precise control over the exposure settings.
Understanding the TTL metering modes will allow you to be more creative in your photography. You’ll also better grasp the most crucial element of photography, how you capture the light.