From my last post(AF Assist tool v3.0 – more testing)I discovered that the LEDs I have found are just not cutting the mustard. Today it just happens that I receive a red cross hair laser I ordered from Deal Extreme a few weeks back. I had all but forgotten about it.
So I stuck 3 volts onto it, and put it through the paces like I did the LEDs in the last post. The laser is bright. At 40ft (in pitch black), it’s very visible. Too bright in fact. So I stuck some resistors in series with the 3v battery to see if I can dim it. At 60Ω, the laser is dim. So dim in fact that in a brightly lit room it’s hard to see at a few feet away on a white wall. Yet when I turn the light off, and point at the wall 40ft away, the camera can still focus (with the center focus point) on the flat featureless wall. (I will post some pictures soon)
Not having had much success so far with LEDs and this laser module arriving in the mail I think I will rebuild my tool using this cross hair laser. Really I just need one line. The perpendicular line is of not much use. I really want this line laser from DealExtreme. I just ordered a few.
Ideally it would be nice to have several lines (close together) to allow for a little misalignment of the laser line and the focusing points be projected out of the same laser, but I haven’t yet found a diffraction lens that will do that.
Since contract is really what makes the difference in helping the AF sensor focus (as opposed to more light), the laser line is perfect since the light it produces remains sharp (distinct edges) up to a very long distance. And the line gives the enter focus point something to focus on regardless of the subject distance, whereas with projecting a spot, the will be some distances where the center focus point will not line up with spot of light.
As a start, I will add a potentiometer in series with the battery to adjust the brightness (a 100Ω pot should do it). Eventually I want to go with full PWM dimming control, so I don’t needlessly drain the battery.
Now if I can only find a laser of a higher wavelength, so that the light is nearer IR. The current laser is 650nm. Something in the 750nm range would be interesting to experiment with. If anyone knows of a source of inexpensive, low power (under 5mW) near IR laser modules (700nm – 800 nm), please let me know.
So you can get any pattern projected… Frankfurt Laser does a variety of patterns that may work very well. The Concentric circles I think would be awesome since it could cover most/all AF points very nicely