Sunday, June 5, 2011

[UV] on whitebalance tolerance using a GH1-UVIR

In previous posts on whitebalancing using my ReflectionDisc I warned about generalizing results and stated that it is only valid for that camera, that lens, that filter and that lighting situation. Well, I was curious, how much would change if two parameters were changed: a) lens in use, b) lighting situation

So, using my GH1-UVIR, a Cerco 94mm lens, Baader-U filter and sunlight, I had preset a whitebalance for that situation using my Reflection Disc, call that WB1 for now.

The weather today was different, quite well lit, but overcast and no sun. A set WB was done, call that WB2.
Also the lens was changed, form a color corrected, flat transmitting (<300nm) quartz / fluorite lens to a non-color corrected suitably UV transmitting conventional enlarger lens, which reaches about 350nm, to see which impact that would have. So what we see here is:
1) top left: Cerco 94mm lens, correct WB for that lighting situation set (WB2)
2) top right: Cerco 94mm lens, previously set sunlight WB used (WB1)
3) bottom left: 95mm enlarger lens, correct WB for that lighting situation set (WB2)
4) bottom right: 95mm enlarger lens, previously set sunlight WB used (WB1)
[click on image to see a larger one]

Interesting to note, that only the blue and red channels are shifted just a bit, which can easily be corrected afterwards in post processing, but the image out of the camera is still quite close to the "correct" one.

That's important if you're out in the field and the lighting situation changes and / or different lenses are used (as long as they are suitably UV transmitting; this may not work for white angle lenses having hardly any UV transmission). For critical scientific work I would of course always do proper whitebalancing upfront.

SUMMARY: UV whitebalance, once correctly set, works suitably well also under changed situations (light, lens)

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site