Jul 03, 2021
3 mins read
I keep seeing people asking how to control hot spots and getting suggestions to "feather the light." I know these are well-intentioned suggestions, but feathering is not the solution for controlling bright specular reflections or hot spots such as on the lips, the tip of the nose, or on shiny products.
Feathering the light
Let's first look at what feathering is and does. Feathering the light means that instead of pointing the light directly at the subject you turn it slightly away, usually across the subject and more towards the camera. Feathering lets you control where the edge of the light is so you can emphasize or de-emphasize part of the scene. It can help even the coverage of light across the face of a portrait subject. But feathering makes the light smaller (compare the sizes of the two blue arrows) width/size which makes the light harder. Look at the shadow of the nose at point D in the examples further down the page. The shadow has a more distinct (harder) edge in the feathered photo. So let's get that out of the way–feathering does not make the light softer.
But we're talking about bright specular reflections here. A specular highlight is a direct reflection of the light source and as such is the same brightness as the light source. Think of a mirror–a light reflected in a mirror is as bright as looking at the light directly. Feathering doesn't make the light dimmer. The highlights (A, B, and C in the examples below) are the same brightness with the light straight on or feathered.
Controlling the specular reflections
So, how do you control the brightness of these reflections? By light to subject distance.
The closer the light is to the subject the dimmer the highlights will be. Yes, you read that right. Bringing the light in closer knocks down the highlights. You can watch a video about this at the bottom of this post for a detailed explanation. In short, though, when you bring the light in closer the direct reflections remain the same brightness as they were at a distance, but they are larger, helping to make them less noticeable.
But the bigger change is that by bringing the light in closer the diffuse reflections (the skin, clothing, and other parts) got brighter (inverse square law). To compensate and bring the exposure back in line you need to either stop down the lens (which also changes depth of field, so you might not want to do that), shorten the shutter speed (which only works with continuous light, not flash/strobe), or lower the power of the light (usually most effective). So, if you cut the light to subject distance in half you need to lower the power of the light by 2 stops. Now the light source is four times less bright as it was at the original distance. And as the direct reflection is the same brightness as the light source, the highlights are now four times dimmer.
Bringing the light in closer has other effects. The light source becomes larger as seen by the subject, so the light is softer. That is the transition from highlight to shadow has a wider gradation. And the light is less aggressive, giving a quicker fall-off. You get nice shading across the face and the background gets darker, helping the subject stand out or allowing you to light the background separately.
Looking back at the example photos take note of these targets in the top row:
A The highlight on the bottle is the same brightness with the light straight on or feathered
B The highlights on the tip of the nose and the lips are the same straight or feathered
C The reflection of the softbox in the mirror is the same brightness straight or feathered blowing out the muntins* or sash bars
D Feathering the light makes for a harder left to right shadow transition (up and down remains the same as the tall dimension of the light didn't change)
Then compare the top row to the bottom row.
A The highlight on the bottle is dimmer and larger and less noticeable
B The nose and lip reflections are dimmer and larger and the background is darker
C The reflection of the softbox in the mirror is much less bright (you can make out the muntins*/sash bars)
*Muntin - a bar or rigid supporting strip between adjacent panes of glass
https://youtu.be/rBQG-l5EGxg?rel=0 (skip the first 20 seconds)
Thanks for following along!