Laser-powered DSLR Auto Focus Assist Light


[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.

28 thoughts on “Laser-powered DSLR Auto Focus Assist Light

  1. I think IR light will also do the trick, but i haven’t tried it.
    If it does, you just have to swap the laser for an IR one or some IR LEDs that can be left on all the time as they will not be seen in the picture.
    Maybe i’ll give this a try some time.

  2. Canon needs to give this person a job. An integrated laser is a much better solution than carrying around a big ass flashlight (like I do).

    @Bogdan, the CMOS censors in the Canon cameras (and CCD in others) are sensitive to near infrared. It would likely show up in images. Also the auto focus works on visible light otherwise the focus would be off since infrared travels through the glass in the lens differently than visible light.

  3. any decent camera flash will increase the AF light and you really do need to project a pattern as AF uses vertical edges to focus on.

    My low grade “promaster” flash has a huge AF assist lamp on front. make a huge difference than the useless built in one on the Canon DSLR’s.

  4. (Warning, I don’t know electronics well)

    You could use the signal on the hotshoe to turn OFF the laser for xxx milliseconds while the camera is taking the picture, then leave it on as long as it’s switched on. Sure, not completely automated, but better than the current situation.

  5. Interesting. Though I don’t see why one doesn’t just mark on the lens the distances associated with focus.

    This is basically substituting technique for convenience.

  6. @Renee They don’t do that because not all lenses are parfocal(the same position of the focus ring doesn’t correspond to the same focus distance for various focal distances) and because in some cases the DOF is so small that a few cm off will make the photo useless.

  7. Not knowing the subject of the photo I can’t really say much as to how much freedom can be take with DOF so I agree with you.

    However, it’s not entirely a grand mystery as to the nature of his lens. Making the safe assumption that it’s his camera in the pictures, he has a 50mm 1.14.

    It’s not that hard to learn the in and out of the focusing of a fixed focal length lens. Even including DOF.

  8. I have not tested it but if you search ettl pinout you can find a page with the pinout from the flash hotshoe. If I recall correctly the bottom left pin goes high when you hold the focus. I’m sure that logic can be used to turn on and off a LED.

  9. Watch your eyes though, because you can’t see it the danger of reflections is high.

    There is a good reason why they only used a 10mW diode in the Kinect.
    IIRC its a VCSEL, because they are single mode AND power limited due to the construction, so in worst case they just stop working rather than generating a dangerous situation.

    Same as “laser” mice which are just the thing for low power (1mA!) beam break detectors.
    Check out your local PC shop as they seem to regularly fail due to blunt force trauma and normally the diode lives on.

  10. Renee,

    do you have laser rangefinders for eyes? I know that shooting wide-open at f/1.8 I could never nail focus just with the index on the lens, for a variety of reasons.

  11. I like how things are overengineered. From manual triggering to hotshoe sensors, arduino to time… Why not just stick a photodiode on the original AF lamp that will trigger the custom AF lamp?

  12. I have a piece of tape that I use and I mark it with a pencil. If I know the general area my subject is going to be in, I mark the nearest and farthest point.

    Lenses use to have information like this printed right on them in the form of nice adjustable scales. I don’t know why they got rid of them. Probably because digital just makes everything super convenient.

    Not that I have a complete problem with that but it does cause some unnecessary reinventing of photography.

    How do you think people focused before autofocus was invented?

  13. Sony has had two cameras that do this – the V1 and V3 both I had the pleasure of owning, awesome p/s cameras for their time.

    They blast a hologram on the subject and can see it plain as day, and can calculate range via it.

  14. How do you think people focused before autofocus was invented?

    Cameras came standard with viewfinders that made it easier (split screen, microprism, etc) while now they just have ground glass. I can’t manually focus visually in low light, and I’m poor at judging distance so the distance markings are not a huge help to me.

    This is a brilliant idea. Too bad I don’t know enough about the electronics of the camera to offer any help.

  15. How do you think people focused before autofocus was invented?

    The same way I do with my MF lenses? Not well, in the dark. If you’re not looking at the ground glass, then a focus scale isn’t going to help at wide apertures, because a tiny movement of most focus rings is going to put your subject right out of the plane of focus.

  16. @Emm – the ST-E2 has a focus assist just like the ohter main Canon flashes – nothing special and it’s regular light. The IR is used, not for focus assist, but for communication ETTL info between the ST-E2 and other flashes.

    @Renee – At 50mm f1.4 there is no room for error – 1 cm off can ruin the photo – yes eyes out of focus and nose in focus . There is no way a average human could make the calculations necessary with out some electronic help.

    – Kyle

  17. @Renee I used to focus just fine in lower light situations before AF. I also had split screen to help me, and much younger eyes. Now, my problem is how to focus when using off camera flash, and shooting dancers that are continuously moving. Kinda hard to chase them around with a tape measure, or to see any markings that I might put on the lens, while chasing them around a dark room.

    I saw a guy the other night that was using off camera flash, but had a red focus assist light on top of his camera. Anyone have any idea what that was?

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