One of the most frequent questions I get asked when it comes to underwater macro photography is how to achieve black backgrounds. The popping colors of the subject on black creates great contrasts in an image.
Generally speaking, a black or dark background is achieved by a small aperture. You would want to let as little light as possible through your camera lens. However, it’s not just that easy since a big F-stop/ small aperture automatically means greater depth of field!
Therefore, there is situations where it’s close to impossible to achieve black backgrounds and make the colors pop. For instance, when you have reefs or sand behind your subject and you cannot get any lower with your camera. In that case, you’re better off choosing a small F-stop/ big aperture, aiming for a shallow depth of field in order to separate the foreground from the background.
Here’s a perfect example why it is so important to “go low”: this Blue-Ringed Octopus stayed stationary on a piece of rock, and in perfect position for a black background shot. First image has been taken slightly from above, with a small aperture of F22, even the sand in the background is still in focus. Next photo is taken from even lower, keeping the exact same settings but now getting a clean, black background.
Another way to achieve black background, depending a bit on the subject and situation, is to use only one strobe so that the subject creates a shadow behind itself. Perfect example is this Warty Frogfish. Whereas I used two strobes for the first shot, filling in what is behind the Froggie, I switched my right strobe off for the second image. Only the left side and face of the subject got illuminated keeping the background in the shadows and therefore black.
A very common but slightly more difficult technique is using a snoot to create only a spotlight around the subject and keep the rest of the image dark and black. I will not go into detail about the snooting technique, if you’re interesting in finding out more, here’s another blog post I’ve created a while back. See the huge difference between the first image, taken without the snoot (F6.3) and the second photo, using a fiber optic snoot at F11.
This leads me to a general recommendation when trying to create different colored backgrounds. As discussed earlier on, small apertures and big F-stops create greater depth of field and darker background. Whereas big apertures and small F-stops will help you if you’re aiming for a nice, blue background.
Check out the first photo of a Whip Coral Goby, taken at F6 which makes for a completely different picture compared to the second one taken at F22 – just to show you the two extremes. Same goes for the Juvenile Cryptic Sponge Shrimp, first shot at F22, second one at F7.1
Last but not least, there’s always the option for a night dive and guaranteed “black” behind your subjects 😉