Today I was doing research for another book idea, perhaps a sequel to The Undercover
. I was checking 3D red-cyan glasses just to provide an example of how some
materials absorb certain frequencies of light. To my surprise I discovered that more than
one web site seemed to be giving a very misleading explanation of how 3D glasses work,
giving a picture that shows red emerging from a blue filter, and blue emerging through a
red filter. So I sent an email to let them know... and this nice little debate followed:
Please note that the image from "how stuff works" explaining how the 3D glasses
work is incorrect. A red tint only lets red light through and a blue tint only lets blue light
Thanks for your concern. The arrows in the image
represent the image that each eye views.
Blue lens filters the blue and only allows that eye to see
red image and the red filters the red and only allows that eye to see the blue
That's not right. Blue filters let blue light through, and will block red images. Red
filters only let red light through. That's why the light appears blue or red through them -
they block all frequencies other than their colour.
If you don't believe me - try it. We have a red laser here that is blocked by a blue filter,
but passes through a red filter - as you would expect. The diagram is therefore
So explain How the decoder (Red) lens works: With your
idea when looking through red lens it would only see red image. Wrong! Red filter blocks
everything that is red in the image and only allows the blue hidden message to be reveled.
Or How the Wobble viewer works: Blue strip of film lets you see red image and red strip
sees the blue image. Works the same for 3d Anaglyph.
Test it yourself: Type the word red in red and the word
blue in blue on a white screen, look through the red lens, the only word you will see is the
By the way: You are the only one to complain in the 5
years it has been up. I did not create image, but copied it from another site.
OK, I did your experiment. Red written in red, blue written in blue. I look through a
red filter and I see the word blue more clearly. This is because the blue text is now darker,
the red text remains unaffected, and the white background has been filtered so that only
the red frequency comes through. The red filter blocks the blue light, making the blue
appear black. It lets the red light through unchanged.
So I repeat - a red filter only lets red light through, including the red of the text and
the red in the white background. It does not let the blue light through, which is why it
appears black. Same applies in reverse for the blue filter.
You are confusing light and dark here. As for why no-one else has complained... I
couldn't say. But I am a scientist, based in University College London :)
Okay. I accept that. When ever I get a chance I will fix
the image by changing the arrows (red to blue and the blue to red). I have not updated in 2
years and I am currently working on 80 2d to 3d images for one project due in 2 weeks
time. Doesn't give me time to keep up with web page. (Just 1 artist for - Glasses design, 2d
to 3d conversions, custom die -cut, lens effects, in house promotion, and web.)
Not your fault, William. I know the originator was howstuffworks.com. It's good of
you to be thoughtful enough to care.
Good luck with the 3D work, and thanks for a nice discussion.
And this is the incorrect diagram that seems to be confusing so many people. As I hope
you can work out, only blue arrows should emerge from the blue filter and red arrows from
the red filter. Watch what you believe!