[Adrian] uses his Canon 40D quite often in dark or low-light situations, and found the onboard auto focus assist functionality to be a bit frustrating. In certain focus modes, the auto focus assist light is programmed to turn off once focus has been achieved. He noticed that if his subject moves or the focus point changes before he snaps the picture, the AF light does not come back on to assist in refocusing the image.
To work around this problem, he decided to build a supplemental auto focus assist light that could be triggered at will. He purchased a cheap laser pointer with an adjustable lens, then cut it open to get at the good parts. He mounted it on top of his camera and tweaked the lens to produce an unfocused beam of light that measures about 6” x 12” at five feet.
The laser pointer did the trick – his images are coming out much nicer now that he can easily recompose his shots in low light. While it works great, he’s not completely satisfied with the build, especially with the fact that he has to manually trigger the laser pointer.
Version 2 is in the works however, which employs an old hot shoe to trigger the laser whenever he pushes the shutter release halfway down. According to his blog he is having some timing issues, causing him to capture the laser in most of the pictures he takes. [Adrian] is working hard to correct the problem, and we’re sure he’d appreciate any tips you might have.