How to Create Portraits with a Black Background
Who does not love a crisp, deep black background for a portrait. You can achieve this with the application of just two ideas, and just a little post-processing too.
We are talking about a couple of techy things in hopefully, a non-techy way. These two ideas will give you tips for how to make black backgrounds for your portraits.
No calculations necessary
As an erstwhile teacher of Mathematics, I should not apologise for numbers, There is quite a lot of Mathematics in photography. However, you may be pleased to know that I think you can achieve everything, without thinking much beyond the basics. If you have a broad understanding of the concepts you will be absolutely fine.
These techniques are not just applicable to portraits.
Firstly, please think of stops of light as units. Using the term stop is like saying that something weighs 12 kilograms or that it is 10 miles away. As photographers, we tend to talk about stops and stopping down, but it is just as valid to say units. The thing is not to get bogged down in technicalities, the term stop is only a unit of measure.
The falling off of the light
The first concept might be stated simply as light falls off rapidly. Fleshing that out just a little, the amount of light available decreases greatly as you move away from the source of the light. But we are photographers and we do tend to think that a picture is worth a thousand words. One unit of light arrives at our subject, one meter away from the window. If she moves two meters away, just one-quarter of a unit of light will now be arriving at her. Then, if she moves three meters away from the window, which is the source of light, there will be only one-ninth of a unit of light. The available light disappears very quickly.
How does that affect the background
When trying to achieve a black background, you are interested in the amount of light hitting it. Again, pictures tell the story best. Both these photos had only white balance and very small adjustments to balance exposure done in post-processing.
The image on the left has the background close to the subject, about three feet (one meter) behind her. Then, on the right, the white background is about thirteen feet (four meters) back. You do not need me to do calculations, quote some nice formulae, to prove what is happening above.
In these photographs, the subject hasn’t moved and the exposure does not change. The background moves farther away, and the amount of light reaching it reduces rapidly. Even when the background is white, rather than the desired black, it gets much darker the greater the distance it is positioned from the light source.
In the practical world, there may be limits to what you can do, perhaps by the shooting space you have available. However, the message is simple, push the background as far away as possible, and even a seemingly small distance will help make it appear darker.