George M. Anderson wrote:
> Paul;
> Sounds good. Thanks for the info. Now, where's my protractor ... <g>
> George
[...]
> >Yes, and my understanding is that the angle you need to exceed is 3
> >degrees.
> >The flash needs to be 3 degrees off the eye-lens line. The approximate
> >tangent of 3 degrees is 1/20, so the flash-lens distance should be
> >greater than 1/20 the eye-lens distance. (I'm the one who posted that.)
[...]
> >Paul Farrar
and David Russell wrote:
> I remember reading that red eye will occur when the flash/subject/lens angle
> is less than 15 degrees; I wish I could remember the source of this
> figure-perhaps Shipman himself?
> David
Hi, George, Paul, David and others,
I guess one could come up with a formula for red eye risk, but there are some
more factors involved: the diameter of the pupil (i.e. how dark are the
surroundings or what did she or he smoke), the diameter of the eyeball itself,
the angle of view of the person photographed (directly into the camera is
certainly worst, so it's nice to have sbd/sth to distract the photographed)...
In the endthen one should come up with a 'safe angle', which in turn can be
translated into a ratio of flash-to-lens to object-to-lens distances. If I get
my trigonometrics right, 15 degrees would mean an flash-to-lens distance of
roughly 1/4 of the lens-to-subject distance, requiring a 2,5m (8.2ft) wide
bracket at a distance of 10m (33ft)!!!
1/20 (3 degrees) sounds much better, but still, at 10m your bracket would have
to be 50cm (1.6ft) wide! Rather unwieldy, there must be a better solution.
BOUNCING does it of course, but at 10m (using medium fast film) the guide number
would have to be quite high to cope with the light loss. I guess, I could forget
my QA310 for that.
Do diffusors like the Sto-Fen and the like reduce the problem of red-eye? Is
there any other soulution (excluding pre-flash)?
Cheers,
Soenke, Hamburg
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