Can an IR laser be used for focusing a DSLR in the dark?
How many watts is needed for 100m distance?
No direct answer, but:
Old Sony digital cameras had built-in laser autofocus assists, but that was a visible red and not IR. Wikipedia says other old cameras used regular IR light, not lasers, to focus.
A camera not designed to work with a laser probably can’t focus very well with it, because there’d only be one tiny dot for the camera to focus on (unless you had a special projector that did a grid setup like the Sony one).
An infrared flashlight, however, would likely work… and apparently a lot of cameras integrate them as “autofocus assist lights”, though the ones I’ve seen at least partially crossed over into the visible range.
It’s likely not the wattage you care about, but the lux, and how much you need depends on your camera, lens, and ambient light (as in any photo). More light generally makes focusing easier. Some cameras have the minimum lux needed for autofocusing in their specifications, so you might look into that. Also, do a test with the IR emitter with the actual camera you want to use it with… some cameras block out parts of the IR spectrum for picture quality and privacy reasons, so a flashlight below a certain wavelength might be invisible to the camera.
Today I got it working with Canon T2i! All you have to do is align them so the red focus dot is on top of the beam. It works out to 100m in the dark with my 300mm lens! What other cameras work like this?
I’m not sure that Sony feature was actually a laser. Many AF flash units for DSLRs do the same thing, and I think it’s a LED. The range is short, a few metres at best.
There were a few cameras that used an ultrasonic sound waves for autofocus. These, and the old IR autofocus cameras, were rangefinders, unlike modern cameras that focus by analysing the image.
Laser rangefinders exist that can measure a distance of 100m or more. I don’t know if they’re accurate enough for focusing a telephoto in a low light situation. Movie cameras are (were?) usually focused with a tape measure, it wouldn’t surprise me if laser rangefinders were used for long distances.
Color me surprised. Did you use a laser or flashlight?
I had one of those cameras and it sure seemed like a laser rather than a LED (the way the pattern glittered and shifted, and its sharpness, both seemed laserlike). That page I linked to above also has a laser sticker, and I presume Sony wouldn’t go through the trouble of getting certified (or faking one)… though I’ve never see a laser sticker like that instead of the usual class warning sticker.
Why do you need autofocus for a distance of 300 m? Isn’t the focus easy to set for such a large distance, or for all but the biggest lenses easy to set at infinity?
2W IR laser on Ebay for $3. It works at 100m. Did I type 300 by mistake? In the dark it is impossible to focus even on infinity. This is a new feature I like for star photography. A 300mm lens doesn’t require much focusing past 100m. But at 50m it is still critical in the dark. BTW I use a big flash which works at 100m. Without the laser I can only focus 4m away without a bright flashlight which scares wildlife. The built in flash doesn’t work past that distance, and it also scares wildlife. The IR laser does not unless they’re looking at me. When you open the aperture all the way to get the maximum flash distance focusing is especially critical. It works great for wildlife at night. It is important at short distances even with a mid-aperture setting. Sometimes we want a shallow DOF even with a flash.
You can focus it to a sharp beam which spreads out to an inch or so at 50m. At close range this could blind the subject. It’s safe to unfocus it for this range. Do not try this at home without experience and knowledge! Ask and I can help.
I stand corrected and am now fascinated. I hope to try this someday 
With a 300mm lens at f/4 on an APS-C camera like the T2i, depth of field at 100m is about 17m total (92-109m). Focused at the hyperfocal distance your depth of field would be about 600m to infinity.
I have to say I’m surprised as well, are you using an 808nm laser? I thought modern DSLRs had IR-cut filters that cut off around 700nm.
If you were an evil government and wanted a weapon to blind people for your Army how would you design a video system to track the eyes of the target? It would only take a millisecond to blind someone with 2W at 10m distance. Very portable for the laser bit only 3 oz including battery and heatsink.
Do you think I could sell a complete system for Auto Focus in the dark on Ebay? Sshh there’s really not much to it, but you won’t tell right?
The packaging and plastic case would look pretty.
@tellyworth- that is correct at 20m it is much more critical. There is just no other way to do it in the dark. The manual says my internal flash should focus out to about 10m? Does yours go that far? How about the expensive Canon flash?
I was surprised too! 808nm. Works instantly as fast as broad daylight.
Is there an alternative to focusing on infinitely on a moonless night in the desert?
Please tell me!
@scr- You are correct you cannot see the light thru the viewfinder or when you take a video or picture. But it works with AF!!!
It also works with Trap focus in the dark.
Unattended.
Wait until you see what I’ve designed with a cheap webcam…
There is no cut filter on it.
It can be used to trigger video in night vision mode.
What else can you do with an IR laser and photography?
I’d forgotten that the IR-cut filter is on the CCD itself, and the AF sensor is separate (duh). I guess the AF sensor doesn’t have an IR cut filter. Interesting…
Anyone try it yet?