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UltravioletPhotography

Xrite Colour Checker grey scale from 250-800nm


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As I started my journey into UV photography I wanted to find a way to calibrate my images for amount of UV being absorbed. Given I had an Xrite Colour Checker chart (one of the cardboard ones about A4 size) I thought that I would try the grey scale part of that and see what it would look like. Yes, I know these have been reported as not being good for UV, but I wanted to see just how bad they are and whether it would be any use. Obviously I know now of other approaches and proper UV calibration standards, but heh, I'm a scientist I like to experiment.

 

To understand how it was behaving in UV I cut up the chart and measured the 6 relevant tiles (white through to black) for reflection on a Perkin Elmer Lambda 650S UV-Vis spectrometer (150mm integrating sphere) between 250nm and 800nm (1s collection time per nm). The graphs are shown below, both the full range and the 300nm to 400nm portion and 400nm to 700nm portions.

post-148-0-43255300-1496733822.jpg

post-148-0-95520100-1496733827.jpg

The 6 lines are the 6 tiles along the bottom of the card, from 1 (white) through to 6 (black).

 

This to me demonstrated just how bad these are for UV. Interestingly though they weren't completely neutral in the visible spectra either, especially at shorter wavelengths and for the lighter tiles.

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Andy Perrin

1) Always worth checking things people tell you!

2) Yeah, these are terrible but they're the first actual measurements of HOW terrible they are that I've seen. (Although other members have spectroscopes and it wouldn't surprise me if someone has done this before and I just haven't seen it.)

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Jonathan, thank you for this spectral measurement of the CC neutral patches. It is always great to have the numbers to back up our various empirical observations.

 

The violet area around 400nm is always tricky as the wavelengths begin to shorten into the UV region.

 

Small question: Is your CC chart from before or after Xrite reworked the patches in November 2014? Just curious. I do not think it would make a noticeable difference in the results because obviously Xrite would continue to use visible pigments on the card. But we should try to refer to the before/after date if possible.

 

New CC specifications:

http://xritephoto.co...&SupportID=5884

 

Where to find card date:

http://xritephoto.co...D=5883&catid=28

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No problem Andrea. Not sure on the date. I'll have go back through my records and see when I bought it. Will update when I've found out.

 

EDIT - I bought mine September 2014. I guess it's an old one then....

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The Black patch was the only reliable one to use before, and now we learn why. Thanks.

 

The smaller Passport behaves in a similar fashion. The bigger chart (A4 size) is too delicate to use in the field, thus the passport is my preferred version.

 

Xriite T1402241433.jpg

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