Metering is a broad topic. Discussions could go on for hours if you wanted to dig into the technical aspects, but for the purposes of this article, we'll simply be focusing on the three main metering modes available on most modern DSLRs. On your camera, you'll probably have a small selector dial with three options on it; a single, tiny spot, a larger spot with a thin band around it, and an even larger spot with a full border around it. This will obviously vary from camera to camera, so consult your owner's guide if you're having trouble figuring out where you metering toggle switch is. Below, we'll discuss the three primary modes and give you examples of when you should (or shouldn't) use each one.

Be aware that these only automatically adjust when using the camera in a mode other than 'Manual.' If shooting in manual mode, you'll have full control over the metering prior to shooting each shot, so you'll need to make adjustments based on what your camera says; in other modes, the camera will determine the metering for you based on which of the below selections you have made.

Spot Metering. This is that tiny circle we referred to above. If you select this, your camera will only focus on a very small portion of a shot, which you can direct in your viewfinder. The camera will then adjust exposure for only that, and ignore the surroundings entirely. If choosing a spot that isn't an obvious focal point, you'll need to manually focus. When is this useful / not useful?

• Use spot metering if your subject is brightly backlit, and you have no real concern for the background being "blown out," or appearing white, so long as your subject is exposed properly.
• In macro shots, spot metering can be useful to get the exact exposure on the objects in the center of the frame.
• If you're attempting to photograph the moon, spot metering accurately disregards the expanse of black around the moon itself.
• If you have a landscape shot with lots of shadows, you can adjust the spot so the camera exposes for a non-shadow.
• Don't use spot metering if you have any concern at all about the entire image being exposed properly.

Needless to say, spot metering is a niche option. It's only useful in a handful of situations, so it shouldn't be your go-to selection. Moving on, there's a Center Weighted Average Metering option. Think of this as the "splitting the difference" option. In a nutshell, this will average the exposure of the entire frame, but give extra consideration to the center area of the image. When is this useful / not useful?

• For portraits -- maybe a couple on a beach, or a family at dinner -- this option works well.
• If your subject is brightly lit, but you do care about the background (a cityscape behind them, for example), give this option a whirl.
• If you find that your Matrix metering option isn't providing accurate suggestions or giving you enough control over what is focused on, this weighted option might be the ticket.

Matrix Metering takes the entire image into consideration and exposes accordingly.

The final major mode found on the bulk of DSLRs is Matrix Mode. This is both the most complicated to explain and (in general) the most useful. Each camera handles it differently, but the idea is that multiple zones are evaluated, and then all of them are weighted together and evaluated as a whole using algorithms that you probably have no desire to understand. Just trust us: these algorithms are usually very small, and oftentimes provide the best direction for exposing shots where the entire frame is important to consider. When is this useful / not useful?

• The rule of thumb is to always use Matrix mode unless you can think of a specific reason why you'd need Center Weighted Average or Spot Metering modes.
• Even if you think Spot or Center Weighted modes would be useful, we'd recommend shooting first in Matrix. Today's DSLRs are surprisingly good at judging exposure based on calculated matrixes.

Keep in mind that this is just a basic explanation of metering to get you started. In future articles, we will cover tips on how to use changes in metering for creative effects in scenarios related to travel. For example, selecting the best metering mode for snowy vacations, or for capturing macro shots of foods or signs that'll remind you of your journeys. Hopefully with the pointers listed here and in our previous articles on ISO, aperture and shutter speed, you'll be four steps closer to understanding your camera's 'Manual' mode.

Let's recap:

• Metering is important because it determines the exposure of your shot, or how brightly / dimly lit it will be.
• Use Matrix Mode on your DSLR unless you have a very specific shot or reason to use another option.
• Spot Metering is useful only in niche circumstances, such as brightly backlit sporting events, shooting the moon or certain macro shots.
• Center Weighted Average Metering is best reserved for portraits.
• Even when metering, you can (likely) adjust your exposure up to two full stops in either direction; since Matrix is the least predictable, be willing to tweak things a little brighter or darker depending on preference.
• If you're overly concerned about metering, but have little time to adjust things on the fly, shoot in RAW -- metering can largely be adjusted after the fact with no real deterioration of quality if you do so. With JPEG, you will notice a decrease in quality when dramatically changing the exposure in post-processing.

Stay tuned for more tips on understanding metering, white balance and more! Our basic guide to understanding ISO, aperture and shutter speed can be seen here.