One of the biggest challenges photographers face is night portraiture. In essence you're trying to solve two problems; one is getting a portrait correctly, and the other is to properly illuminate both your subject and the background.
Typically, a modern camera's logic will invoke the use of flash when light levels drop precipitously. That's good because your subject will be visible.
But take a second look at the image above. Notice that while your subject is well illuminated, the background is blown to black. This is the Deer-In-Headlights look, where the flash has overpowered the background or available light. If you stay still long enough in a dark area, your vision will adjust and you can see a lot of detail even if the only light available is very low. The problem is that in order to capture that on a camera without a flash, you have to stay still for a long time and so do your subjects. Adding a flash without calculating for that background light just blasts any detail beyond the subject into pixel oblivion.Recent camera automation solved this problem by using a special "Night Portrait" mode (depending on camera model, the title may vary - it's also popularly known as Night Scene). How does it work? It automates a technique that has been well known to manual control photographers - if you slow down the shutter speed of the camera while firing the flash, you can get both the subject properly illuminated AND bring the background details (excuse the pun) to light.
As the example above reveals, Hogwarts Castle at Harry Potter's Wizarding World was in the background the whole time.Photographers with manual control cameras can recreate Night Portrait mode as well. All it takes is the ability to drop the "synch speed" or the shutter speed at which the camera will fire while activating the flash. In this case, It was 1.3 seconds. Note that the duration of the flash firing is not meaningful - it's how long the shutter stays open after the flash fires that allows us to illuminate both foreground (subject) and background.
Caveats:
Your subjects must stay still. This is true if your are using Night Portrait or the manual method. Any movement is likely to end up being captured as a blur. In the 2nd photo above, you can see a bit of "ghosting" on the edges of my subjects because 1.3 seconds is an eternity in flash photography, and there is plenty of opportunity for natural movement to be captured even though your subjects may feel they are standing still. My shaky hands didn't help either. The blurring effect was off-set by my use of an Image-Stabilizing lens, so this technology can help if it's available to you.
You may need to reduce the amount of flash being fired. This may not be available to cameras only equipped with Night Portrait mode, but for cameras with manual controls, you may need to reduce your flash power from what the camera thinks is the right amount. In this case, I had to reduce flash power by two full stops (-2.0 EV) because the flash was still blowing out the background.
As always, happy clicking!
