Urgent bounce flash question 760D owners

Goatruckus wrote:

I can't answer the OP question about the 760D because I have the same question.

I will say that the 70D problem is real. I have tested the 70D side-by-side with a T2i using the several different Canon lenses, and two different Canon flashes with the same mode and metering on each camera (tried several combinations). The 70D under-exposes in all bounce scenarios with all the equipment I tried, but you can't do a simple flash exposure compensation to fix it because it's too inconsistent. The only "fix" is to use Flash Exposure Lock (FEL) before each shot.

The 70D works the same as every advanced Canon camera released since the mid 2000s. Internet forums have chatter about this "bug" in the 5D2, 5D3, 60D, 70D, and 6D...

A post from 2008:
http://photography-on-the.net/forum/showthread.php?t=616395

"In fact, with Canon ETTL, over many years it has been a chronic complaint that the flashmetering underexposes, and many of us dial in FEC +1EV even for direct flash, not merely for bounce flash."

5D II:
http://www.fredmiranda.com/forum/topic/880510/0
http://photography-on-the.net/forum/showthread.php?t=639531

5D III:
http://www.dpreview.com/forums/thread/3222627
http://photography-on-the.net/forum/showthread.php?t=1333705

6D:
http://www.canonrumors.com/forum/index.php?topic=22936.0

60D:
http://photo.stackexchange.com/questions/50233/e-ttl-underexposure-with-flash-zoomed-in-and-shot-through-a-modifier

An interesting comment:
"When using modifiers it is generally a good idea to manually set the flash's zoom to a wide angle and leave it there regardless of the focal length your lens is zoomed. Here's why: The pre-flash used by E-TTL is a fairly low power pulse compared to the flash's full power. The camera doesn't need to be able to see perfect exposure during the pre-flash, it just needs to measure how much of the light emitted by the pre-flash is reflected back to the camera and then assumes the same percentage will be returned at higher power levels. With the modifier between the flash and the field of view the assumption that the same percentage of light emitted by the flash will be reflected to the camera's sensor may be an incorrect one."

All the advanced cameras, as opposed to the Rebels, attempt to balance the flash level with the ambient light level. The Rebels, apparently (I don't own one) assume the flash is at all times the primary light source.

This post details how ambient light levels affect the flash exposure balance in these cameras:

http://www.dpreview.com/forums/post/56112358