Mickey -
In my experience, the incidence of "red-eye" is varied by a number of
factors, some of which are unique and variable by situation and
subject. In short, it's not something that can be practically or easily
calculated in ever circumstance.
You may know that "red-eye" is the result of light from a flash
reflecting off the retina of a subject's eye. It may seem as if you've
got a simple equation - flash to retina to lens axis. But don't forget
that the eye is an optical device itself, with it's own lens and
"aperture" system. The angles involved must fall within certain limits
before "red-eye" may occur of course, but they will be affected by other
factors even then.
The proximity of the lens to the flash is the primary factor - the
closer the flash is to the lens, the more likely "red-eye" will occur.
Other factors (albeit sometimes minor ones) are mechanical, such as the
focal length of the lens, the aperture set on the lens (a direct result
of the ISO/ASA of the film), and so on.
The other considerations are (for lack of a better term) biological.
Some people's eyes seem to be more prone to "red-eye" - their iris may
naturally dialate more than others, for example, or perhaps they focus
the light differently. Also, infants and (a-hem!) persons who have
subjected their bodies to alcohol, "drugs" or medications may exhibit
"red-eye" when others don't.
So if you're shooting with a different film, and lots of people are
using alcohol or other chemical substances, and you've got a new lens -
don't be surprised if Aunt Beth's photo makes her look like her eyes are
hot as coals!
That's why we all should move the flash _way_ off camera - better
cautious than regretful!
Just some observations based on my experiences....
Mickey Trageser wrote:
>
> John,
> I fully agree that low light levels are a major contributor to the redeye
> problem. But I have to wonder, how does the film speed/flash level play into
> this. Given a certain level of darkness and 2 film samples of different ASA,
> if the exposure is correct, wouldn't the proportion of reflectance from the
> retina to reflectance of the subject's face be the same? And wouldn't that
> net the same image level on the film? Of course, changing the f-stop would
> affect the depth of focus, and the shadow depth, but I suspect the redeye
> would be constant in intensity.
>
> Just my ponderings....
> -Mickey
> ----- Original Message -----
> From: "John A. Lind" <jlind@xxxxxxxxxxx>
> To: <olympus@xxxxxxxxxxxxxxx>
> Sent: Wednesday, October 11, 2000 2:11 PM
> Subject: Re: [OM] Red Eyes ????????????
>
> > I'm voting with Mickey. The first question that came to mind when I read
> > the original post was how much ambient light there was.
> >
> > Also, what speed of film were you using? If the light level was low and
> > you were shooting ISO 100 or 200 film, your flash was probably puting out
> > much more output making the risk that much more, and when it does happen,
> > it becomes much more noticeable.
> >
> > -- John
> >
> > At 21:11 10/11/00 , Mickey wrote:
> > >Luc,
> > >There are 2 factors to consider, one is the proximity of the flash to the
> > >lens. The closer it is, the more directly the light will be reflected
> from
> > >the subject's retina. If this hasn't changed, you might consider just how
> > >dark the room was. Many receptions I've attended are so dark that the
> > >people's iris's are wide open and normal flash mounting is too close to
> > >avoid the redeye. Often, even in the home, there is far more light to
> cause
> > >the iris to close down a bit than available in a wedding reception.
> > >
> > >I know this doesn't help win back your friend, but perhaps it helps
> explain
> > >how you could suddenly experience redeye.
> > >
> > >Mickey
> > >----- Original Message -----
> > >From: "Luc Chartrand" <chartrand_luc@xxxxxxxxxxx>
> > >To: <olympus@xxxxxxxxxxxxxxx>
> > >Sent: Wednesday, October 11, 2000 3:59 PM
> > >Subject: [OM] Red Eyes ????????????
> > >
> > >
> > >> I could believe my eyes, after taking around 10 000 pictures with a
> OM10
> > >for
> > >> 20 years now, I ad never encounter red eyes with my camera. This
> weekend
> > >I
> > >> was taking picture at friend (ex-friend !) wedding, and all the flash
> > >shots
> > >> add red eyes, WHY ??????????????????????
> > >>
> > >> The only thing that add to my camera this weekend was a Cross-filter,
> to
> > >add
> > >> the star effect.
> > >>
> > >> Please someone tell me the reason...........
> > >>
> > >>
> > >> Luc Chartrand
> > >> Hull, Québec, CANADA
> > >>
> > >> I'l wait for the answer before shooting my self ;(
> >
> >
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> >
> >
>
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