What exactly are metering modes and why should you be aware of how they work? Modern camera's have built in light meters that measure the light in a given situation allowing your camera to select appropriate exposure settings for the scene in front of you. Selecting one of the three available metering modes will determine how your camera will measure the available light and ultimately what exposure values will be set for your photograph.
With a compact camera, being aware of what metering mode you are using (or may need to use for a given scene) is not as much of a concern - especially if you become familiar with the auto exposure lock feature. On my compact Canon camera, I always left the metering on Evaluative and made good use of the exposure lock feature to get the desired look. If, for example, I wanted a good exposure on a sunset - I would focus on different areas (watching the LCD screen for my desired look) and lock the exposure once my ideal exposure was attained. After locking the exposure I would simply re-compose and re-focus and then take the photo. This was a simple technique that allowed me to not worry about metering while getting the photo I was after.
Looking through the viewfinder of a digital SLR we are not going to have this instant feedback and ever changing view of the LCD screen like we will on a compact camera. With that in mind, understanding and utilizing the camera's metering modes becomes more important for more desirable results. Any camera will have a choice of three different metering modes: Matrix or Evaluative (Nikon uses the term Matrix while Canon uses Evaluative - other brands may differ), Center Weighted and Spot.
With Matrix or Evaluative metering, your camera will analyze the frame in its entirety and select an exposure that represents an average of the scene. This is a good default mode and will suffice for many situations. I tend to leave my camera set to Matrix for best results around the house and quick photos. The draw back of this metering type can show up in scenes with lots of contrast - you may end up with blown out highlights in the background, a subject being too dark or a bland, uninteresting final exposure. I do not recommend this type of metering for sunsets.
Center weighted metering still evaluates the entire scene, with a strong concentration on about the 75% of the scene in the very center. Areas outside of this range (which varies with brands) are given only minor consideration when selecting the final exposure. This is a handy mode to help keep your main subject exposed the desired way and aid in eliminating the influence of bright or dim spots on the outer areas of the frame.
Lastly, we have Spot metering. Like the name implies, spot metering uses a very small selection of the scene to determine the exposure. This is usually in the very center of the frame, though many cameras may allow you to select a point in the frame to use as the metering spot. I have found with a DSLR that spot metering is the best choice when taking photos of sunsets. What I will do is focus on a specific area of the sunset that I think will give me the look I am after (to get the brilliant colors to show, and usually a shadowed landscape) and use the exposure lock feature to lock in exposure before recomposing and finally taking the photo. This has yielded great results, while using Matrix metering ends up getting the landscape nicely exposed, while the colors of the sunset get washed out and over exposed.
If you find yourself switching between metering modes often, you may want to assign them to the dedicated custom function button (if your camera allows) or add them to any customized shortcut menus like the My Menu option available on Nikon's D5100.
Blessings,
Jesse
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