To Flash or not to Flash...Is that a Question?

Of all the topics in my beginning and intermediate classes, flash photography is the least understood.  In light of that I thought that a discussion on flash and some information on how light behaves might be on target.

I suspect that I might be able to illuminate you with several posts on this topic.  Lets start with some information on how light works.  After getting a handle on a few basic characteristics of light, we will move the discussion toward using a flash to take some pictures.

Lets start by talking about three key characteristics of light:

1. Light diminishes at a known rate as it moves from its source.
2. Light and earthquakes have something in common
3. The "character" of light changes based on the size of the source and its distance from the object it falls on.

OK, all you right brainers, don't run away, I am one of you and I promise to keep this pretty intuitive and as general as possible!

So...light diminishes at a known rate.  Simply stated, as light moves from its source it spreads out and as it spreads it loses intensity.  Think of getting blasted with a water hose.  If you are 3 feet away the hose will hit powerfully and all the water will hit you in a small circle.  If you are 20 feet away you will be hit with a gentle spray of water that covers your entire body and a lot of area around you.  It is the same amount of water, it just spreads out over distance.

Light works the same way and it does it at a known rate so we can easily visualize how it works.  It's called the Inverse Square Law.  What it says is that every time the distance from the source to the subject doubles, the light will be 1/4th as intense.  In other words it will lose two stops, one stop is half, two stops is half again or 1/4th.  Got it?  If not, take a close look at this illustration:

For example: If I take a picture of you and you are 10 feet from the camera and there is a wall behind you that is 20 feet from the camera, the light on the wall will be two stops darker than the light on you.

One word of caution, there is a BIG variable out there that can mess with your results and that is ambient light (the light that already exists on the scene).  In very bright situations your flash is too weak to overpower the existing light so the Inverse Square Law will appear to break down.  The Inverse Square Law works best for visualization of lighting when you are working in lower light situations were the flash can overpower the ambient light.

You will use this information to visualize results when you use your flash in people photography and in nature photography.  It is most helpful to me when I use flash in closeup photography.  I also used this visualization technique frequently when I was doing professional portrait work.  Much more about this later.

Enough for now!  We can talk about light and earthquakes in the next post.....Later