If I could bring only one piece of equipment beside my camera, it would without doubt be my reflector. I use a reflector for all kinds of portraits – high key and low key studio portraits, and for natural light portraits indoor and outdoor. I think that I use it for 99 percent of my portraits. Reflectors come in many flavours. White, silver, gold and with stripes of each of these colors. My favorite one is the one with stripes of gold and silver. This give me a soft, slightly golden light that I find suitable for most applications.
When you use it, you usually want to light the face from below and make the light hit the face just as high as you don’t make the subject squint. This removes shadows below the chin, the nose and eyes. In addition it gives you a very attractive and sparkling reflection in the eyes that makes your subject look real and alive in a way that no studio flash ever can (and certainly not the built-in camera flash).
The best thing about reflectors is, that they aren’t that expensive. You can find professional quality reflectors with a price tag of 200 dollars, but a cheap 10 dollar reflector from eBay will pretty much reflect the light the same way as the expensive one. And you can do it with even less than that. When making spontaneous portraits at private parties and family reunions, where I didn’t bring my reflector, I have used large pieces of white cardboard, aluminum foil trays or large metal plates from the kitchen. Anything that can reflect light will work better than not using anything.