Flash Photography Tips
Part 2: TTL Flash Photography
In the previous article I discussed one important aspect of the differences between Flash Photography vs. constant light photography, which is the shutter speed. In this article I am going to talk about TTL vs. Manual Flash Photography.
What is TTL flash?
TTL stands for Through The Lens. With TTL flash, the camera and flash control the flash output (i.e., the power) as you adjust any of the other settings. That’s it in a nutshell – the differences between Manual flash and Auto / TTL flash.
How does TTL work?
Flash metering is achieved through the lens, using the camera’s metering system as it analyzes the scene through the lens you’re using.
Nikon first introduced TTL (Through The Lens) flash technology in 1980. The basics of TTL operation is rather simple and applies to all camera systems. With TTL flash exposure, when the shutter is tripped, the light from the flash fires off, racing to hit the subject. Let’s look a little more in depth at how TTL flash works. When you press the shutter release, a TTL flash will fire a Pre-Flash before the actual shot and the camera measures the Pre-Flash with the ambient light level to calculate the power needed in the actual flash for the shot. Don’t try looking for a Pre-Flash though, it happens very fast, only milli- or micro-seconds before the main flash, so you will only see one flash, not two, because the human eye is too slow to able to separate and see the two individual flashes. (The Pre-Flash in TTL flash photography can cause blinking in some people.)
Why is it important to learn how TTL Flash Photography works?
In manual flash photography you need to constantly adjust the out put of the flash according to the ISO, F stop, and distance. With TTL flash, the flash output is varied and controlled by the camera’s metering system. This means that within a certain range, our chosen aperture or ISO, or distance to our subject, does not influence our TTL flash exposure.
This is such a crucial point to understand about TTL flash, that I want to mention it again for emphasis.
With TTL flash, our chosen aperture or ISO (within a certain usable range), does not affect our exposure – and in a sense becomes transparent to our exposure metering. (Our camera and flash work together in calculating what it deems to be correct flash exposure, by increasing or decreasing the output from the flash.) What does affect our exposure, is the reflectivity of our subject, and how large our subject appears within our frame.
In other words: Aperture and ISO do not control flash exposure when we use TTL. This is because the camera will tell the flash to emit more (or to emit less) light as the camera deems necessary for correct exposure.
Then how can I control the exposure in TTL flash?
The only way to control TTL flash metering is with Flash Exposure Compensation. While you can control Manual flash exposure with any of the four variables mentioned earlier, with TTL flash you must use flash exposure compensation to influence or make changes.
What is the better metering mode for TTL flash?
The best metering mode is Centre Weighted mode when working with TTL flash, for better results than with the other modes.
What is the best Exposure mode in TTL flash photography?
You can shoot TTL in any exposure mode, but the one I prefer is Manual exposure. Since your camera controls the flash output, in manual mode you can set your shutter speed (within the synch speed), ISO, and aperture according to how much of the ambient light you want to capture, and your flash would fire the correct amount of light to lighten the subject. I cover more about TTL exposure in our TTL Flash Photography Workshop with plenty of opportunities to shoot and compensate for ambient light.
That is all for now. If you want to learn more about Manual shooting check out our new Manual shooting in Field Photography workshop on April 2. It is a full day of field photography where we are going to use only Manual exposure mode. Or check our Upcoming Classes to find more amazing photography workshops.
Ted and the Omnilargess TeamShare