Using sigma ef-500 to focus in low light situations?

Is it possible to use the sigma ef500 dg super to perform auto-focusing (override the camera's focus)? I checked the manual but couldn't find this feature. I think it is possible by using a canon 550.

Take a look at this thread:
https://photography-on-the.net …php?p=1270897#p​ost1270897

Using custom functions to turn on the AF assist beam, but turn off the flash, should do the trick.

The flash unit doesn't perform autofocusing, or override anything in the camera. The flash unit's infrared focus assist beam simply projects lines of light on your subject, to give the camera's AF system the contrast that it needs to work.

Thanks Curits. I did a search before posting but couldn't find that thread.