Pointing your camera directly at a sunset produces a dramatically underexposed result because the camera's metering reacts to the intense bright light. Sometimes this can look good, especially if you have a good silhouette but once the sun actually sets below the horizon you are left with less colour and no tone in the your subject. One neat way to boost the shot and make your subject appear almost three dimensional is to pop a bit of fill-flash into the scene. You can do this using a small pop-up flash or a larger speedlight.
Set the camera on a tripod and in Manual (M) metering mode establish the base exposure - do this in Program mode, then copy the exposure recipe into manual mode. A good sunset fill flash exposure is one that produces a nice, rich sky colour.
In this example it was 1/250s because the light from the sunset was quite bright. Most might automatically set a slower shutter speed because you are technically shooting at night, right? No, a faster shutter underexposes the night sky and produces rich colours.
It's important then to keep the aperture wide open, or close to wide open, so the flash can make a mark on the subject. Most flashes are only effective at eight to ten feet with a small aperture number (i.e. f4 - 5.6). If the aperture is set smaller (i.e. f16) it makes a huge demand on flash power - which a pop-up flash doesn't have. If using a speedlight, firing at full to half power will exhaust the batteries fast.
As the sky gets progressively darker, raise the ISO which will also help the flash maintain its brightness.
So the lesson to be learned here is that shutter speed always controls the brightness of the ambient light while the aperture always regulates the brightness of the flash...
|Sunset with no fill flash produces a nice effect but somewhat hard, black silhouettes.|
|Sunset with fill-flash. 1/250s @ f4, ISO 640|
|Another successful and fun location at Broken Hill's Living Desert reserve 9kms out of town|