Key Points
- Your camera meters/measures both constant ambient light and flash lighting. It calculates and controls flash power settings automatically when flash TTL is employed.
- TTL uses a pre-flash just before actual exposure. This is a short burst of light on the scene that helps the camera determine flash power for the actual exposure.
- Your flash can operate in TTL mode in various camera modes, including Manual mode. This gives you the best of both worlds; you manage ISO, aperture and shutter speed (for total creative control), while the flash power is handled for you on the fly!
TTL Makes Flash “Automatic”
Through-the-lens (TTL) flash metering systems, such as Canon’s E-TTL II and Nikon’s i-TTL, liberate you from the tedious task of manually adjusting your flash output every time the distance between the flash and your subject shifts. Keep in mind, even a minor change in this distance can significantly impact the exposure. With TTL activated, your camera and flash collaborate to auto-adjust the flash output as the scene’s conditions fluctuate. TTL is versatile; it’s compatible with various lighting modifiers and allows the flash head to be in any orientation, perfect for bounce flash techniques. When you press the shutter button, the camera’s TTL flash metering system deploys a preflash—a quick, barely noticeable test flash—to gauge the optimal flash output right before the actual exposure occurs.
It’s worth noting that TTL is compatible with all standard camera modes, Manual mode included. This means the flash output will auto-adjust in tandem with changes you make to camera settings like aperture, shutter speed, and ISO. And while TTL does the heavy lifting in determining flash output, you still have the freedom to fine-tune the flash’s power using Flash Exposure Compensation (FEC).
Flash Exposure Compensation
Given the way TTL manages flash output, the Flash Exposure Compensation (FEC) setting on your camera becomes an important tool for fine-tuning your shots. In essence, FEC allows you to override the flash output that TTL automatically calculates. Whether you think your picture could benefit from more flash or less, FEC gives you that control. It’s a valuable asset for both indoor and outdoor portraiture. For specific guidance on how to adjust FEC with your particular setup, consult your camera and flash manuals.