One of the most common questions I get is about shooting events for the first time with a flash. This is not a simple answer as every camera system treats flash a little differently. The safe, shoot answer is P Mode with ETTL if you are unsure. Many camera systems (not all) will detect a flash in AV mode and turn it into a slow sync mode, which drags the shutter speed, even up to 1 second of longer in some cases. You do not want this in event photography. Some Canon cameras will let us set the shutter speed limits and in those cases, you would be ok. There are some other options such as shooting in manual with a locked in SS, and using ETTL.
I hope this clarifies your questions! Best wishes!
Michael’s Camera Straps:
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