One of the best ways to achieve a nice soft light on your subjects is to use a scrim. These scrims can range from large reflectors to giant sheets, but they all perform the same task, and that’s diffusing hard light. The problem with scrims is that while diffusing the light, they also lower the power of that light. This loss in power is dependent on the specific scrim you are using and can range from a quarter stop of light all the way to one and a quarter stop of light. The problem with this is that as you lower the light on your subject, while still getting a proper exposure on them, you are in turn raising the exposure of your background. In this video you can see how Joel Grimes uses a scrim net to help control this added brightness to his background.
When lighting a subject, it’s common for a photographer to want to have the background slightly darker than the light on his subject. When using a scrim as a light diffuser, this is an inherently hard task to complete. In the example from the video, Grimes is using a one stop silk to diffuse the light on his subject. While keeping a correct exposure on his subject, this makes the background one stop brighter.
In order to combat this effect, Grimes adds a two stop scrim net behind his subject. Now with minus one stop on his subject and minus 2 stops on his background, the background now has an effective minus one stop when maintaining a correct exposure on the subject.
As mentioned in the video, the main issue when using this technique is the possibility of the net showing up in your image. By using a shallow depth of field, any detail in the net is blurred away and unnoticeable.