Need filter for White LED's

In message ,
"Jim" wrote:

What type of color correction filter do I need to remove the excessive blue
from white LED's. White LED's are pure white to the eye, but my camera sees
blue also.

I built a ringlight for macro use with my Olympus C-770 digital camera,
consisting of 24 white LED's, 20,000mcd each.

It works well, except for one hitch: the light the camera sees is blue.
Not a light blue caste but a medium blue when reflected from white paper or
cloth. My ringlight has 52mm threads, so I can use a 52mm filter between
the camera and ringlight, but I do not know which one to use.

I tried some of the yellow B&W filters I have, and they do reduce the blue,
but now everything is yellow. I know little about CC filters so need help
in selecting the right one.

The camera does not see the color balance that it gives you in its
files. All digital images are white-balanced, even ones in white light.
Depending upon your camera, and the exact color of the light, the light
color may be beneficial, or it may be detrimental. Obviously, you don't
seem to have a grip on white balancing. Your camera shoots RAW, so
shoot RAW, and you can white-balance in the RAW converter. If the red
and/or green channels look especially noisy, then you have too much
blue. Most digitals give the best images when the light has a purple to
magenta cast to it, if they output RAW or if the camera lets you do a
custom white balance.
--


John P Sheehy

In message ,
wrote:

In message ,
"Jim" wrote:

What type of color correction filter do I need to remove the excessive blue
from white LED's. White LED's are pure white to the eye, but my camera sees
blue also.

Another thing; it is possible that the LEDs don't have a continuous
spectrum, in which case many colors will come out a bit off. The "warm
white" incandescent-replacement flourescent lights you see, for example,
have a little notch in the blue area that makes it hard for me to tell
apart 2 color shirts I have, that are otherwise obvious, even in warm
setting sun.
--


John P Sheehy

What type of color correction filter do I need to remove the excessive blue
from white LED's. White LED's are pure white to the eye, but my camera sees
blue also.

I built a ringlight for macro use with my Olympus C-770 digital camera,
consisting of 24 white LED's, 20,000mcd each.

It works well, except for one hitch: the light the camera sees is blue.
Not a light blue caste but a medium blue when reflected from white paper or
cloth. My ringlight has 52mm threads, so I can use a 52mm filter between
the camera and ringlight, but I do not know which one to use.

I tried some of the yellow B&W filters I have, and they do reduce the blue,
but now everything is yellow. I know little about CC filters so need help
in selecting the right one.

Thanks
Jim

White LED's are pure white to the eye, but my camera sees blue also.


I have a white LED keychain flashlight and I can clearly see blue in
the light! Aimed at a white wall, the central part of the beam is much
bluer than the periphery. With light output like that, it would be
impossible to use simple filtration!

wilt wrote:

White LED's are pure white to the eye, but my camera sees blue also.



I have a white LED keychain flashlight and I can clearly see blue in
the light! Aimed at a white wall, the central part of the beam is much
bluer than the periphery. With light output like that, it would be
impossible to use simple filtration!

It might be a better idea to set a custom white balance in the camera
than to try and use a filter to compensate.
The problem may be that the output spectrum from a "white" LED is not
continuous, so there may not be enough yellow or red in the spectrum to
allow the camera to set a white balance from.
You might just have to put up with a blue cast in your pictures.

Hi Jim,

IMHO, the best way to work out what filter(s) you need would be to test the
light with a Konica/Minolta Colormeter or equivalent. These meters can tell
you which filters would best approximate a neutral result.

Cheers


"Jim" wrote in message
...
What type of color correction filter do I need to remove the excessive
blue
from white LED's. White LED's are pure white to the eye, but my camera
sees
blue also.

I built a ringlight for macro use with my Olympus C-770 digital camera,
consisting of 24 white LED's, 20,000mcd each.

It works well, except for one hitch: the light the camera sees is blue.
Not a light blue caste but a medium blue when reflected from white paper
or
cloth. My ringlight has 52mm threads, so I can use a 52mm filter between
the camera and ringlight, but I do not know which one to use.

