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COMMUNITY : FORUMS : PHOTOGRAPHY


Blue led photography...

I just took some new pictures for my BraceLED 2.0 I'ble. And look at the picture of the bracelet with the blue LED's! The reflection of the blue light on the white surface (=paper sheet) is highly overexposed!

How does this happen? Is the cmos sensor in my Nikon D300s over-sensitive to this color of blue? A picture of a red-led-bracelet under (almost) the same conditions has no such effect.

Picture red BraceLED: iso800, 35 mm prime, f/4, 1/20
Picture blue BraceLED: iso800, 35 mm prime lens, 1/15



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49
lemonie says: Oct 12, 2010. 1:49 PM
It's balance :you're throwing bright light onto a reflective-surface so you are getting bright-spots.

Software can blend different exposures, but I couldn't name any right now.

L
21
ynze (author) says: Oct 12, 2010. 2:14 PM
Do you mean HDR (High Dynamic Range) pictures? Never done that, but I guess it can be useful. Thnx!
49
lemonie says: Oct 12, 2010. 2:23 PM
I think that is it yes.

L
132
caitlinsdad says: Oct 12, 2010. 8:50 AM
Digital camera sensors can be more sensitive to parts of the light spectrum we don't see and will show up on the image. Being a "clear" LED may leave the light unfiltered. I know you can "see" the infrared coming off of a TV remote with a videocamera, probably a digital camera too.
3
NachoMahma says: Oct 12, 2010. 9:56 AM
. Plus the light sensors are often center-weighted. Since the center of the picture is dark, the iris is opened more (or whatever they do with digital cameras nowadays) and the bright places end up overexposed.
21
ynze (author) says: Oct 12, 2010. 12:46 PM
Thnx for the comments! The camera was set manually. Because of the strong contrast in the picture, I used a 55% grey card to measure the "light-strength" with the camera, using the "A"-setting (aperture fixed, the camera seeks an appropriate shutter-time). I set those values manually, and took the picture above.

changing the whitebalance K-value in the raw-file doesn't make the light spotes disappear...

I'll try to find the specs of the leds I used. Maybe they are emitting infrared or UV like crazy. After reading your comments, my guess is that the spots are UV-colored, because the red led's don't show the spots.
107
killerjackalope says: Oct 12, 2010. 10:51 AM
White balance and the method it uses to meter the exposure are likely the cause of this.

Try using manual settings.
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