TTL and Manual Flash Modes
While using automatic mode on your flash and camera will yield good results for a majority of the time, there is the potential to get better results by having manual control over some settings. The mode we choose will determine if the brightness of the flash will be controlled by you or the camera. While manual mode has its uses, for beginner flash photographers this route often leads to more trouble than it’s worth.
Manual flash requires time to set up and a lot of fiddling with power settings without years of prior experience to draw from. Once the power is dialled in, this setting will only be good while the photographer remains the same distance from their subjects. If the subject moves closer or further away, then the flash power must be adjusted manually to compensate.
TTL is better option for beginners is to use. This mode will automatically adjust the power of the flash as the scene you are shooting changes. TTL is typically quite accurate on modern flash and camera systems, and any inconsistencies can be either corrected in post production or via the flash compensation system.