The first hurdle of night diving is to actually do it. Getting a beer at the bar and calling it a day is often more tempting than jumping into the water again. But once in, there is almost always one encounter or one shot that makes forgoing that beer worth it. For the best results, here are some important considerations to take with you.
The first and most important thing to bring is a torch. One for you and one for your camera. It’s equally important to be able to focus underwater at night as well as to communicate with your dive buddy or the boat that is going to pick you up afterwards. Underwater photographers often think that they have enough lights as they have their focus light or pilot lights built into the strobes. But when the focus light is on throughout the dive and the strobes have emptied out by the end, you face the risk of not having any light at the surface, which can be a serious safety hazard. It’s always better to bring a second, handy dive torch with you as a backup.
Regarding the focus light, wide and soft light will do the job well. Ideally, it should not be too strong or dimmable to low power to avoid scaring the animals away with the light. If you have the option of using a red light, it could be very useful for animals that are easily scared, but take note that the landscape will be set to a monochrome scene and it makes finding animals more difficult compared to using white light.
To start off, I would recommend using a macro lens with the focus light on top of the camera. The technicalities are similar to what one would apply during the day, though the environment has obviously changed: Animals are more difficult to spot and their behaviour is different. But this can be an opportunity to capture animals in situations that can’t be seen during the day, like a sleeping parrotfish or a hunting lionfish. At night, settings such as aperture and shutter speed are about the same as in the day. To avoid any light interference from the focus light, or from another diver, it is best to set the shutter speed to at least 1/200s. Make sure that there is no disturbance in the background when photographing subjects; you would want either a full black background or a textured backdrop from a soft coral. This can often be achieved by positioning yourself close to the seabed.
For black-water dives, where divers drift in the open water with the dive light attached to a line, it is ideal to use a 50mm or 60mm macro lens. Focusing can be very challenging and the best thing to do is to have your buddy hold a spotlight to the critter and shut off your own. This method will also help reduce backscatter. You can set the shutter speed on high to avoid interference from other lights. Strobes can come from the side or slightly from behind to emphasise the animals.