Thursday, September 9, 2010

AF assist light - stealth hack

Here's a simple modification to a camera's AF assist light to make it less intrusive.


Many cameras have a built-in autofocus assist light to help the camera focus in low light situations.  I find it very useful - there's no doubt that it works.  But sometimes it's annoying when you're trying to maintain a low profile.  It also causes many people to blink.

Meanwhile, some external flashes also emit an AF assist light, but one colored red, which is both less intrusive, and (in my experience) much less likely to cause people to blink.  However, I like using my external flash off-camera, and using it that way disables its AF assist light.  This was enough reason for me to think about getting an SC-29 (a Nikon TTL cable that has a component that emits a red AF-assist light).
SC-29 Ttl Coiled Remote Cord

The SC-29 is not cheap though, so I tried to find another way.


I thought, why not use a gel to simulate the less intrusive red AF assist light of an SC-29?  I have the Rosco sampler pack and found a gel that looked close enough to the red color that I wanted - Rosco #2001 Strato Red.

I cut a small piece and tested it with my AF assist light.  It worked - both in terms of being less intrusive and maintaining AF accuracy and speed.  It was still fairly bright compared to the AF assist light from an external flash, so I tried doubling it up (by folding it), and it still worked.  The light was now dim enough to be similar to that of an external flash.  I trimmed the edges, then used Scotch double-sided tape to keep the gel folded together and to stick it over my camera's AF assist lamp.  It's not a perfect solution because the AF assist lamp on my camera is rounded, and the double-folded gel isn't flexible enough to conform to the lamp's shape, but I think it will stay there.

Incidentally, I also tried an infrared filter, but it didn't work.  First, the camera had a hard time acquiring focus, and even when there was focus confirmation, the image was out of focus.  Second, the lamp was more noticeable.

BTW, you may be wondering how I took the photo of my camera.  I used an old compact point and shoot, the Casio Exilim EX-V7 using bounced flash, something I will post about soon. :)

UPDATE: I tried to see the range of the AF Assist light with the red filter, and it appears that the camera can focus as far as 15, if not 20 feet (even though the specs say the AF assist is good for up to 10 feet).


  1. Hello
    You amaze me again with your energy
    If you shoot close portraits …your tick is super.
    In the same time, the gel is reducing by 1 stops( very imprecise number ) the light so the the Af assistant will work for a shorter range.
    Also the AF assistant may work more time(overheat) and go on stand by to cool .
    Regardless the limitations I believe your trick is useful for specific applications.

  2. Hi Robert. Your point about range reduction is absolutely legitimate and was a bit of a concern for me as well initially. However, when I tested it last night I didn't notice a reduction in range, at least for my camera (D300). I focused just as quickly as I normally do at 10 ft (the range that the camera manual gives for the af assist light). I will test tonight to see how far I can focus. I suspect 15 ft is possible. If the range is shortened too much I would switch to a single layer of the gel.

    As for the overheat issue, that's interesting. I didn't know the af lamp could shutdown to cool. So far though, with my former d80 and my d300, after 15k shots or so I've never seen it happen, and never felt the af assist lamp to be warm. Maybe my cameras use LED? Anyhow, I focused just as quickly with or without the gel, so I think the risk of overheat for my camera seems about the same as without the gel.

    Best regards,

  3. I just chanced upon this blog and reading some material here. Very useful.

    Regarding this mod I am now wondering if a red colored transparent sharpie/ink or some such will do the trick. I will try it out sometime.

    1. Glad you find the blog useful. :)

      About the sharpie it might work... Please post either way. Thanks!


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