Ooh! You've just discovered that your camera has a "sunset mode." No need to finish the Dash, right? Just put your camera in sunset mode and ta da! Perfect sunset photos.
You already know what I'm going to say. Your camera's scene modes are great, basic ways to quickly capture a scene with settings that are pretty good most of the time. If you've got a point and shoot camera that doesn't give you many manual functions, by all means use sunset mode. Sunset mode is designed to optimize the colors in the typical sunset scene. It will add saturation and it will account for the unique lighting conditions that you only see at sunrise and sunset. It will make a pretty good guess.
So yes, you can use sunset mode. But don't. Think of it like this: you're out walking along the beach at sunset with a friend, with paintbrush and canvas in hand. You sit down in the perfect spot on the beach so you can capture that beautiful sunset with all those red and pink colors you have stashed away in your artist's kit.
Caspersen Beach Pano by Flickr user DonMiller_ToGo
"Oh no," says your friend. "That's a terrible color. You need to use that yellow instead. And that sunset looks like it ought to have that pale orange in it too. And you need to be able to see the detail in that ugly little shack there on the beach. I know, you don't like that shack but it's there and you have to paint it exactly the way it looks."
Who's right? You are of course. That is, if you are the photographer and your friend is the camera. The bottom line is, you don't want your camera telling you how to get the best picture of the sunset. You don't want it deciding what settings will look best, because that should be your decision.
Most of the time, that sunset mode is going to get a decent photo. But what if you want the foreground to be just that little bit darker? Or what if you want to see detail in the foreground instead? You can't just tell sunset mode to tweak the image a little bit in one direction or another because it's already decided what's best for you.
The main concern with sunset mode is that it interferes with your artistic choice. Much of the time, that artistic choice is going to be concerned with how much light you add or subtract from the scene. And for sunsets, much of the time, less is more.
Underexpose to bring out those colors
Underexposing can be useful in a lot of situations, especially in scenes where there is a broad range of tones and you can't capture them all in a single shot. In most cases, it's better to err on the side of underexposing—this will maintain details in the highlights at the expense of the shadows. It also has the added benefit of saturating the colors, which tend to be washed out in situations where there is very strong light.
Mangroves at Sunset - Key Largo, Florida by Flickr user Daniel Peckham
The sunset is one of those situations where there is very strong light, except that it's concentrated in one part of the sky. When you underexpose, you'll get some foreground elements that fall into shadow and lose detail. They may even become silhouettes. But the trade-off is that you will get deeper colors where it matters—in the sky, which is where you want your viewer's attention to be focused.
Sunset from my bedroom window #2 by Flickr user jcoterhals
Two Ways to Underexpose
Use Exposure Compensation
Set your camera up for aperture priority mode and then use exposure compensation instead. Exposure compensation (usually accessed with a button on the back of your camera body) will give you the ability to add or subtract light in increments of 1/3rd stops. Setting the exposure compensation to a negative number will underexpose the shot, setting it to a positive number will overexpose. Take a series of images with different EV values and keep the best.
Most of the time, you're going to find that slight underexposure gives you the best results, but that really depends on your artistic choice. The more you underexpose the richer and more saturated your colors will be—to a certain degree. But as you underexpose you also lose detail in the foreground. That may be fine—you may actually want your foreground elements to appear as silhouettes. But if you don't, you'll need to underexpose less to bring out the detail in those areas.
Use Manual Mode
Once you know how to use manual mode, nothing could be simpler than underexposing a shot, except maybe over exposing it. You can even accomplish this pretty easily in one of the semi-automatic modes, such as shutter or aperture priority.
Sky and Colors of Sky by Flickr user ...anna christina...
First put your camera into manual mode and then have a look through your viewfinder. You'll see a little gauge in there with a "0" in the middle, and a "+" and "-" on either side. If you shoot in manual you're already familiar with this tool because it's what allows you to make a judgement about your exposure. Most of the time, settings that place the needle at "0" are going to result in the correct exposure. But when you're shooting a landscape, you may find that a needle that falls somewhere between "0" and "-" is going to give you the best results. The "-" simply means that your camera's meter thinks you're underexposing the shot. And you are, at least by 18% gray standards. But for a sunset, underexposure is often the correct exposure.
Sunsets are dynamic situations, which means that the light is changing pretty rapidly and it can be difficult to gauge accurately from one shot to the next. Here's where bracketing comes in handy—check your LCD after that first shot, then either add or subtract light by slowing down or speeding up your shutter speed. Gather a half dozen shots at different exposures and then compare to see which one gave you the best results.
mammatus cloud sunset by Flickr user SaturatedEyes
The sunset only happens once a day, so be ready for it. Don't trust your camera's sunset mode to do this for you, because the sunset is never going to look the same way it does at that one moment. If you don't get it right when it's happening, you've missed out. Just remember to start by underexposing a little and to trust your artistic vision: you have way more of that than your camera does.