Re: Red Eye, Again

[dthiessn@nslsilus.org (David Thiessen)]

Hi Physics Phriends,

First, I apologize for bringing up a subject that had apparently been
discussed recently on Phys-l or Physhare.  I didn't end my summer vacation
stop until winter break for reasons I'm too busy to tell and you're too
busy to read.

First, quoting me, Donald states:
> On Thu, 9 Jan 1997, David Thiessen wrote:
>
> > NOW HERE IS WHY I ASKED:  I have a domino mosaic picture of Einstein on the
> > wall up at the front of the room illuminated with fluorescent lights.  A
> > student took a flash photograph using a simple camera with outdoor color
> > film in it.
>
> You misled us. We thought you wanted to know about the human eye case.

It was not my intent to "misle" anyone.  I did and I do want to know about
the human eye case.  I wanted to confirm not only my explanation of human
"red eye" but that of the several physics and biology teachers here at
Deerfield and, apparently, our understanding of light reflecting off the
blood capillaries of the retina was correct.  AND I did not want to
complicate things by mentioning the Einstein domino "red eye" at the same
time.

If you had observed the reactions of teachers, having just explained human
"red eye", and then seeing the picture, you would agree that this was the
way to go.

I said:

> > When I asked the other science teachers here at Deerfield what causes Red
> > Eye, they gave the same "reflect off the red retina" answer. When I handed
> > them the photograph of the Einstein mosaic, they break out laughing.

Donald asks:

> So, why did they laugh? Did they suppose the two examples had anything to
> do with each other?

No, they knew that the two phenomena had nothing to do with each other.  It
was the incongruity of their red eye explanation and the surprise of what
they just saw in the picture which caused spontaneous laughter.  I'll see
how the physics teachers, both college and high school at the joint CAPO
meeting on Wed. at Elmhurst College react to the picture.

Then Donald asks:

> More information is in order. In the photos is the red on the black
> portions of the dominos, or on the white dots? (Use a magnifier.) I'd
> guess it's on the black.

You are correct. The black appears red only where specular reflection sent
the light of the flash directly back to the film.  We just lucked out that
the camera was aimed at the eyes.  Review: the picture was taken with an
instamatic type camera with outdoor color film using the flash in a room
bathed in 2500 watts of fluorescent light.  The greenish tint typical of
fluorescent lighting on outdoor color film is evident.

Donald then states:

> The University of Chicago has an excellent program in medical physics, and
> surely one of its faculty members could give you an authoritiative answer
> to the human red-eye question.

Right now, I'm satisfied with the explanations received from Phys-lers and
Physharers about human red eye.  My curiosity is about the picture.

Matt Tuley asks:

> I would love to see this picture, as would many of us I'm sure. Do you have
> access to a color scanner?

I am working on this:  We have a color scanner that is at least 5 or more
years old.  In computer hardware years (like dog years), this is like being
35 years old.  I used it a long time ago and was not impresssed.
Resolution was very poor.  I'll see what our Computer Tech people say
(although their first reaction is either, "No, we can't do that" or "Check
with the other guy).  I could probably get it done faster and better by
giving a student extra credit for a color scan of the picture.

I'll get back to you on this:

Bye,  David

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David  R. Thiessen                         FUN + PHYSICS = PHUN
Science Department                          PHYSICS IS PHUN !!
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dthiessn@nslsilus.org                 (Quote sources long forgotten)
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