Mastering photography lighting...How to deal with difficult reflections
How we see objects
When light hits an object, it does one of three things to the light, it let's it go through (transmission) like in air or glass, it absorbs some or most of the light, or it reflects some or most of the light. Most of the objects we see do are not transmissive, so a large part of what we actually see are reflections. In photography, we're primarily concerned with how those reflections appear in the objects we're shooting. Sometimes we want to see a reflection of the light source in the object (also called the catchlight) and sometimes we want to hide it.
When an object is lit by a light source, sometimes we can tell where the light source is by looking at the object itself. I shoot a lot of DJs, and they LOVE to wear sunglasses. They protest if I make them take them off. So one of the decisions I have to make about my photograph is wether or not I want to see the catchlights or not.
The way the source is reflected by an object is visible in one of three ways. Direct Reflection, Diffuse Reflection and Polarized Direct Reflection. The first two are very easy to tell apart, the last is a little harder, but still important to photography. It's important to note that no object is a perfect example of these different type of reflections and that most objects reflect light in one or more of these different ways.
Direct reflection, which is sometimes called specular reflection, it's pretty easy to understand. It's simply a reflection of the original light source that we can see in a photo. An example of an object producing only direct reflections is a mirror. Direct reflections follows something called the law of reflection, which says that the angle of incidence equals the angle of reflectance. That means that you will very clearly see the reflection of the light source at an angle corresponding to it's origin.
In the eye of the beholder
The interesting thing about direct reflections (reflections where the light source is visible) is that they appear in a photo (and are visible by your eyes) only as long as they are within a limited range of angles. This is called the family of angles which cause direct reflections. They are relative to the position of the light source, the position of the object and the position of the camera seeing the object. Ocasionally, you'll be photographing subjects where you'll have to manage the family of angles in such a way that you are showing, not showing the reflection or are overpowering the reflection.
An object can also affect how the light source reflects it by diffusing the light or reflecting it in different angles. Anything that looks white like a sheet of paper is a good example of diffused reflections. When you look at a sheet of paper, you'll notice that it is generally difficult to tell where the light source lighting it is coming from because white spreads the light so that it looks like it's coming from everywhere.
Because of their capability to produce direct reflections, some subjects are difficult to shoot like glass, metal or other shiny objects. So careful thought has to be given to the position of the light source in relationship to the subject. As a matter of fact, great photographers consider the family of angles a driving principle when positioning their lights.
When positioning your lights to deal with the reflections you have three options. Show the reflection partially, put the reflection outside the family of angles that cause direct reflection or make the light so big so that it covers all of the angles that cause direct reflection. There is no right way to do this, it's an artistic decision you have to make as an artist, but careful lighting involves considering the reflections and how you want them to look.
Polarized Direct Reflections
There's still that small issue with the "other" type of reflections we haven't talked about...polarized direct reflections. Some objects can absorb the wavelengths given off by light and reflect some of the light only in certain patterns. We call that polarization. Some objects like water, plastic can create a lot of polarized reflections that can be filtered out with polarizing filters. You've probably experienced something like this when you put on a pair of sunglasses. Sunglasses are built to filter out any polarized radiation.
Since certain objects polarize the light into certain angles, you can purchase a polarizing filter for your camera (or use a pair of sunglasses) to cut down the amount of light coming from those angles. Choppy water, for example, tends to polarize the light rays in a horizontal manner, so polarized sunglasses only allow light that is organized in a vertical manner, therefore cutting down the glare.
This characteristic of light gives you an added tool in photography. Some photographers polarize their light source on purpose, then can then control how some objects which give off polarized radiation look when photographed.blog comments powered by Disqus