AF Assist tool – Version 1.0
Last september (2010) I wrote a blog entry about hooking up a laser pointer as an Auto Focus assist light for a camera. The need came up because I wanted AF assist in AI Servo focusing mode of my DSLR. Currently to my knowledge all Nikon and Canon DSLRs will only put out the flash AF assist beam until focus is achieved. After that if the (if the camera is in AI-Servo focus mode) if the subject moves and the focus changes, you’re out of luck in dark situations because the AF assist beam will not continually come on to keep assisting the focus.
The previous look at using a laser pointer as an AF assist tool, I had very little success with that projects. Last week I came across the laser pointer again and new thoughts/ideas came to mind.
So I rigged a laser pointer to a bunch of batteries and a push button to act as an Auto Focus assist to my Canon 40D. The results are spectacular.
I’ve already started working/thinking about the next version of this. Updates on the AS Assist Tool V2.x will be here.
This is what I did, and how it worked.
The idea for how to put together this setup came when I saw the spare hotshoe and the laser pointer together. The hotshow is from an old Minolta flash. I long ago threw the flash away, but kept the hotshoe in case I had a use for it.
The dollar store laser pointer got dissected (the aluminum casing got hack sawed length-wise) and the board with the laser LED and focusing lens (the two are attached) came out easily.
The laser pointer got hot-glued to the hotshoe, (after being adjusted so that it lined up with the camera’s AF points) and it was ready for use.
One thing I should mention is that the laser pointer’s focusing lens is adjustable. It can be rotated (the lens mount has a cutout where a flat screw driver can be placed and rotated) to adjust the focus of the beam.
At 5 ft the beam is about a 12 inches tall and 6 in wide. (the ruler is 12 long). The center focusing point was lined up with the center of the ruler, on the bottom edge. The light coming out of the pointer is not an even light. There’s a random pattern to it likely from the imperfections of the focusing lens, but it’s a good pattern as it assists the AF sensor focus even on a flat white wall (onto which an AF sensor would not be able to focus).
I have not done any scientific analysis to determine an optimal size of the unfocused beam. It just seemed like a good size, and it worked well.
There are two main reasons to use an unfocused beam from a laser pointer if you plan to use this kind of a setup. First is that a focus point of light will only line up with an AF sensor point at a certain distance from the subject. At any other distance to the subject the laser point will not line up with the AF sensor point.
Second if you’re photographing people, (which is what I do) I have some reservations about pointing a focused laser beam at someone’s face/eyes to assist the focus of my camera. Defocusing the beam produces a much weaker beam of light. Combine that with using 1.2volts NiMh rechargeable batteries instead of the 1.5V button batteries the laser pointer uses and you can further create a weaker/less dangerous light pattern.
I have used this setup at a dance club the other night with great success. I had sharp focus on way more images then ever before.
To power the laser pointer LED I used a 3 AAA NiMh batteries totaling 3.6V. The original laser pointer used 3 1.5V button (watch) batteries so a total of 4.5V so if I need more power I can still go to 1.5V cells to more light if I need it.
I have asked several people which I photographed if the red light bothered them, and they all told me that they didn’t even notice it. The fact that I was in a night club with lasers and other lights flashing may have swayed their attention away from my puny unfocused undervolted laser beam.
The batteries and laser LED were hooked up to a momentary push button so control of the AF assist light was done entirely by hand. This is not the best setup for a few reasons, but it works and would do it again if I had to. For one, the small push button gets hard to hold after holding it for a couple of hours. As the hands sweat a little, it becomes sliperry… Also the hand that holds the push button doesn’t have a secure grip of the camera.
I did however like the control the push button provided. In the next version of this tool I will see if I can automate the process of turning on the AF beam by the use of the electrical connection between the hotshoe and the camera.
These are a collection of images of the tool.
On an aluminum plate was mounted the battery pack. The hotshoe to the left of the battery pack is simply a spot to attach the wireless flash trigger (which gets connected to the camera by use of a sync cord). One set of wires goes to the white push button , and the other wire goes to the hotshoe with the laser pointed mounted on it.
Below are some more photos of the setup.
The next step is to clean up the entire setup, stick it inside a project box so that everything can sit on the camera’s hotshoe neatly. Also try to control the AF assist from within the camera to eliminate the need for the push button.
Usability issued aside, I was very very pleased with the results I got from using this laser pointer AF assist. The ability to maintain focus as subjects are moving in a very dark (night club) environment was priceless for me. The AI-Servo mode on my 40D didn’t skip a beat while the laser pointer was on. I had more trouble keeping the subject on the camera’s focus point. The photos I captured with this new tool are on my blog/gallery here.
I’ve already built V2.0 based on this schematic. Build v2.0 is not documented very well.
Build v3.0 is in the works, and will be documented.