There are some situations that you fail to focus in low light environment. And you do not want to use flash. With Canon Speedlite 580EX II, you can get focus lock on object in low light environment but it does flash too. How to enable AF-Assist Beam without flash on Canon Speedlite 580EX II with Canon EOS 400D Digital?
I searched online for quite some time and I got a solution. It is kind of a hack to the Canon Speedlite 580EX II. Anyway, it does the thick that I want. But it has limitation too. It cannot emit horizontal (periphery) AF-assist beam. Only vertical (center) AF-assist beam will be emitted.
How to disable flash and use AF-assist beam only on Canon Speedlite 580EX II with Canon EOS 400D Digital? Change the custom setting on Canon Speedlite 580EX II will do the trick. Change C.Fn-05 Flash metering mode from 0 (E-TTL II / E-TTL) to 1 (TTL). Canon Speedlite 580EX II will not able to perform properly with Canon EOS 400D Digital as TTL is used at film SLR camera. Therefore, it will emit AF-assist beam only without flash.