AF assist beam with external flash and 80D

[Tubeydude]

Hi all, I'm new here, but have had my 80D for about 5 years and really enjoy it.  I was trying to do some low light pics and used my external flash rotated to the side to get some softer fill light.  It was having trouble focusing in low light (not too surprising)  I usually just switch to manual focus when I have this issue, but as the subject was moving a bit, I though I would try turning on the AF assist bean that my flash has and see if that would help me out.  ( flash is a Godox TT685, which has also been great.)

I found that the AF assist beam on the external flash only fires when I am using the regular viewfinder, and when doing so, it greatly speeds up autofocus, as one would expect. However, If I go to live view shooting, the AF assist beam does not fire and the camera hunts for focus.

Is there a reason why the AF assist beam on the external flash would not fire when in live view shooting?  It seems to do this regardless of the shooting mode I'm in, P, Av, Tv etc...

I have the camera AF setting to live view plus tracking.  AF assist beam is enabled and red eye reduction is disabled? 

Thanks!

[kvbarkley]

Because the sensor is not sensitive to IR light because of the IR filter. It requires the phase detect chip that is active when using the viewfinder.

[Tubeydude]

Thanks!  That would explain it.  I guess the IR filter must be directly over the imaging sensor...

I wish there was a way to make the AF work better in lower light.  It looks like there is plenty of contrast on the live view screen, but it still hunts for focus, going right through it often.  I tried messing with some of the custom function settings, but didn't really see much improvement.

[kvbarkley]

Newer cameras, like the R series, have phase detect areas on the sensor. I don't think the 80D has that.

[deebatman316]

The Canon 320EX speedlite uses an LED light for an AF Assist Beam during live view shooting. When using the viewfinder the speedlite will pulse rapidly (intermittent flash firing method) to provide an AF Assist Beam during viewfinder shooting.