This has nothing to do with shoe inserts for your feet, but rather using gels on your lights to balance different light sources, add effects, and overall improve the quality of your light. Gels are an inexpensive, yet very important tool in our lighting toolbox, and today I’ll explain why.
There are many different light sources to factor in when we are using flashes or strobes. There’s daylight, florescent light, incandescent light, sunlight… you get the idea. Different types of light have different color temperatures, and that can really play havoc with your lighting when you are shooting in an environment with mixed lighting sources.
Florescent light, for example, is not actually white as it appears. It’s actually green. Don’t believe me? Shoot some pictures in only florescent light and see the green color cast that appears in your images. The camera sees light as it really is, and even as good as the Auto White Balance feature has gotten, it still doesn’t nail it. That’s why pros use preset white balance settings or use a custom white balance.
Now, imagine if you mixed flash with florescent light. You would get white light from your flash and green ambient light from the florescent bulbs, which is going to make your subject look like crap. Not what we’re after. To remedy this, you can use a piece of green gel on your flash and set your camera’s white balance setting to “Florescent” and the light will look natural.
The same thing happens with incandescent light bulbs and flash. Your subject will have a bluish tint from the flash and the background will be exceptionally warm and orange. In this case you can use a Color Temperature Orange (CTO) gel on your flash and set your camera’s white balance to “Tungsten” and your light will look natural. Problem solved.
In the picture above and below, I shot my son and daughter at the beach just before sunset. Sunlight at that time is nice and warm, so I threw a 1/2 cut of CTO on my flash so that it would match the sunlight. This way the photo appears to be lit naturally instead of with flash. I had an SB800 on a stand firing at 1/2 power through a shoot-through umbrella, to camera right (my left). The sun was camera left and behind my subject, providing a nice rim light. The sun was dipping into the clouds which softened it up and made it a lot more flattering.