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Ah, understood. I misunderstood thinking that I only needed to shoot the greycard for the WB. With that being said, if test on an ultra wide angle, does the gray card need to be in focus? Just thinking that at 14mm or 16mm I would need a huge grey card.
And forgive my ignorance, but just for clarification when you say “shoot grey card, insert or attach nd filter...”. You mean shoot the grey card with the filter attached correct?
Thank you!
JBPhotog wrote:
There are too many variables not controlled in this method, as in minor position errors in the sampling area.
Please reread my suggestions, “only shoot a grey card” for your eye dropper sampling with the two different ND filters. Any RGB bias will give you a more accurate reading as to the shift. Your sample images induce unknown RGB values from the coloured wall.
To reiterate:
Set a custom WB in camera, only controlled lighting source as in Full Sun, no clouds, or a constant light source like a tungsten filament, not a fluorescent or LED flickering light source. Make sure the grey card is being fully illuminated.
Using that custom WB shoot your grey card, exposure #1, this is your Control. If you did everything right in the above steps, your eye dropper sampling should be R:128, G:128, B:128 or close to that based on exposure bias. The “critical” aspect is, all RGB values should be the same number.
Exposure #2: shoot grey card, insert or attach ND filter adjust shutter speed only for proper exposure as aperture value changes can influence vignetteing.
Exposure #3 shoot grey card, insert second ND filter and repeat, adjusting shutter for proper exposure.
Evaluate all three exposures in post noting your control RGB values, ND1 and ND2 RGB values will reveal any colour shift bias. Example, if your;
Control is R:128, G:128, B:128
ND1 is R:128, G:131, B:128, slight green bias
ND2 is R:128, G:128, B:135, slight blue bias
Or
ND1 is R:137, G:128, B:135, is a magenta bias
Etc etc....Show more →
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