I tried some of the yellow B&W filters I have, and they do reduce the
blue,
but now everything is yellow. I know little about CC filters so need
help
in selecting the right one.

Thanks
Jim

In message ,
"macropod" wrote:

Hi Jim,

IMHO, the best way to work out what filter(s) you need would be to test the
light with a Konica/Minolta Colormeter or equivalent. These meters can tell
you which filters would best approximate a neutral result.

A neutral result, however, is actually an arbitrary off-color to the
camera. Very few, if any, digital cameras are white-light native. The
vast majority give the best results (if they have RAW mode, or can
properly WB native light in auto- or custom-WB modes) if the light is
somewhere in the pink/magenta/purple range. Very often, the camera
wants something like 2:1:1.5 (R:G:B).
--


John P Sheehy

On Wed, 01 Feb 2006 07:33:41 GMT, wrote, in part:
In message ,
"macropod" wrote:

Hi Jim,

IMHO, the best way to work out what filter(s) you need would be to test the
light with a Konica/Minolta Colormeter or equivalent. These meters can tell
you which filters would best approximate a neutral result.

A neutral result, however, is actually an arbitrary off-color to the
camera. Very few, if any, digital cameras are white-light native. The
vast majority give the best results (if they have RAW mode, or can
properly WB native light in auto- or custom-WB modes) if the light is
somewhere in the pink/magenta/purple range. Very often, the camera
wants something like 2:1:1.5 (R:G:B).

But that would only make sense if the camera *really* is energetic about
its white balance corrections. If, instead, it allows the final image to
reflect somewhat the kind of light present, then images would look
pink/magenta/purple - even if they could be corrected to higher-quality
images than those took with white light.

John Savard
http://www.quadibloc.com/index.html
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In message ,
lid (John Savard) wrote:

On Wed, 01 Feb 2006 07:33:41 GMT, wrote, in part:

A neutral result, however, is actually an arbitrary off-color to the
camera. Very few, if any, digital cameras are white-light native. The
vast majority give the best results (if they have RAW mode, or can
properly WB native light in auto- or custom-WB modes) if the light is
somewhere in the pink/magenta/purple range. Very often, the camera
wants something like 2:1:1.5 (R:G:B).

But that would only make sense if the camera *really* is energetic about
its white balance corrections.

Could you rephrase that? That is making my head spin.

If, instead, it allows the final image to
reflect somewhat the kind of light present,

That's called "daylight" white-balance. It is truly a white-balance, as
white subjects in white light are literally green to cyan in most
digital RAW data, and the red channel has to be multiplies by about 2,
and the blue about 1.5, typically, for white in white light to be white.

then images would look
pink/magenta/purple - even if they could be corrected to higher-quality
images than those took with white light.

Yes, and that is the only reason I would shoot that way.

Case in point - I was out in the snow under overcast skies a couple of
months ago, with my 20D. I put a magenta filter over my lens, pointed
at the snow, and took an exposure. I then set this magenta snow as the
custom WB, and set the WB to custom. Then, (with the in-camera contrast
set to -2), I played with the exposure until the snow was just barely
clipping in the brightest spots. The shadows that resulted in tree
bark, etc, had very little chromatic noise, and no exagerated banding,
because none of the color channels needed to be multiplied very much in
the RAW converter.
--


John P Sheehy

On Fri, 03 Feb 2006 01:29:09 GMT, wrote, in part:
In message ,
(John Savard) wrote:

But that would only make sense if the camera *really* is energetic about
its white balance corrections.

Could you rephrase that? That is making my head spin.

.... if the camera will follow unreservedly its deductions from the scene
before it about how the scene is illuminated, so as to correct a scene
shot in even strongly colored light so that it looks as though it was
shot in a standard white light (presumably monochromatic light
excepted).

John Savard
http://www.quadibloc.com/index.html
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