Black Background For Portraits
Black Background 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 apologize for numbers, should I? 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, so look at the diagram below:
In the example above, 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.
It might suit some if I illustrate the same point with a graph (which, in the past, I have tended to introduce to students as a Mathematical picture).
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. It is obvious, isn’t it?
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.
The black background for this photograph was the inside of a room. The teenage Filipino boy was standing in a doorway, getting the full benefit from the light source. The background, the far wall of the room, might be only eight feet (just over two meters) away, but it is getting very close to the blackest of blacks, isn’t it?
Combine this reasonably straightforward science, the way light falls away, with the science of the dynamic range of camera sensors and you will be a long way towards achieving black backgrounds for your portraits.
Please understand that the numbers I am using here are approximate. They do vary from camera to camera, and from the conclusion given by one source to another. But I am going for using what is easy, what is really needed to make the point so you understand.
Dynamic range is the measurement from the darkest to the lightest item which can be seen. Your camera has a great deal less dynamic range than the human eye. It is much less capable of seeing into dark and light areas at the same time. That is why, when your camera produces an image with blown-out highlights, and blocked up shadows. But your eye can still see the detail of a bird, which sat in bright sunlight, and you can also see the black dog which sat in the darkest shadows. Your camera simply cannot see both at the same time.
Light the subject, not the black background
It might be stating the obvious, but it needs to be said – the first step to getting a black background is to use a black backdrop. Then, if you can get the subject lit more brightly than the background, that will push the background into the underexposed, dark areas, outside the camera’s more limited dynamic range.
If you can throw some extra light onto the subject and have them exposed correctly, in the brighter end of the dynamic range, that will help to send the rest of the image into darkness. The brightly lit subject should be properly exposed. Then there is a good chance that the background will be outside of the part of the dynamic range for which you are exposing. It will, at the very least, be heading towards black.