A few years ago, back when film ruled, all serious photographers learnt about warming filters and why they are useful. The filters come in serveral strengths, but the most common are 81A, 81B and 81C (in increasing power). In a classic case you might find yourself taking photos in a shady area using Ektachrome under a sunny blue sky. Once your film was developed you would find that everything had a blue cast due to the light quality. The light under these conditions might be measured at 7000K or higher, very blue. By adding a warming filter you could bring the light hitting the film back down to a lower kelvin level (“warmer”) and eliminate the blue cast. Adding a warming filter when taking photos of people generally made their complexion better, especially if you were using any type of strobe, since these are usually balanced to 5500K. The idea was to warm up the image by enhancing the red and yelow end of the spectrum, producing warmer colours. In the digital age however, warming filters are no longer necessary. There are various ways to approach this, one is to do some post-processing with Photoshop using the built in photographic filters that are available, or to play with the RAW white balance settings, but this extra work takes time. Instead it is easier to ust have your dSLR do the work. There are various ways to mimic the action of a warming filter in most dSLRs, i) is to set the white balance manually to something like 4800K; another method is to use the built-in white balance options such as cloudy or shade which will alter the white balance to a lower Kelvin temperature; in some cameras such as my D200 you can adjust the auto white balance to -2 or -3 which has a similar effect to the other approaches I have mentioned.

On a recent trip I did some side-by-side comparisons to see what effect the camera controls would have a particular scene. In this case we had high bright clouds with no sun. The conditions made for rather cool light in the area I was especially since I was working in an area with lots of black and grey coloured rocks. below you can get an idea of how the camera settings can affect the resulting image. The following are in no way exhaustive, but they give a god idea of what you camera can do by changing a few settings.

The first image shows the auto White Balance jpg. Giving a rather grey and cold image.	The next image is slightly warmer with white balance set manually to 4800K. This looks a little better.
The next image was created with the white balance manually set to 4500.	The final image was created with white balance set to shade.