Its diffuser season here in Vermont, the time of the year when there is lots of little stuff to photograph and often lots of bright sun in the sky. Unfortunately, those two things don’t usually go hand in hand. Here is my rule of thumb on the relationship between the type of light and subject- soft, delicate subjects need soft, delicate light and hard, sharp subjects need hard, sharp light. So if you are photographing wildflowers or fiddle heads wait for soft light and if you are photographing cacti and granite wait for direct sunlight.
But what happens when you can’t (or don’t want to) wait for the appropriate light? In steps the diffuser. We all know what a diffuser is, yes? A diffuser is a thin piece of white nylon in a thin flexible frame, usually round in shape that is used to soften, or diffuse direct sunlight. I call it a cloud in a bag. All you have to do is put the diffuser between the sun and your subject and viola, you’re good to go!
Ah, but there is a catch. Isn’t there always? Now pay attention, this is the important part- I think diffusers are the most misused piece of photography gear. That’s right, misused. How could you possibly misuse a diffuser? It would be like misusing a lamp shade- light bulb, sofa, lampshade goes in between the two. Sunlight, flower, diffuser goes in between the two. How is this difficult? Glad you asked!
The important thing about using a diffuser is where you place it relative to your subject. Where photographers always go wrong when using a diffuser is that they always place it too far away from the subject. For a diffuser to be most effective it has to be as close as is possible to the subject. How close is close? Here is the rule: the diffuser should be just on the outside edge of your viewfinder. When it is this close it produces a beautiful soft, radiant light that makes your subject glow. If you move the diffuser just a foot farther away the light produced by the diffuser is no different than the light produced by your shadow.
How can this be true, you ask? If you remember from your high school physics class, light diminishes at the square of the distance traveled. So it doesn’t take much
distance for the light to go from glowing to simply glum. I know, you don’t believe me. You think this is just more hot air in the hot air filled blogosphere. Okay, test it yourself. Go out on a sunny day with your diffuser and watch your subject as you slowly move the diffuser closer. The quality of light doesn’t change much until the diffuser gets almost on top of the subject. Then, as if by magic, you will see your subject actually glow. Move the diffuser back a few inches and the glow disappears. Move it back in and the glow returns. Not magic but certainly magical.
Well, that’s it, right? Nope, there’s more! This is graduate level diffuser knowledge.
Most of the time I am using a diffuser the sky is partly cloudy, partly sunny so my choices are diffused light from a cloud or from my diffuser or straight sunny light. But there is a difference between light coming through a cloud and light coming through a diffuser. Sunlight coming through a cloud is very cool, very blue whereas sunlight coming through a diffuser is very warm, very golden. So depending on your subject it may be appropriate to not use a diffuser and wait for a cloud for cool light or it may be better to use a diffuser because you want warm light on your subject.
So there you have it, everything you wanted to know about using a diffuser and then some. It is not just use it or not, it’s how you use it. Isn’t that always the way it is?