Nikon CLS Tip: AF Assist Without Center AF Point

Funny how life works sometimes.  I did a hack to my camera's AF assist light to avoid buying an SC-29. But then shortly after that I saw a great deal on an SC-29 on ebay, so I got one (will blog about it soon).

Meanwhile, I was experimenting with the AF assist and I observed what I thought was a fluke.  Nikon's AF Assist works when the autofocus mode is either on Auto (the camera chooses the focus point), or when the center AF point is selected.  If a different AF point is selected, the camera's AF Assist doesn't work. 

I had assumed that the same was true for the SB-800, and all other accessories with an AF Assist light (the SB-900, SB-600, SU-800, SC-29, etc.).  Apparently, it's not true.  With these other accessories, the AF Assist light can work even when the AF point is not selected, depending on the focal length selected.  In fact, this is documented in the SB-900 and SB-800 manual (but not the SC-29 manual):

Another AF Assist tip: if you want to use only the AF Assist light but don't want to use the flash, there's an option in the SB-800 and SB-900 for that.  In the SB-800, go to the settings menu then scroll down.  Make sure the AF-ILL option is "ON" and the adjacent menu "Fire" is "Off".  In the SB-900 there is a similar setting in the menu for AF-ILL only.

AF assist light - stealth hack

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

THE PROBLEM:

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).


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

A SOLUTION

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).