Updated version available here. Version 3.1 is complete.

It’s done!

Version 3.0 of my AF assist tool is complete.

Taking a step back, I should explain why I needed this tool.There are really 2 reasons I built this:

1. When photographing concerts or clubs, or any other venue where light is at a premium, the AF sensor in the camera can only do so much to give accurate focus. I am using off-camera flashes most of the time now so I am not relying on the ambient light to paint my scene; that’s what the flashes are for, but I still need to focus. No remote flash trigger to date has had a AF assist light built into it. I use a Pocket Wizard Mini TT1 trigger and Flex TT5 receivers to trigger my flashes, along with an AC3 zone controller (which allows power control of 3 flash groups). So with a flash trigger in the camera’s hotshoe I loose my AF assist light, which normally I would get from a regular flash.

2. DSLR cameras (that I’ve looked at) don’t do AF assist in AI-Servo mode. They don’t allow you to track a subject in the dark, by continuously adding the light from the AF assist lamp on flashes to help the AF sensor in the camera continuously maintain focus. You get One-Shot focus, and once focus has been acquired, the light goes of. But if I want to track a singer as the move on a stage, like one would track a moving person or a race car during the day, you’re stuck. You can’t. This AF assist solves that problem but allowing full control of the AF assist light to be projected as long as you’re focusing (focusing is done by 1/2 pressing the shutter). Continue reading →

I decided to take apart the AF module from the 550EX flash mainly to see if I could use my own LED in the AF module lens.

The unit is comprised of a lens and holder assembly, and an LED assembly. The LED assembly has the LED (which I believe to be a near IR LED) glued to the back of a lens.

The pattern the AF assist module projects is created right on the LED itself, unlike the 540EZ module. The pattern created by the 540EZ module is drawn on a small piece of plastic that lives inside the module. On the 5503EX module, the pattern is right on the LED.

So it looks like there’s no replacing the LED in this module.

Using the same laser pointer as in my previous post AF Assist tool v3.0 – laser pointer trials, I decided to stick a cap from a dollar store laser. You know the caps. The ones that draw hearts, or arrow, etc.

I tried a few, and one really stood out as sharp pattern, and coverage across the largest area of the frame.

Frame coverage at 50mm, on a crop body (x1.6). Not a very large coverage, but the contrast it produces is very defined. Even at 40ft the image is crisp. All focus points have no problem locking on even on f2.8 lens (not just the center cross type AF point)

I will have to investigate other laser pointer caps to see if I can find something that has a larger area coverage and provide lots of contrasty details for the AF sensors on the entire frame to use to acquire focus.

There is this diffraction lens I can get  but I don’t think it will project much larger then the bow and arrow I already tried.

Ideally something like this
Frankfurt Laser Company – Grid
or this
Frankfurt Laser Company – Ring/Concentric
would be perfect, but again, it all depends on the size of the image it projects.

On the other hand the pattern can’t be TOO large because at distance it looses it’s contract effectiveness as the pattern gets to spread out.

This pattern will get too thinly spread out. It’s great if you’re only a few feet from the subject but much more then that and the space between dots/patterns gets too large and the AF sensors/points can too easily fall between the patterns.

Did some more experimenting.

The problem I am battling with (one of them at least) is that using the AF module out of the Canon 550EX flash uses way too much current to be used almost continuously. In my last post (AF Assist tool v3.0 – more info) I measured 400 mA current draw. That will kill a set of 2500mAh AA rechargeable batteries in 5hrs ish. Not to mention the beefier power electronics that are needed to handle nearly 1/2 amp continuously. (though as I write this, I’m beginning to think that maybe 5hrs may not be too bad. Assuming that the tool will be used 50% of the time, that puts the usage time at about 10hrs. That’s a day’s worth of shooting. Not outrageous.)

What if I take the AF assist module from the 540EZ flash, and shoot a defocused laser beam through it? I found a Ø 4mm laser module from DealExtreme and stuck it where the LED would go on the 540EZ AF assist module. The laser runs on 3v, and draws 25mA.

The pattern of the bare unfocused laser is just a splotch of light. When the AF assist module is added to the mix, a clean sharp pattern emerges.

The images shown above are the actual frame coverage at 50mm on a crop body (x1.6) Canon 40D. The pattern on the right has no problem getting the camera to focus a f2.8 lens in pitch darkness at 40ft away even on the external focus points (that aren’t cross type like the center one). A f2.0 or f1.4 lens should be able to focus with a much less intense laser power.

The pattern of just the defocused laser (on the left) will focus with the center point only, and it’s hit and miss, and takes longer to focus.

I may be onto something…