Color Temperature Blues - What Are Color Correction Filters?

Posted: 05/21/2017

Blog by Leslie Lazenby

How are feeling today? Do you know your color temperature? Not knowing can give you the blues or even a fever.

I've always thought color temperature is hard to explain. Here is a truncated definition from Wikipedia: "Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture, and other fields." Here's my version, "Every (white) light source gives off a certain color, our eyes can't see the difference unless the souce color is extreme or we have side by side comparisons."

Here's an example, if I have on a white shirt and ask you what color it is and it's lit by these different light sources; outside at 12 noon, outside at 8 p.m., inside lit by flash or studio strobe, fluorescent light, tungsten light or by led light, you would say, "white White WHITE!" Yes to our eyes, but to film, NO. How would these situations record on a regular roll of film, say Kodak Gold 200. outside at 12 noon - white, outside at 8 pm - yellowish, lit by flash or studio strobe - white to cool white, fluorescent light - greenish, tungsten - yellow or reddish, and led light - cool white. Not at all what your eyes and brain registered.

We need a way to predict how our subjects are going to record on film. With a little knowledge you can control how  accurately color renders to film and use color shifts to enhance the mood of your images. You have two choices predicting your results, experience, knowing your basics and/or buy a color meter. The color that lights give off is given as a rating, a name, we call the rating for color temperature Kelvin.  As an example a reading of 5500 could be called 5500 degrees Kelvin or simply 5500 Kelvin and written as 5500K. When you know the Kelvin rating of your light source you can predict how your daylight film is going to record your image. Daylight 12 noon sun is rated at about 5500 to 6500, this is considered the norm where all other sources are compared. Lower ratings or readings below 6000 K are considered warmer,  the lower the number the more yellow to red it will record on film. Numbers or readings higher are cooler or bluer.

How do you control it now that you what it is? You have a couple of choices, correctly balanced film or a filter over your lens  when you do not have the correct film for the light source. Consumer films are either balanced for daylight or tungsten lighting. Most films are daylight balanced, even if it is not specifically stated. Films balanced to give you correct color with tungsten lights with usually have a "T" in their names, such as Ektachrome 64T. Film families like Eastman Kodak's Vision 3 offer both, and are appropriately named 50D, 250D, 200T and 500T.  There is no guessing the speed or the light source this film is balanced for.

35mm SLR Camera with a color correction #85 filter over the lens.

Placing a filter over your lens corrects the color when you want to use a film not balanced to your light source. The 85 family includes 85, 85A, 85B and 85C are orangish in color and are used to balance a tungsten film to daylight light source.  If I have that wonderful Vision 3 500T in my camera and want to shoot in daylight I use an 85 series filter over my lens and the color is perfect. You may have noticed there are A, B, C versions of these. There are roughly 200 K difference between each one of these, it really fine tunes the correction. 85 is the strongest then a little less with A and even less with B, etc. Today most of our images are going to be scanned and 200 Kelvin is so small it is only a slight correction in post. Digitally correcting 200 K  verses a 2000 K  correction is a lot easier for a successfully color balanced image.

Filters and Filter Factors

There are filters made for nearly every situation, use the 80 family to correct daylight film to tungsten light. Even fluorescent light can be corrected, FLd corrects for fluorescent, to daylight and FLb corrects for fluorescent to tungsten. Filters absorb some of your light. If you meter though your lens with the filter on there is no exposure correction needed. If you sunny 16 or use a hand held meter you need to know the filter factor and correct for it. This is a good reason to keep one of those little multi folded sheets that come packed with the filters handy, they tell you how much to add. If you are using a hand held meter you can hold the filter over the sensor for a corrected reading.

I did not address the color meter for practical reasons. They are costly and can drive you a bit buggy if you fixate on every little color shift. They operate like a light meter, read the light illuminating your subject and it gives you the Kelvin reading. In our Photoshop era these small color shifts are corrected with a click of the mouse. Some still have a need for them but not like years past. Remember the closer you get to correct color the less time you will spend behind the computer monitor correcting it out. Also knowing how color shifts during the day can give you a lovely dreamy warmth by just shooting earlier or later in the day. Use your color temperature knowledge to your advantage to avoid surprises and then you won't have to sing the Mean Old World Color Temperature Blues.
Mean Old World / T. Bone Walker:


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