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How far can this lens "see-through"?

Dave Martindale
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"J. Clarke" <(E-Mail Removed)> writes:

>The fabric isn't all that special. Ever have a 16 year old ask you not to
>use nightshot mode on a Sony camcorder because her Daddy shot her 15th
>birthday that way and "it was embarrassing"?

What matters is the IR absorption properties of the dyes used on the
fabric. "Black" fabric may absorb only visible light while passing IR
freely (apparently typical of organic dyes), or it might absorb all
frequencies of light.

The dyes used in colour film pass IR pretty freely; that's why it's not
safe to look at the sun using any number of thicknesses of colour film
stacked together. (Not much visible light gets through, so your eyes
don't blink or squint, but most of the IR is still getting through and
will cause damage). That's also how film scanners with "ICE" work -
they make a 4th pass using IR light, and the image dyes are transparent
in IR but dirt and scratches appear dark.

On the other hand, the metallic silver in B&W negatives does absorb IR,
and so does carbon black in ink, so these are opaque even in IR.

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