Converter

Usage

I created this because my Lee Big stopper, like most high-density ND filters isn’t quite neutral, but has a predictable color shift so it can be compensated for easily if you know the correct color temperature for a given scene. The technique has two parts. First you must build a “profile” of your filter’s behavior, then you must shoot reference images when making your actual exposures to manually convert.

This is nowhere near as automated as I would like it to be, but it’s better than manually doing the math every time.

Profiling your Filter

The first step is to build a “profile” of your ND filter’s behavior in terms of temperature and tint shifts. I find the best way to do this is to make a number of image pairs, one with the ND filter and one without, of something you can easily white balance against. Note the temperature and tint values for each of the images in the pair.

You’ll need to plug the temperature values into my calculator to get the shift in mireds or do the calculation yourself using mireds = (10^6 / colorTemp1) - (10^6 / colorTemp2). The tint conversion is simply the difference between the two numbers.

Shooting and Using the Calculator

When shooting it’s still necessary to make a reference exposure without the ND filter. This will provide you with a reference white balance to start with. Ideally you want to shoot something that makes white balancing easy, like a gray or white card; though auto white balance will normally work as well.

To calculate the white balance settings for Lightroom/Adobe Camera RAW:

1. Set the Color Temp and Tint in from the reference image in Scene Reference section in the box at the top of the page
2. Set your filter profile values (LB and CC) in mireds and green/magenta tint in the second section.
3. Set Lightroom’s Temp and Tint sliders to the values show in the last two boxes.

Note: Color boxes will appear next to the filter reference values. They should match the color the filter image changed, i.e. if your image was bluer then you should see a blue box for temp.