TTL mechanisms in cameras are not new – the first daguerreotype and wet-plate cameras all were fitted with TTL capability. The light went right Through The Lens and made the picture. Of course the photographer had to do a few things along the way and the speed at which the picture went TTL and out the other side was pretty slow…
Joking aside, TTL light metering started to be big in the 1960’s and now TTL control for flash photography is all the go in the digital world. Sigma, Nikon, Canon, Fujifilm, Olympus, and the lurching corporate zombie that once was Metz all make speed light flash guns that do TTL flash monitoring ether on or off the camera. And they do it very well.
The mechanism acts by emitting a tiny test flash, analysing the impact that this has on the scene when it bounces back through the lens, and then regulating a second, main flash to give what the designers think might be a balanced exposure. Bless them, they are right much of the time.
Love it as a technical achievement for weddings and parties. Hate it as an anchor around the neck at dance shows.
It slows down the exposure sequence just enough to take you from the peak of the action. Combined with auto focus delay it can make every shot wrong. Plus if you give it a funny situation, it will give you a funny result, and you won’t be laughing.
The answer is simple; I turn it off. The flash is run in manual, the focussing is manual, and as the shutter speed and aperture are fixed, the exposure returned is the same for each shot. Do about 5 test shots before the performers are on the stage ( and do them with a McBeth chart if you can ) and you’ll be able to nail at least 50% more of the action and have 50% less processing variation later on the computer.
The heading shot is at 1/125 second and f:8. So is this one, and the difference in the reflectivity of the costumes would have had the TTL flash mechanism and exposure measurement all over the shop. As it was, they both came into LR6 at the same intensity and just needed cropping.
Yay for the old way of doing it.