For my fine feathered friends!
Back again to help clarify studio lighting terms. This time I am taking on the concept of feathering. Feathering is pointing the light ahead of your subject instead of straight on to your subject. Feathering usually produces a nicer looking image. People often say a "softer" light on the image, but that isn't quite correct. Remember that the quality or character of light is determined by the size of the light in relation to the subject. You see this in the shadow edge transition. The larger the light source is the smoother the diffuse highlight to shadow transition is and the softer the light is.
Let's take a look at what happens when you feather the light. Here are photos of a 2x2-foot softbox straight on and the same softbox feathered off to one side. What do you notice first? I hope you see that the feathered light is SMALLER than the direct light. So, if the light remains the same distance from the subject, it is potentially slightly harder when feathered. But at the same time, it spreads out more across the face of your subject, giving a more pleasing look.
Working with a softer (larger) light source it isn't so easy to see what is happening. Let's start with a harder light. This time a 7-inch standard metal dish reflector.
Take a look at the 3 points labeled in the photo. A (the nose), B (the lower lip), and C (the ear). A is the same brightness direct and feathered. Why? Because it is a specular reflection and is the same brightness as the light source, no matter the distance. If the light was moved in closer the brightness would stay the same but the reflection would get bigger. If the light source was moved back the brightness would again be the same, but the reflection would get smaller. The feathering doesn't have much of an effect here.
B is somewhat similar with the small hard light source. Basically the same straight on or feathered. At point C we can see that pointing the light more in front of and across the subject a little bit of light catches the ear. I would probably retouch out that little highlight on the ear.
Go back to point A and the nose. This time look on the shadow side of the nose. The edge of the main dark shadow is about the same. With the feathered light the shadow is not as dense, but the edge transition line is pretty much the same. The feathering lowered the contrast, but didn't make a softer transition. It didn't soften the light.
Now let's work with a softer light. This time a 2x2-foot softbox.
The differences are more subtle, but they are there. Look at the same three points as before. The brightness of the specular highlight on the tip of the nose is the same brightness straight on and feathered. But this time there is a difference in point B on the lower lip. Feathering the light changed the shape of the wide highlight on the lip, but the brightness is still the same. The larger light also allowed more light to reach the ear than with the 7-inch dish above.
Again, I invite you to look at the shadow side of the nose. There is very little difference in the shadow edge transition. Feathering did not make it softer.
Comparison sliders drag to the left to see the feathered light, drag to the right to see the direct light
Hard vs Soft
Below are the feathered light images with the small and the larger light sources
Look at the same points again. A is pretty close in brightness, but the shadow edge on the shadow side of the nose is very different. That comes from the difference in the size of the light sources, not from the feathering. The larger light makes for a nicer looking highlight on the lower lip (B). If I had move the softbox back further away from the face it would have been smaller and brighter. Brighter because the rest of the face would have received less light and I would have to have compensated by turning up the power of the light (strobe) or used a longer shutter speed (constant light, which is what I used for these demonstrations). As noted above the specular highlight remains the same brightness, but I would have had to brighten up the entire image, including the specular highlight to maintain proper exposure on the face. I know that this can be confusing. So let's look at another illustration.
Again I am using a constant light, so I am controlling my exposure via my shutter speed. If I was using flash here I would vary the power of the flash to maintain the same exposure on the subject of the photo. With the light 40-inches from the can the highlight is thin and bright--too bright to read the text on the label. As the light is brought in closer a couple of things happen. 1. The highlight gets wider because the light is closer and therefore larger in relation to the subject. 2. I have to lower the overall exposure so the diffuse reflection of the can is properly exposed. This brings down both the overall exposure and the specular highlight brightness, bringing them closer in line with each other. In the third image the light is very close and its reflection is even less noticeable because it is spread out over a larger area and the brightness of the rest of the can has been brought up closer to the brightness of the highlight (and then the overall exposure was lowered to bring it all back to give the proper exposure of the overall subject). I know this can sound counter-intutive. Bringing the light in closer reduces the mirror-like specular reflections.
We see the Inverse Square Law doing its thing here. As the light is moved closer to the subject it falls off faster and the background gets darker. As the light is moved in closer the specular highlight remains the same brightness, but gets larger. As the light is moved in closer the overall diffuse reflection exposure gets brighter and we have to lower the intensity of the light.
Feathering your light can change the size and shape of specular highlights, but the brightness will stay the same. Feathering your light will help even out the exposure across your subject, but won't have much effect on the shadow edge transition (softness). Feathering your light is the right thing to do. If you want to tone down a hotspot you need to move your lights in closer. But that also affects the depth and spread of the light. So many tradeoffs in photography. More details about the tradeoffs are in my book, Anatomy of a Studio Portrait.
Thanks again for stopping by!