Definition: Through-The-Lens: adjective: ~ metering, ~ focusing: optical and electronic system in camera in which readings by the camera's sensors are made through the camera lens. * For exposure measurement, sensors may be placed in many different places around the light-path: looking at the focusing screen, sampling directly from the light-path or via reflections off the film or shutter curtain. * Modern auto-focus cameras commonly take exposure readings by sampling from the beam that supplies the auto-focus sensor or may even read from the auto-focus sensor itself.

Related Terms: OTF

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