In-camera White Balance Targets Compared

[rfcurry]

I thought it would be interesting to compare the different CCWB (Camera Custom White Balance) effects based upon the targets used when setting the CCWB. I used a Panasonic full-spectrum GF1 which permits two custom WB. Lens was Schneider Kreuznach 40mm f/4.5 Jsogon with Exakta mount. UV bandpass filter was an SEU Gen1. All photos taken in ISO 400, f11. Focus used for visible images was also used for UV images. Post processing was a single-click WB in Gimp2, then crop, and reduce to 1000px width.

 

Visible - entire image chosen as WB target

http://uvroptics.com/images/VisNWBawb1000px250.jpg

crop of above

http://uvroptics.com/images/VisNWBawbcrop250.jpg

 

PTFE target held in front of lens as WB target for UV

http://uvroptics.com/images/UVPtfeawb1000px254.jpg

 

crop of above

http://uvroptics.com/images/UVPtfeawbcrop254.jpg

 

 

UV entire image chosen as WB target

http://uvroptics.com/images/UVNwbawb1000px251.jpg

 

crop of above

http://uvroptics.com/images/UVNwbawbcrop251.jpg

[colinbm]

What do you mean by....

" UV entire image chosen as WB target "

[rfcurry]

Colin,

 

I should have used the term "WB standard" instead of "WB target".

I seldom use a PTFE white standard to set custom WB. Usually, I simply click "Set WB" on the scene itself. This usually provides more colors and variety in the UV image.

Thanks.

[Andy Perrin]

I don’t really understand why the PTFE is giving you such a poor white balance result. The images you made that way have a strong color cast to them. When I do it, my PTFE WB results look much more like the whole-scene WB results you obtained in the last two pics.

[Stefano]

Yes, that's odd. Was the PTFE overexposed?

[rfcurry]

Andy and Stefano,

 

How are you using your PTFE standards? Is the PTFE the only thing your lens "sees" when you set the WB?

Thanks.

[Stefano]

I never used PTFE, but I use a paper tissue in the same way I would with PTFE.

 

Yes, that's the only thing the camera sees. If you introduce something else, the camera will use that too to calculate the WB.

[rfcurry]

Stefano,

 

Exactly. Then, perhaps the difference we experience is a result of the algorithm used by the camera maker.

[Stefano]

It could be, but I still think the issue is that you overexpose your PTFE standard, since your camera seems to be capable of setting an appropriate UV WB. PTFE is very bright in UV, it reflects almost 100% of UV light, and most things like to absorb UV. If you correctly exposed the dirt and flowers, you likely overexposed your PTFE standard.

 

When using it to set your WB, try to go down a couple of stops, even more if necessary. This way you should be able to white balance properly.

[rfcurry]

Stefano,

 

The palm of my hand (left) is not highly UV reflective, so I don't think I overexposed it. The following were taken with the hand as the white standard. It was a cloudy day and the sun may have quickly appeared as I took this shot.

http://uvroptics.com/images/UVHandawb1000px257.jpg

 

crop

 

http://uvroptics.com/images/UVHandawbcrop257.jpg

[Andy Perrin]

My cameras (Sony NEX-7 and A7S) both take a white balance from a small circle shown on the screen in back, and they automatically stop down as far as the automatics will allow with a manual lens on there (by changing exposure time, I think). It is still possible to overexpose if it’s beyond the range the camera can automatically adjust for.

[Stefano]

Stefano,

 

The palm of my hand (left) is not highly UV reflective, so I don't think I overexposed it. The following were taken with the hand as the white standard. It was a cloudy day and the sun may have quickly appeared as I took this shot.

http://uvroptics.com/images/UVHandawb1000px257.jpg

 

crop

 

http://uvroptics.com/images/UVHandawbcrop257.jpg

Reed, are those white balanced against your hand? They look non-white balanced to me. I am missing something perhaps.

 

My Canon EOS M uses the entire image to calculate the white balance. My old point-and-shoot (Panasonic DMC-F3) used a rectangle in the middle I think.

 

From my personal experience, and seeing other images posted here, human skin is slightly lavender in UV. The tongue and lips are UV-yellow, as a curiosity fact. This means that using your hand should produce almost perfect images, a bit on the yellow side

[Andy Perrin]

Stefano, I don’t know why you think white balancing against something that’s lavender when the white balance is on PTFE would give “almost perfect images”. It is a fact that PTFE has almost constant reflectance and skin does not.

[Stefano]

I will try to be clearer. Skin is a bit lavender, not a lot but just a bit (from my experience), and so if you use it to white balance your images they should come out almost perfect (at least, reasonably good), but a bit yellow (yellow being (more or less) the complementary color of lavender). Of course PTFE is better, no doubt on that.

 

I can see the lavender color of my skin now that the lens I use has a good bandpass, on my point-and-shoot my skin was actually gray, I could have used it to white balance my photos (but I never did it).

[Andy Perrin]

My skin is a lot lavender on my good lenses. I don’t think I would advise using it for white balance under any circumstances. Outside it’s better to use asphalt. I mean amount of melanin probably influences skin color in UV dramatically. We do not all have the same skin.

[Stefano]

I agree. Also my Chinese BG39 filter is a limiting factor for me, so it is possible that skin would appear even more lavender to me using a better filter.

 

Concrete and most rocks are UV-gray, so can be used to white balance images. PTFE/Spectralon is still the best in my opinion.

[Stefano]

I mean amount of melanin probably influences skin color in UV dramatically. We do not all have the same skin.

My skin is much darker in UV, and if I get even a slight suntan on my hands the difference in UV is much more visible.

[colinbm]

Gee I just done know how you guys can argue about sub-standard WB. There is just one standard, PTFE, the rest will be used for artistic effects.

[rfcurry]

Colin,

 

Labsphere makes a number of optical standards...all of them blisteringly expensive. I sometimes use the 99%, but I also have a 20% that is handy.

 

https://www.labsphere.com/site/assets/files/2628/pb-13058rev02_standards.pdf

[colinbm]

Yes I realise that it is expensive, but Andrea & Birna would prefer botanical photos to be taken with a white balance with at least PTFE which is more cost effective.

Anything else is just for artistic effects.

[Andrea B.]

Thanks, Reed, for the interesting illustrations of WB. It's always good to see such examples.

 

 

........a few comments from loooooong experience.....

 

*An in-camera white balance is not necessarily "perfect" ESPECIALLY when working with dark filters like UV-pass or IR-pass. I have a classic example of this posted here: Strange white balance results with my GH-1?

 

 

*Even if your botanical WB was not made with PTFE or Spectralon or even if your botanical WB is not "perfect", we will take 'em anyway.

 

*I have reminded members for years now that you can white balance most UV images by putting the raw into either Daylight or Incandescent in the converter and then white-clicking around on pinkish/magenta areas to get the blue/yellow thing. We try to support low cost solutions here. This is one of them. Try experimenting with this.

 

*White balance against skin?? Whose skin?? You are likely to get a multitude of different results on that.

 

*I agree with Reed that a white balance Against the Scene usually produces a nice look for either UV or IR landscapes, cityscapes or other larger scenes. Several members here use that method. For us Nikon users whose converted cameras are a bit challenged in the white balance arena, we can achieve a similar thing in the converter using Average White Balance. If you don't have such a setting in your converter, then just drag the WB dropper around the whole frame in a random fashion.