06-26-2015 01:17 PM
06-26-2015 08:54 PM
Which flash are you using?
There was, for example, an issue with some 580EX II speedlights in which the screws that hold the foot plate in could become loose. If that happens then the pins may fail to get a good connection.
The solution was as easy as re-snugging the screws... complicated by the fact that the screws are actually tightened from the inside of the flash. Canon will do it for you if you send it back to them (assuming this is a Canon flash.) They had a service kit which replaced the footplate and screws with a newer design that should be less prone to becomming loose.
But this could happen to any flash. If the flash is on the camera and the locking lever in secured, the flash should have very little play (if you gently wobble the flash it shouldn't move much at all.) If it does wobble, then it's loose and needs service.
There are YouTube videos that show the issue and also show how to fix it (for the mechanically minded person.)
06-27-2015 09:30 AM
"The Camera developed a fault about a month ago. Would not communicate with the flash( photos over exposed ) and two vertical lines on the pictures."
Try a different flash. It does not sound like the camera.
06-29-2015 01:06 PM
Flash works perfectly on my 650d. It's not the flash
It's not really safe to draw that conclusion.
Specifically which brand & model flash is this? Third party flashes reverse-engineer the interface and it's happened before that one will work on one camera model, but not a different model.
The 5D III allows flash control via in-camera menus (previosu models didn't offer that to the degree that you can do on a 5D III). It's possible do dial in flash exposure compensation via the camera (instead of using the menu on the flash.) Have you checked that? And of course it's also possible to dial-in flash exposure compensation using the flash menu as well. Have you checked that too?
06-29-2015 06:18 PM
"The vertical lines appear on exposures flash or no flash!"
Doesn't this indicate it is not the flash as the problem?
If the "clowns" at Canon Service did not find anything wrong, I would start looking elsewhere.