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BigDon
2007-Dec-19, 08:59 PM
Since the subject came up the other night while I was out admiring some of the fabulous Christmas displays folks put on in my part of the world I thought I'd ask.

Is there a real name (and explaination) for the "Peeping Tom Effect" when someone in a lit room thinks the curtain is opaque while folks outside in the dark are going "Whoa!" (or Yowza! as the case may be). I guess "the trick mirror effect" would be just as good a name.

Been wondering about that for a long time now. Living where I do, I get a lot of Latin American immigrants who don't realize that bed linens, while pretty, make really poor privacy screens at night. I keep meaning to tell them but something keeps popping up and I never get around to it.

(Hey, I'm not a skulker, if I can see your business while strolling down the sidewalk, the fault is elsewhere.)

grant hutchison
2007-Dec-19, 09:19 PM
It's a contrast thing.
If you have a partially reflective, partially transparent screen between a dark room and a bright room, folk in the bright room will see their own bright light reflected off the screen, largely washing out any detail in the darkness beyond.
Those on the dark side will have no reflected light on their side, and will see the "signal" shining through from the bright side with little interference.
The same logic applies whether the screen is a partial scatterer (like a net curtain) or a partial reflector (like a half-silvered mirror).

Grant Hutchison

a1call
2007-Dec-20, 02:40 AM
Why start a new thread when I can hijack this one? :)

On a somewhat related note, ever take a picture at night, in a bright room and notice that the glass window is reflecting much more in the image than what you see with unaided eye.
Why things like glasses and plastics seem to have a higher reflection rate when being looked at through a LCD viewfinder?
I am sure that others have noticed this too as the effect is very prominent.

01101001
2007-Dec-20, 03:10 AM
Why things like glasses and plastics seem to have a higher reflection rate when being looked at through a LCD viewfinder?


My large guess: glass reflects infrared, and the CCD is more IR-sensitive than your eye. See if your viewfinder brightly shows an IR TV remote shot into it.

a1call
2007-Dec-20, 03:46 AM
Good point 01101001,
Yes I can see my remote's LED blinking through the viewfinder.
I think the difference might also have something to do with the electronic image having a higher contrast than an unaided eye.
It got me thinking how different from one another we might all be perceiving a scene.

Added: On a somewhat related note to the somewhat related note: :)
Through a LCD viewfinder, A red LED would look red, a green one green, a blue one blue.
Shouldn't an IR LED look perhaps reddish?
Why does it look white?

Nowhere Man
2007-Dec-20, 11:31 PM
Added: On a somewhat related note to the somewhat related note: :)
Through a LCD viewfinder, A red LED would look red, a green one green, a blue one blue.
Shouldn't an IR LED look perhaps reddish?
Why does it look white?

I'll give this a shot. The CCDs in the camera are purely monochromatic. They have little red, green, and blue filters over them to keep out the unwanted colors. CCDs are also sensitive to IR. I'd bet that the incoming IR punches right through the filters with equal ease, thus giving a level 3-color signal, producing white.


Fred