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I'm new to photography and I see the term TTL all over the place. What does it mean? And how do I use it to make my pictures better?

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more info here : –  decasteljau Nov 5 '10 at 14:27

3 Answers 3

up vote 20 down vote accepted

It means "through the lens" and generally it hooks your flash into the exposure system of the camera since the metering of the scene is through the lens. This allows the camera to exert control over the flash, including power, distance, etc. based on the scene and focal length, if the flash supports that functionality with your camera. Usually true for modern flashes made by the camera manufacturer and some third party options such as Metz.

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As John says the term is usually used in reference to flash meeting. TTL meeting may improve your exposure it won't necessarily make your pictures any better! Basically the flash sends out a brief pre-flash and measures the amount of light reflected back off the subject through the lens. This is used to judge the required flash power based on your camera settings, the amount of ambient light, subject distance etc. It's helpful when you're moving around a lot and don't have time to be shooting test shots.

It can also be used with multiple off camera flash setups where you can choose the lighting ratios and have the camera work out the flash power for you. Joe McNally is a strong proponent of this way of working.

But for all it's advantages it's ultimately away of determining the correct flash power - TTL alone won't make your photos any better, learning how to use light, blending flash with ambient and most importantly bouncing flash where possible will go further toward making your photos better.

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Although current TTL systems are preflash based, older ones measured during the actual exposure, with a sensor reading reflected light from the film plane. –  mattdm May 28 '11 at 12:12
Who's Joe McNally? –  Sachin Kainth Aug 28 '13 at 14:42

While TTL is mostly used in context of flash metering, it could also refer to basic light metering through the lens (especially in context of older cameras, when this was a luxury feature). This is how most current cameras meter their exposure. You use it to let the camera set proper exposure for scene you have currently framed, and fine-tune it by setting exposure compensation.

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