If you photograph a grey or white card, are you able to completely correct the blue colour cast the leds give ? In other words, if you hover an image editor colour sampler icon over the white or grey areas, can you get the RGB values more or less equal to each other ?
Finally found time to test the white balance (WB) characteristics using this ring light. I used my SX20 IS for the test. I tested different scenarios: with the WB set to Auto WB (in daylight only), using a "White" card and using a DGC-100 Digital Gray Card (from Robin Myers Imaging). I shot using DNGs to compare JPG vs DNGs. This was a multi-step process because I wanted to compare results with this particular camera and abilities of the ring light.
Daylight (cloudy day)
- Tested with white card to setup the custom WB
- Tested with gray card to setup the custom WB
- Tested with Auto WB (AWB)
Ring light
- Tested with white card to setup the custom WB
- Tested with gray card to setup the custom WB
Testing results
1 - WB comparisons daylight vs Ring light. Overall, the daylight custom WB and ring light custom WB compared favorably as long as the white card was postioned close to the focal plane of the object (see note that follows) and you used fresh batteries. The custom WB resulted in better color rendition than my original photos when I used the camera's built in "daylight" setting. Since I didn't design this setup to be used with an AC power source I wasn't able to test the effect this might have, however I would expect an AC power source to perform more reliably.
2 - Custom WB setup when using Ring light vs distance to object. During the setup of the custom WB using the ring light it is very important to place the white card relatively close to the focal plane of the object you will be shooting. Color variances that occurred at different distances from the lense was noticeable and had an effect on the WB. Since the light source isn't as strong as commercial ring lights, this is a trade off with this setup.
3 - Determine the best way to set the custom WB on the SX20. The SX20 Camera Users Guide recommends using a "white" card to set the custom WB. I compared these results with the gray card and Auto WB (AWB) of the camera. The white card resulted in the best color rendition, followed by the AWB. The gray card tended to render a warm tone (slightly off white) results. Conclusions: a) Definitely use a white card for this camera 2) daylight conditions can vary enough that setting a custom WB might be desirable in some cases.
4 - Custom WB comparisons DNGs vs JPGs. I compared the daylight custom WB to the ring light custom WB and found the DNG results to be reasonably close. Comparing the JPG results varied due to the JPG processing by the camera. I would recommend shooting DNG photos for the most accurate color results.
Sorry about the length of this reply. It seems that when I start out to test one thing, I keep coming up with more things I want to test as well....
