UV filter
Dec 16, 2018 17:32:55 #
User ID wrote:
I think you missed that he's filtering at the light source to
reduce phosphoresence. He did not mention lens filtering.
Not sure what the actual light source is, but hopefully it's
not strobes. Filament lights, or perhaps tungsten balanced
LED, would put out far less UV in the first place than xenon
tubes !
.
reduce phosphoresence. He did not mention lens filtering.
Not sure what the actual light source is, but hopefully it's
not strobes. Filament lights, or perhaps tungsten balanced
LED, would put out far less UV in the first place than xenon
tubes !
.
You're right, I did not read carefully enough.
However, the last two sentences of my post could still provide some useful information.
Dec 16, 2018 19:12:19 #
larryepage
Loc: North Texas area
canon Lee wrote:
I do studio shoots for youth sports clubs where on... (show quote)
Try directing your light through a couple of thicknesses of plain window glass. Glass is a very good UV filter. If that doesn't work, laminated automotive glass might work. It was an old rule of thumb that a quarter inch of glass would remove 95% of UV from sunlight.
It is noted above that various types of discharge lamps, including xenon strobes, can be rich in UV. "Hot" lights, (incandescents) tend to be richer in IR, with much less UV.
Dec 21, 2018 10:54:44 #
User ID wrote:
I think you missed that he's filtering at the light source to
reduce phosphoresence. He did not mention lens filtering.
Not sure what the actual light source is, but hopefully it's
not strobes. Filament lights, or perhaps tungsten balanced
LED, would put out far less UV in the first place than xenon
tubes !
.
reduce phosphoresence. He did not mention lens filtering.
Not sure what the actual light source is, but hopefully it's
not strobes. Filament lights, or perhaps tungsten balanced
LED, would put out far less UV in the first place than xenon
tubes !
.
Hi I just hopped over to the alien bees mono light, which I use, and this is the source; Flashtube
14mm flashtube (daylight-balanced and UV-coated) seems to me that I've only added more uv protection with the uv sheets. The bottom line is that I still get hot spots on the glow shirts and have not found a way to eliminate them...
Dec 21, 2018 16:08:28 #
canon Lee wrote:
The bottom line is that I still get hot spots on the glow shirts and have not found a way to eliminate them...
After digging into this a little more: some fluorescent dyes absorb blue or violet visible
light and then emit orange or red visible light.
The Light Spectrum and its Relationship with Fluorescence
https://www.thermofisher.com/us/en/home/life-science/cell-analysis/cell-analysis-learning-center/molecular-probes-school-of-fluorescence/fluorescence-basics/fluorescence-fundamentals/light-spectrum-fluorescence.html
There's nothing you can do about that except put a yellow gel over your flash unit and convert the image to B&W (or shoot B&W film).
Dec 21, 2018 16:47:00 #
For anyone who's interested in a low-cost UV gel for flash tube: try spraying a sunscreen product
on a clear gel and placing it over your flash. Pick a non-greasy formulation with an SPF rating of 50 or
better that also blocks UVA(SPF testing only measures UVB).
A substance is said to "fluoresce" if it emits visible light of a lower wavelength after absorbing
light of a higher wavelength. For example, if it emits visible light when exposed to UV light.
As you know, some inks and dyes are deliberately formulated to fluoresce in sunlight, in order to
make them look brighter Some glow only n short-wavelength UV, some only in long-wavelength UV,
some in violet or blue visible light.
To make UV filter testing easier, it's helpful to collect samples of objects that fluoresce brightly.
A black light is helpful in finding such objects. Longwave (UVA) "blacklights" are the most common
and safest. Shortwave (UVC) lights are also available (but require protective eyeware). Both kinds
are used for indentifying rocks and minerals. (UV protective eyeware usually appears yellow tinted
under visible light.)
Fluorescence is most familiar and has been studied the longest in connection with rocks and minerals
(going back at least to George Gabriel Strokes in 1852 -- who named the phenomenon after the mineral fluorite
= calcium fluoride -- the same substance used by Canon for elements in its 'L' camera lenses). Unlike commercial
products, minerals don't get reformulated or taken off the market:
https://geology.com/articles/fluorescent-minerals
There are different bands of UV light. By wavelength:
UVA 400 nm - 320 nm longwave blacklight lamp
UVB 320 nm - 290 nm mediumwave UV
UVC 290 nm - 100 nm shortwave blacklight lamp (minerology)
Not all UV filter materials absorb all UV bands.
The famous "ozone layer" in the Earth's atmosphere absorbs
almost all high-energy UVC and most UVB from the sun. It is less
good at absorbing UVA. Unfortunately, your flash is not equipped
with an ozone layer.
A Xenon flash tube doesn't emit much UVC--it's not hot enough.
But it emits a lot of UVA.
https://www.heraeus.com/media/media/hng/media_hng/what_do_you_want_to_do/Xenon-output-spectrum.jpg
NASA Science Mission Directorate: Ultraviolet Waves
https://science.nasa.gov/ems/10_ultravioletwaves
NASA: "Ultraviolet Light"
https://www.nas.nasa.gov/About/Education/Ozone/radiation.html
on a clear gel and placing it over your flash. Pick a non-greasy formulation with an SPF rating of 50 or
better that also blocks UVA(SPF testing only measures UVB).
A substance is said to "fluoresce" if it emits visible light of a lower wavelength after absorbing
light of a higher wavelength. For example, if it emits visible light when exposed to UV light.
As you know, some inks and dyes are deliberately formulated to fluoresce in sunlight, in order to
make them look brighter Some glow only n short-wavelength UV, some only in long-wavelength UV,
some in violet or blue visible light.
To make UV filter testing easier, it's helpful to collect samples of objects that fluoresce brightly.
A black light is helpful in finding such objects. Longwave (UVA) "blacklights" are the most common
and safest. Shortwave (UVC) lights are also available (but require protective eyeware). Both kinds
are used for indentifying rocks and minerals. (UV protective eyeware usually appears yellow tinted
under visible light.)
Fluorescence is most familiar and has been studied the longest in connection with rocks and minerals
(going back at least to George Gabriel Strokes in 1852 -- who named the phenomenon after the mineral fluorite
= calcium fluoride -- the same substance used by Canon for elements in its 'L' camera lenses). Unlike commercial
products, minerals don't get reformulated or taken off the market:
https://geology.com/articles/fluorescent-minerals
There are different bands of UV light. By wavelength:
UVA 400 nm - 320 nm longwave blacklight lamp
UVB 320 nm - 290 nm mediumwave UV
UVC 290 nm - 100 nm shortwave blacklight lamp (minerology)
Not all UV filter materials absorb all UV bands.
The famous "ozone layer" in the Earth's atmosphere absorbs
almost all high-energy UVC and most UVB from the sun. It is less
good at absorbing UVA. Unfortunately, your flash is not equipped
with an ozone layer.
A Xenon flash tube doesn't emit much UVC--it's not hot enough.
But it emits a lot of UVA.
https://www.heraeus.com/media/media/hng/media_hng/what_do_you_want_to_do/Xenon-output-spectrum.jpg
NASA Science Mission Directorate: Ultraviolet Waves
https://science.nasa.gov/ems/10_ultravioletwaves
NASA: "Ultraviolet Light"
https://www.nas.nasa.gov/About/Education/Ozone/radiation.html
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