Re: EOS: IR & IS in TC: WAS Canon's Infinite Wisdom

[Gary Beasley <beasleyglb@xxxxxxxxxxxxxx>]

At 04:00 PM 1/15/98 +0000, you wrote:

ting." 
>
>Btw, as an IR photographer I am a bit disturbed by the fact that
>they mention the use of  " IRED's " (InfraRed Emitting Diodes) for
>detection of the actual IS lens group position. 
>
>The core question: Is there any other advantage to IR LED's than that
>they are not visible? If being not visible is the only reason, then I
>can assume that Canon at least thought it *possible* that visible
>light made it into the final image, if not very *likely*?....hence
>they did not *want* to use visible LED's? 
>
I think it more likely that IR leds have been the industry standard for
position sensors for a very long time, as IR leds were among the first to
be developed and have a very long lifetime and low power requirements. The
sensors in the lens body would likely be reading a reflective surface on
the side of a lens element and not be aimed directly down the optical path.
If you want to know for sure get a video camera and look at the lens with
it. The IR beams will show up as white lights.
Gary Beasley
beasleyglb@xxxxxxxxxxxxxx
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