Hi. When using my speedlights on my Canons (5D2 & 7D) in low light events I have no problem with autofocus. However, using my Quantum Trio ( which normally provides better color & more power) in similar in low light is virtually useless - my canons will not focus at all. This is very disturbing. Does anyone have this problem? If so, how have you resolved this ? I use center point focusing , f/2.8 or f/4L series canon lenses and partial (or matrix sometimes) metering. It appears that the quantum sensor is much smaller than the Canon speedlights- I wonder if that is the problem. Thanks. -Ben
Yes, thanks for reply. I've always made sure my autofocus is on, but your other suggestion about cleaning the focus lamp - I never considered that before! Anyway, I used a microfibre cloth and then tested my flash on both my cameras. The results were good, although there was still a very slight struggle with my 5D2 focusing. Now, my tests were in a controlled situation (my dark laundry room). My real test won't come into play until my next big event shoot in a few days.
Thanks again. I'm still open to other suggestions from others - I've researched this problem to death!
The Nikon version focus assist is really bright and the only problem I've ever encountered was the focus assist not coming on was either as previously pointed out -- it wasn't switched on -- or -- I had continuous servo focus set on the camera. In continuous servo the focus assist doesn't illuminate. I don't know whether this might be the case with Canon?
The Canon AF assist light projects a grid pattern. To be effective the grid pattern needs to overlap the AF points which work via contrast detection. That's what the grid pattern is for, to create a contrasting pattern. So it's not just the light level of the AF illumination, it's the pattern and how it corresponds to the AF points. The AF sensor is behind the reflex mirror on the bottom of the mirror box and the actual AF points don't always exactly line up with the indicators on the viewfinder.
Also as with AF in bright light it works better when the AF point is on an contrasting edge detail on the subject. AF sucks in any light if you aim the camera at a blank wall.
