AF assist beam

[chetanvala]

Hi,

Can someone help me clear this up. I have written to Canon and gotten a response, but it didn't quite answer my question or I didn't understand it!

Anyway this function is the AF-Assist Beam, now on some of your Point-And-Shoot cameras you have what I would expect to be this function. Whereas I am taking this to be, when you focus on a subject a physical beam is Emitted - As the function name suggests

I.e I am expecting that I should see a little red/green dot or whatever on the actual subject. I am using the Camera in "TV" or "AV" mode so as to deliberitely not be in one of the basic zones where a lot of the Custom Functions are not active (I think).

But I'm afraid the manual doesn't really shed any light on it - Forgive the pun!

What I want to know is:- Should I see a little dot on the subject when I am focusing - When this is set to "EMITS".

If not then what the hell does this mean? Sorry if I sound stupid but I am a novice!

Thanks Guys
originally posted.. SAME QUESTION...

[inkista]

No, you won't see a dot on your subject. It isn't a laser sight.

The AF assist lamp basically throws out patterned light so the camera's autofocus system can more easily lock focus in low light. Most of these systems use contrast detection, and when the light is low, there's not enough contrast for the AF system to distinguish focus. The AF assist lamp throws out more light to help the AF system "see" better. Typically, what you'll see (if visible light is being used) is a matrix-type pattern.

My ST-E2 throws out a grid of red light for AF assist.

[OsmosisStudios]

The extra flashes use an LED grid light: your body may or may not have this function (depends on the body). The body alone hwoever uses a simple light emitted from the camera.

If we look at the 40D, for instance:


The AF-Assist light is the small white circle to the left of the CANON logo.

[Bryson]

Should we enable it in our Canon DSLR?

[inkista]

Depends. If you don't actually need it because you have enough light, and it's annoying your subject to have the AF assist lamp blinking at them all the time, then, no. If you're shooting caverns while spelunking, then yes. That's why you have the choice of turning it on and off as needed.

[Doug Pardee]

Originally Posted by OsmosisStudios

If we look at the 40D, for instance:


The AF-Assist light is the small white circle to the left of the CANON logo.

No, that's the red-eye reduction light and self-timer indicator. AF assist is the big thing sticking up at the top (the pop-up flash). It'll rip off a quick series of low-power flashes, which probably nobody in the known universe likes.

If you have an external flash mounted, it will have its own AF assist beam that will be much nicer.

[OsmosisStudios]

Originally Posted by Doug Pardee

No, that's the red-eye reduction light and self-timer indicator. AF assist is the big thing sticking up at the top (the pop-up flash). It'll rip off a quick series of low-power flashes, which probably nobody in the known universe likes.

If you have an external flash mounted, it will have its own AF assist beam that will be much nicer.

There's no such thing as a Red-Eye reduction light: that's all in how the flash fires. If all that is is a self-timer indicator, then Canon needs to redesign their cameras.

[Photostudent]

Originally Posted by OsmosisStudios

There's no such thing as a Red-Eye reduction light: that's all in how the flash fires.

Doug is indeed correct in stating that the small light on the Canon is a red-eye reduction light/self timer indicator. Nikon has a similar light that is slightly larger that is used for focus assist.

chetanvala - Canon uses the pop-up flash for auto focus assist. Make sure you have it "popped" if you need to focus in low light. I don't think it pops up automatically unless you are on one of the auto scene modes or full auto. You will notice the flash strobing if the light is too low to lock focus on the subject

[OsmosisStudios]

Originally Posted by Photostudent

Doug is indeed correct in stating that the small light on the Canon is a red-eye reduction light/self timer indicator. Nikon has a similar light that is slightly larger that is used for focus assist.

You'll have to provide a quote from the manual: theres no such thing as a red-eye reduction light.

[Photostudent]

Hi Osmosis...

You must be a true Nikonian Even though I am currently a Nikon user myself, I was (and still am to an extent) a Canon fan.

Canon likes to use this little lamp for red-eye reduction and self timer indication on most of their range. They also have a little indicator in the viewfinder that indicates when the red-eye light is on.

Please refer to p16 of the following Canon D40 manual.
http://www.canon-eos-40d.com/Canon-EOS-40D-Manual.PDF

or see the last paragraph in the following quote from Canon's own online Digital Learning Center at Canon Digital Learning Center - Red-Eye in Flash Photos

Red-eye Reduction:
The idea of this feature is that by one means or another, the camera sends out light to your subject before the picture is taken. Since the subject’s pupils normally tend to dilate, or get wider, in dim light (and get smaller in bright light conditions), the idea is to reduce the level of red-eye by making the user’s pupils appear smaller before the picture is taken.* With smaller pupils, there’s less area to be marred by red-eye, and even if it does show up in your pictures, it’ll tend to be less noticeable.
Some cameras do this by rapidly flashing the flash unit with "pulses" of flash illumination, for a second or two before the picture is taken.* The hope is that your subject’s eyes will react to these rapid pops of light and the pupils will become smaller.* A moment later, that actual picture is taken, with the flash firing again, but at (usually) greater power.
Canon’s cameras take a different approach, using a small, built-in lamp to shine continous white light directly at your subject for about two seconds, prior to the picture being taken.* In fact, a scale appears on EOS digital SLRs with this feature in the viewfinder, to count down the two seconds that this red-eye reduction lamp is active, so that you know when to fully press the shutter button and take the picture.* Again, the idea is that this added light before the picture is taken will cause the subject’s pupils to contract, and therefore reduce the level of red-eye if it appears.