Not very important but interesting

[peterl]

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.

[Ray-uk]

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.

[ebiggs1]

"There is a sensor,..."

Actually a micro switch.  You can see it if you look closely.  Ditch the cover you don't need it.

[TCampbell]

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.)

[peterl]

Thank you, I can see the leafspring now.