None of the Canon cameras turn on the AF assist light (the red light) on external flashes continuously after focus has been achieved.
I’d like to stick a laser pointer (one that projects a pattern) in the flash slot and paint the subject with some sort of laser light pattern to give the AF sensor something to easily focus on. This way, if the laser light is on continuously, then I can use the AI Servo mode to continuously track the subject in low light situations.
In order to turn on/off the laser pointer, I will use the top left most small pin off the flash hot shoe (not the big round one). See diagram in this thread.
Canon hotshoe pinout description here.
I may have to tweak the diagram shown in the link to turn on the laser pointer, but it should be doable.
The beauty of using the signal off the hot shoe connector is that it comes on only when the camera needs to focus, and stays on only for 7 seconds after it’s done focusing, or 3 sec after the shutter is fired.
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Update: 20 Sept 2010
I went to Club neutral last night and shot some pictures there. (Description of results from that night’s shooting at this post) I took the laser pointer with me, but I could not reliably use it. I had no mount for it other then the velcro I brought with me, which couldn’t keep it in one place especially when having to push the button all the time to trigger it.
When leaving the club noticed a red led bike light, and thought it may work for me too. Tried the red led bike light I have, to see how well it would assist the camera in focusing. Compared to the AF assist light from the Sigma EF500 DG super flash, it took almost twice as long to focus, and at times the bike light didn’t even acquire focus. So much for a simple solution.
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UPDATE: 24 Sept 2010
Came across a few forum posts where people are discussing AF assist lights. This chinese site has an interesting idea.
Also this forum and this forum have discussions on AF Assist lights.
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UPDATE: 02 May 2011
I have progressed this project further. Check out this post for a working laser AF assist tool.
I was reading the (long-dead) FM thread with the idea of having the light go on with half-press and momentarily shut off for exposure. It’s a great idea but my EE skills are non-existant.. and combining those 2 circuits even more out of my league.
Did you make anything?
I love the idea. I shoot nikon so I would have to grab the pinout for my hot shoe plate. but basically I was thinking about the same thing. I want the functionality of my remote flash set up with my sb600 and d90 and d7000 but I don’t want to be tethered by a cord. So like you with club shooting you just need something to focus on. If my AF assist light on my SB600 would turn on while off camera I would be set without waiting for the flash to sync with the camera’s af assist. I was just now thinking instead of reinventing the wheel maybe the thing to do would be to find a way to key the AF assist light on the flash instead. If you have the pin out then maybe there is a work around for that.
With the laser there still remains the problem of attaching it and turning it on and off.
@Vaizki, I never ended up making anything.
@Muhammed, the challenge I’ve had with using the AF light on the remote flash is the alignment of the AF light with where you’re focusing. I found it nearly impossible (in my shooting) to consistently have the AF light of the flash be pointed where the lens/AF point is looking.
I have opted for a different approach: use an existing flash controller with AF assist light ST-E2 (I don’t know if Nikon makes an equivalent unit) and attach a cord for off camera flash. See this post:
http://adrian.onsen.ca/2011/01/adding-remote-extension-to-a-st-e2-flash-commander/
This setup has worked very well for me for me since I made it. The AF light is always pointed where I need it (where the lens is looking) since it’s on the camera, and the flash can be pointed/bounced off anything as I don’t need it’s AF light.
The ST-E2 controller is purely used for it’s AF light. For a next project I’m going to integrate a wireless flash trigger to the controller, to also allow me to control long distance flashes.
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