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UltravioletPhotography

Using the Color Checker Passport to White Balance a UV Photo: the Black Patch Works


Andrea B.

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Guess which patch on a CC card might be useable for white-balancing a UV photograph?

The black one !!!

 

Somewhere in the dusty corners of my mind, I think I knew this but had forgotten all about it. So I decided to put up a post for future reference. :D

 

Set-Up

Here's my CC Passport together with some Labsphere Reflective Standards which have 99, 75 and 50% reflectivity across IR, Visible and UV. The rightmost 6 CC patches in the photo are the Visible neutral squares which vary from white at the bottom, through grey to black at the top. (There are some neutral squares on the other page too, but I've covered part of them with the Standards.)

D600_Vis_Sun_070613wf_12928origProofPn.jpg

 

 

Procedure

I made a UV foto of this setup using the D600-broadband + UV-Nikkor + Baader-U UV-Pass filter.

Then I brought the foto into Capture NX2

and used the white balance tool on each of the six neutral patches in succession.

Develop > Camera Settings > White Balance > Set Gray Point > Marqee Sample > Start

 

White Balance on the CC Passport White & Grey Patches:  Not Good

The first 5 patches do not give a well-balanced result - a yellow cast is produced.

D600_UVBaaderU_Sun_070613wf_12932wbOnPatch1.jpg

D600_UVBaaderU_Sun_070613wf_12932wbOnPatch2.jpg

D600_UVBaaderU_Sun_070613wf_12932wbOnPatch3.jpg

D600_UVBaaderU_Sun_070613wf_12932wbOnPatch4.jpg

D600_UVBaaderU_Sun_070613wf_12932wbOnPatch5.jpg

 

 

 

White Balance on CCPassport Black Square:  Not Bad

This WB result might be the tiniest bit more blue than the next foto, but it is probably close enough for all practical purposes. "-) 

You can investigate whether it works with your UV kit and your editors. (Remember, under- and over-exposure can affect the outcome of the white balance step.)

D600_UVBaaderU_Sun_070613wf_12932wbOnPatch6.jpg

 

WB on Labsphere 99% White Standard

D600_UVBaaderU_Sun_070613wf_12932wbOnWhiteStd.jpg

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