Points in Focus Photography

Mired/Filter Calculator

Using the Calculator

To Calculate a Correction Needed to Match Lights

Use this process to either convert lights to match a film’s color temperature or to convert lights to match another light’s color temp.

  1. Enter the color of the light you are converting into the color temp 1 (source) box
  2. Enter the color temp you’re targeting in the color temp 2 (target) box
  3. Read the mired shift from the mired field.

For example, if you’re shooting with daylight balanced film (5500K) in a tungsten lit environment (3200k), you’d need to shift the light’s color temp from 3200K to 5500K. You’d put 3200K in the color temp 1 box, and 5500K in the color temp 2 box. This is a shift of -131 mireds, and would require either a 3/4 or full CTB filter.

Cooling Filters Warming Filters
1/8 CTB -18 1/8 CTO 26
1/4 CTB -35 1/4 CTO 64
1/2 CTB  -78 1/2 CTO 109
3/4 CTB -112 3/4 CTO 124
Full CTB  -137 Full CTO 159
1.5 CTB -200 Double CTO 312
Double CTB -274

To Calculate a Camera Correction Filter

  1. Enter the color temperature of the lighting in the color temp 1 (source) field
  2. Enter the color temp of the film you’re using in the color temp 2 (target) field.
  3. Read the mired shift needed for the correction in the mired field.
80A -131 85B 131
80B -112 85 112
80C -81 85C 81
80D -56 81EF 53
82C -45 81D 42
82B -32 81C 35
82A -10 81B 27
    81A 18
    81 9
Cooling Filters Warming Filters

E.g., if you have daylight balanced film (5500K), and you want to shoot with it in a tungsten interior (3200K) there’s a mired shift of -131, indicating you need a cooling filter of type 80A.



Sid Bojangles

The source/target are mixed up in the calculator and I think the comments about negative being a shift toward warmer (and vice versa) are also backwards (well, once the other part is corrected). Or the cooling/warming filters chart is wrong? Anyway, it’s all mixed up. Please correct.

    Jason Franke  | admin

    Apologies for the confusion. I was trying to do several types of conversions using only a single form without adding any additional logic to it, and I think that may have been a problem.

    Mired values are negative when the shift is towards blue/cool and positive when the shift is towards amber/warm. The filter mired values were taken from published filter values, and are correct.

    I’ve tried to clarify the language. I’ve also put this calculator on the list of potential projects to update to be more usable.



Maybe the calculator is not meant to work this way, but if you want to calculate what K value using a certain mired value will create (Color Temp 2), the result is incorrect. Basically, I’m talking about reversing the equation. For example, put 5600 as Color Temp 1, put 3200 as Color Temp 2, the mired value is correctly calculated at -134. But, now clear the fields, put 5600 as Temp 1, put -134 as mired value: the calculated Temp 2 shows as 22436.

Also, I think it is confusing that the target CCT is labeled as “Color Temp 1” as the conversion is something that has direction of “from – to”. So it is the “Color Temp 1” that should be the temperature of the source before the conversion, and resulting one/target should be the Color Temp 2.



    Jason Franke  | admin

    So it’s not confusing, it’s just broken… But I guess that’s confusing too…

    I think I fixed it, at least it seems like it’s working right for me now. If I go from 5600 to 3200 I get -134, if I go from 3200 to 5600 I get 134. If I put in 5600 for color temp 1 and -134 for the mired, I get ~3200K for color temp 2.

    I also rearranged the color temp and mired boxes and added mired conversions for the color temps directly (they appear in parens on the same line as the color temps). I think this might make it more clear what’s going on.

    In any event, you probably will have to force reload (ctrl+shift+r or cmd+shift+r) the page to get the script to update in your browser. Sorry about that.

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