So if i understand this correctly, Most nikon DSLR's have an actual assist light or halogen light that shine against a subject to focus in low lightand Most Canons use the "flash" to focus and then flash again to take a picture in low light, assuming your gonna use flash. Is one system better then the other? Deciding between a Nikon D7100 and a Canon 70DBoth cameras are pretty nearly equal from I've read.This is a "major" deciding factor about auto focus, but is one better then the other form your experiences or knowledge? Like faster then the other, or would a pre flash force subjects to blink etc?
The Canon pre-flash autofocus assist has a serious disadvantage. It never ceases to amaze me how quickly people react! Take a group shot with the flash; the autofocus flash fires; everyone decides you have taken the photo and looks away just as the exposure is made. That said... The onboard flash on any DSLR is utter garbage so why would you use it anyway! If you use a Canon speedlite then they have an autofocus assist system that projects a red hatch pattern and works extremely well. My 20 yr old EOS film camera has one of these red beams built into the body. If only Canon had carried it over to their DSLRs!!
I don't see one system better than the other. Why? In low light shooting, use manual focus. If you can't do it manually in the dark, it's not a good shot anyway. If you really have to, use a flashlight to shine your subject then focus manually.
