Another Lighting Question

[TonyW]

Thought I'd start a new thread rather than confuse the studio lights one. I'm confused about colour temperature of lights. Was doing some very simple experiments with a 150W tungsten flood and a 42W (150W equivalent) Daylight fluorescent (a Philips CFL claimed to be 6500°K) - both cheap household type bulbs from the hardware store. Not a fancy set-up - just put them in a desk lamp and shot a couple of pics at the same exposure. Shot RAW and the images are with my usual RAW adjustments but didn't change the colour temperature. The D80 was on Auto white balance (colour temperature) and I've found it does a much better job with tungsten that other cameras I've owned.

The RAW editor reported 3600°K for the tungsten and 5900°K for the fluorescent. I sort of expected the tungsten would give a warmer image and maybe it is in places but not consistently. I think the fluorescent looks slightly closer to the real colours if there is such a thing but they are pretty close and I guess "real colour" depends on the light you view it with.

Excuse the picture - it's not an ad but the book was handy and had the right colours including some shades of green that I wanted to see how well I could reproduce (and they do look pretty close on my monitor) :)

http://www.pixentral.com/hosted/1fezqwfuRDh88Cs8B0BI4Hq4GJnsdl_thumb.jpg (http://www.pixentral.com/show.php?picture=1fezqwfuRDh88Cs8B0BI4Hq4GJnsdl)

So what would be the best for still life shots indoors? Reason I'm experimenting is that I got volunteered into running a session on still life at the local camera club in a couple of weeks with a group who tend to just pop up their on-board flashes and fire away. Wanted to demonstrate that you can do a much better job with a cheap lighting setup up that you can get from any hardware store.

Any advice, links to articles etc would be much appreciated as I am having a hard time finding any suitable ones.

Tony

[GaryK]

Hi Tony

This link ..posted a while ago, may have some info. At the very least it looks like it may link to other sites.

http://thehowzone.com/how/Photo-Softbox/1

[TonyW]

Gary: Thanks for that. I think I'm getting it figured out. The factor I was missing was CRI (Color Rendering Index) which is as important as Color Temperature. Gets a bit technical but basically the light needs to have the color you want to see in it or you won't see it - and fluorescents can have spiky color output so some colors can be missing. I now have a collection of fluorescents with varying CRI's and color temperatures (had most of them but they aren't labelled, at least in Canada, so had to dig around to get the info). Is making me appreciate how good the sun is though - just wish we could get more of it up here this winter :D

Tony

[GaryK]

Tony

I did some colour theory years ago and you are right .. we see the colour that is reflected off of an object, so if that colour is not in the light then we won't see it.

[lexcell]

If truly accurate white balance is what you are after, you could use an Expo Disc or WhiBal card to set a custom white balance under the lights you are going to be using.
Otherwise, dropping a black and/or white point in the image will remove the color cast. You can then batch process all the images to match.
I prefer getting it right in the camera rather than having to process alot of images in post.