If you’ve ever taken a flash photograph at night, you probably know first hand how cold and unnatural these kinds of photographs can look. What you often end up with is an overexposed photograph of a person floating in a sea of black space. But there is a better way to make a portrait at night, the subject of this week’s Weekend Assignment.
When the light starts to go dim, your camera compensates by opening the aperture and decreasing the shutter speed. But when it is truly dark, it wants to use the flash as the primary light source for the scene. The problem is that it will probably also switch back to the default flash sync shutter speed of 1/60s. At that speed, nothing in the background will be exposed and will be rendered completely black. That can be a neat effect, but often you want to provide some context by including the background in the photograph.
The simplest way to do this is to select the Night Portrait mode on your camera. It probably looks like a face with a moon or stars next to it. What this does is select some exposure and flash settings for you that balance the background lighting with the flash output. When you select this mode, you should notice that your shutter speed has dropped from the sync speed of 1/60s to something much slower. Your flash is now operating in “slow sync” mode. Basically, a mode that lets the flash fire with a slow shutter speed. If your camera doesn’t specifically have a Night Portrait mode, it probably has a Slow Sync flash setting.
Because the shutter speed is slow, you need to minimize subject and camera movement. It’s not super critical because the flash is still going to pop and freeze the foreground. But camera movement will make the background blurry and you may see some motion trails from foreground subjects.
Speaking of light trails, if you’ve got moving objects in the scene that are lit by the flash (vehicles, for example), you may find when using this technique that they appear to be moving backwards! To understand this you have to understand the sequence of events when you press the shutter: the aperture stops down, the shutter opens, the flash pops, ambient light exposes the film/sensor, the shutter closes. This is called “front-curtain sync” because the flash happens at the very beginning of the exposure. That exposes the moving object with a bright light which freezes it in the frame; but because the object continues moving through the exposure, the dimmer ambient light will expose the movement as a motion trail in the direction the object is travelling. The solution to this is to change your flash to use rear-curtain (or 2nd-curtain) sync. Then the sequence is: aperture stops down, shutter opens, ambient light exposes the film/sensor, flash pops, shutter closes. If your camera has a Night Portrait mode then it’s probably smart enough to stay in slow-sync with rear-curtain sync. But you might need to select a “slow rear-curtain sync” mode if you have one.