02-12-2018 02:07 AM
I was in a camera store on Saturday and asked if they had hot-shoe covers for my 70D and they had so I bought one. On Sunday I tried to take a photo with the built-in flash just as fill in but the flash would not deploy, I tried every mode to get it to deploy, no joy, then, the hot-shoe cover dropped out and Lo and Behold the flash started deploying, there must be some sort of sensor in the hot-shoe.
02-12-2018 06:18 AM
There is a sensor, it detects when an external flash is fitted and prevents the internal flash from activating.
You used to be able to buy covers with a cutout on one side that wouldn't actuate the sensor, not sure if they are still available or even practical for more modern cameras.
02-12-2018 11:26 AM
The switch/button hides under the leaf spring on the hot-shoe rail. It keeps the flash from popping up and crashing into something if you have something in the hot shoe (such as an external flash, or an external video mic, etc.)