This week we have a question for anyone who has ever taken a
photograph, as Ferrettbadger asks:

Why do you get 'red-eye' in photographs?

A nice, simple question, but does it have a nice, simple answer?
Regular readers will be amazed to hear that... well... yes, it
does.

The winner¹ was E G
Mel, who provided this explanation:

It's to do with the reaction speed (or lack of) of the iris to the
flash. When you are indoors, especially pubs etc, it's quite dark, so
the iris in the eye is wide open allowing in as much light as
possible. However, when the camera flashes, the iris doesn't have time
to close and the light reflects off the back of the eye producing the
red effect.

Some additional clarification was added by Orcus, who pointed out that:

It's red because there are blood vessels close to the surface of
the retina, from where the light rebounds.

Also chipping in was Ste, with a comment
on how modern camera design contributes to the problem:

Also on these tiny new digital cameras the flash bulb is
often closer to the lens than on older cameras, or SLR cameras. The
chance of getting a (red) retina reflection hitting the lens is
greater.

And it's not just the camera that can make it worse. Your subjects
may not be helping themselves to look their best, as Mel observes:

It should also be noted that the more alcohol consumed, the slower
the reaction of the iris and the more red-eye there is in
photos!²

Not that this is likely to be relevant to any of the readers of
SEx Education, of course...

Make It Go Away

So now that we know why it happens, what can we do about it? Well,
camera manufacturers are trying to help, as Mel explains:

This is why many cameras have a red-eye reduction mode, which
either does two flashes - one to close the iris, the next to light the
scene - or a prolonged period of light just before the main flash to
produce the same effect.

Of course, this doesn't always work in quite the way it's intended;
at least, not for Ictoan it doesn't:

You don't get red-eye but you do get everyone with their eyes
closed or half-closed looking stunned and rather, well, not
flattering!

Hmm... perhaps not. What else can we try?

Another trick is to have the people being photographed look near
the photographer, rather than straight at the camera. I've seen
photographers hold up their hand to have people look at that.

A useful tip from Arnie Appleaide
there, who also notes that this technique "jibes with the above
theories - if your eye isn't aimed straight at the lens you can't
reflect the light back into the camera".

Finally, DrMatt observes that, "the most
invariably effective way to eliminate red eye in photographs is to
develop cataracts"³.

So there you have it. We know why red-eye happens, and we have some
useful tips for preventing it. So what's missing..? Ah yes, the
downright silly answer:

It could be a sign that you are possessed by
demons 
- Researcher 179541

This article was based on a conversation at the SEx forum - where science is explained.

Why not pop over with your own questions? The pick of the bunch
will feature in The Post's next
issue.

SEx Education Archive
Archive

Danny B.

22.02.07 Front Page

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