This is a bit of an odd question, but bear with me. You know those big red AF-assist LEDs in external flashguns, and older built-in flashes? Well what kind of league is the radiation from those in. Talking to one of the sales assistants in my local, friendly, usually extremely clued up camera shop (EOS specialist centre)about an entirely different subject [close-up flash and AF] I mentioned the big red light on the front of my flash (Sigma EF-430 ST) "Oh no, you only see that very rarely" he said "it's infra-red" Not wanting to argue, I decided to let it pass, but now I'm intrigued.

I know that on my compact, which uses infra-red to gauge the distance for focusing, I can occasionally see the near-infra red beam if I get the angle right. I got my camera, an EOS 1000F 2nd hand, and I also got an unofficial Hove Foto users' guide. This mentioned an infra-red AF-assist light on a Canon Flash unit. Previusly I had just assumed that flash units had a normal run-of-the-mill red LED behind that big lump of translucent plastic, but now I'm not so sure.

So now, if you've got this far, I present my question. Is the BASIS AF sensor in the EOS 1000F sensitive to infra red, and if so, what wave lengths? I'm wondering if I can rig something up with an infra-red LED that emits wavelenghts *outside the visible spectrum*, or a tiny LED torch called a Photon, to help me focus with the appallingly low light levels I get with my extension tubes. This may be a stupid question, but I thought I'd ask anyway, to see if anyone has any idea what I'm going on about. Thanks.

-- David Miller (david_miller@btinternet.com), February 27, 2002

Answers

I understand your question but I don't really have an answer. However the AF assist lights in Canon Speedlites and Canon camera bodies are a deep red (commonly called *near* infrared). They all emit visible light.

I also know that most optical slave devices are sensitive to true IR light. You can use Wien or Vivitar's IR slave triggers to trip them off very easily, and (at least with the Wien unit) you can't see the light at all. I suspect that most AF sensors are like the slave sensors and not limited to our visible spectrum of light. So your idea would probably work.

You ought to try it & report back with your findings.

-- Jim Strutz (j.strutz@gci.net), February 27, 2002.

put a 87-series (blocks all visible light, but let's infrared trough) filter over the assist-beam, go in a completely dark room. and try to focus on a well. there's your answer.

-- m. lohninger (anavrin@mac.com), February 27, 2002.

well = wall!

-- m. lohninger (anavrin@mac.com), February 27, 2002.

The AF-assist is never infrared. It is plain red light. If it was infrared, the AF would be off. Those who have shot infrared film would have experienced the focus shift with IR light rays, and that you have to refocus before shooting (the image will actually look unfocussed in the viewfinder). Most people who claim it's "infrared" AF-assist are clueless.

-- Anthony (doom_metal@hotmail.com), February 28, 2002.