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Old Jul 16, 2004, 6:02 AM   #1
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out of curiosity, how does the auto focus assist illuminator, like that found in the canon A75 for example, work to illuminate an area?

why can a camera with this feature take better dark pictures than a camera without one?

how does it help the flash? if at all...

is it just an LED that lights up before the pic is taken?

help a confused man out...thanks people...
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Old Jul 16, 2004, 6:15 AM   #2
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Redman wrote:
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out of curiosity, how does the auto focus assist illuminator, like that found in the canon A75 for example, work to illuminate an area?
In the dark the camera's AF system has a hard time seeing featureless objects... The AF illuminator usually works by projecting a set of contrasting patterns so that the camera's autocus system can pick up on.


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why can a camera with this feature take better dark pictures than a camera without one?
The camera does not take better picture... It's just a focusing aid. ie the camera only focuses better (or faster in the dark)


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how does it help the flash? if at all...
It does nothing if at all if a camera pre-flashes. The flash measurement is taken during the pre-flash for both exposure and white balance. If a camera does not pre-flash then the distance measurement resulting from the aid of the AF illuminator helps the camera modulates its flash output. :idea:


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is it just an LED that lights up before the pic is taken?
Most of the time... Some Canon has a brighter white beam as well which can double as a "red-eye" reduction system... :|


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help a confused man out...thanks people...
You're welcome!


Of course this is a generalization... Some cameras focus just fine in the dark without an AF illuminator. The A1/A2 are good examples of cameras that focus fine in total darkness, in fact they do this better than some cameras equipped with one. :?
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Old Jul 16, 2004, 8:32 AM   #3
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Agreed.

And others do not come with a red LED auto-focus assist illuminator. Some cameras, such as certain Canon models, use several smaller preflashesfrom the flashto aid in auto-focusing.
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Old Jul 16, 2004, 9:04 AM   #4
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Chako wrote:
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And others do not come with a red LED auto-focus assist illuminator. Some cameras, such as certain Canon models, use several smaller preflashes from the flash to aid in auto-focusing.
Did you turn this off yet? :-):-):-)

... This is probably the most useless feature I have ever seen: subjects end up with their eyes close more often than not. Try it the DRebel and 10D focus fine without it (unless you're shooting at a blank wall), beside it'll go easier on the battery
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Old Jul 16, 2004, 2:02 PM   #5
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Well, to explain how useful the AF assist beam is, you should know how the contrast detection focus works (in easy terms with pictures):
http://www.howstuffworks.com/autofocus3.htm

From that site you can see you need a certain amount of light for focusing to work, and without it the camera can't focus.

Of course it would be nice if all cameras used infrared focus assist beams, but visible LEDs are cheaper.
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Old Jul 16, 2004, 5:12 PM   #6
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I agree fully NHL. I always use the red assist beam from a dedicated Canon flash if the light is low.

When I read it in my manual, I just had to try it out. I went into a dark room, popped up the flash, and watched the stupid light show. What were they thinking?


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Old Jul 17, 2004, 10:20 AM   #7
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Some Sony digital cameras use a laser for focus assist. Sure seems like a neat idea to me...
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Old Jul 17, 2004, 11:32 AM   #8
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Wildman wrote:
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Some Sony digital cameras use a laser for focus assist. Sure seems like a neat idea to me...

There are limitations to that too. The camera evidently has to see a certain part of a pattern from the laser. If the pattern is broken up too much by the subject or not enough of the spots fall on the subject it can have focus problems. When it works it works well and it is reportedly almost perfect out to about 8 feet for people.

Maybe someone with a Sony holographic laser focus system could give better input. But I've read it isn't perfect.
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Old Jul 17, 2004, 11:00 PM   #9
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sweet, i understand now, thanks for all the answers guys...

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