On 14/06/2011 12:46 PM, Igor Roshchin wrote:
Tue Jun 14 13:48:28 EDT 2011
John Francis wrote:
On Tue, Jun 14, 2011 at 11:03:41AM -0400, Igor Roshchin wrote:
Hi All!
After taking photos at a party, I discovered an interesting effect.
It was indoors, with uneven and not very bright light, so, I used
a flash bounced from the ceiling, which made the light rather uniform.
[ . . . ]
I suspect, that this particular color (dye) fluoresces from the flush,
or something like that.
Quite likely - dyes (or pigments) used to colour plastic items often
have significant response to ultra-violet light. Even if they don't
fluoresce, the output from a flash can produce quite a bit of UV light,
and sensors "see" further into the UV than does the human eye.
You could try using a UV filter on either the camera or the flash.
John,
Even though purple might have an mixture of blue/violet with red,
I would expect that purple would be farther on the spectrum and closer to
the violet part than blue.
That would mean that hitting the violet (or UV) part of the spectrum
should shift the color toward violet, not toward blue.
Igor, filters aren't all that spectrum specific, and tend to be cut
filters, in that they don't pass any spectrum below a particular
wavelength (which will vary from filter to filter).
UV florescence has been a problem since the dawn of electronic flash. A
lot of things reflect a disproportionate amount of UV light.
This is especially true of man made fabric materials (nylon, rayon,
satin, and the like and make up.
My wife has a lovely emerald green gown that photographs blue with
flash, and bluey green under daylight, for example.
A wedding I shot many years ago ended up being an epic fail because the
bride and bridesmaids ended up pooling their make up resources, and
probably used half a dozen different brands of product.
They looked gorgeous, but the flash pictures showed all sorts of
blotches and zebra stripes where make up brands met each other.
--
William Robb
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