Have you ever looked out at a beautiful snowy landscape thinking what a wonderful photo it would make, then after taking the shot you ponder why it turned out so flat? Well, you can pretty much blame the way the camera's metering system works for this outcome.
Let's use a simple example to understand what is happening. Before us is a landscape covered mostly with snow, a cloudy (thus white) sky and some trees also mostly covered with bright white snow. To our adaptive vision, all is well and the snow is a brilliant, almost blinding, white and the shadow areas of the scene (trunks of trees and exposed rocks on the hillside) are full of many interesting minute details. But to most cameras, this scene is averaged into a boring middle gray tone with care taken not to blow out the highlights.
You happily press the shutter button to capture this moment in time, only to discover that the image looks quite noticeably darker. You then begin to pout, take a sip from your hip flask and consider if life is worth living. Ok... maybe it's not that bad.
Before moving on, here's a fun and quick experiment you can try on your own to see the metering system in action. Grab your camera and head over to your computer. Open up an application with a lot of white in it like Notepad or Microsoft Office. Point your lens at the monitor, zoom in so all you get is white in the frame and with manual focusing on, ensure the screen is not in focus (if you use autofocus then the camera might focus on the pixels on the screen; we want a diffuse white instead and that's also why we're using a monitor as the brightness is more even compared to a lit white wall for example). Use a common mode on your camera such as aperture priority without any exposure value (EV) compensation and take a picture (although this should also work with shutter priority and automatic). What you should see is a grayish image, not white!
What Can be Done and Why
As you can probably guess from the last paragraph, you can employ the EV compensation feature on your camera to over-expose the photo (the EV button is the one with the little "+/-" sign in a square). This may sound a little odd perhaps to over-expose what appears to be a very bright and white scene, but taking into consideration how the metering works, this should make sense. Over-exposing may also be the wrong terminology to use here, because you're actually adjusting the camera's values to attain a proper exposure; over-exposure generally means blowing out bright areas of a photo. Now all cameras differ to some extent so you will have to experiment a bit to discover how your machine behaves, as you may require more or less compensation. Towards the bottom of this post you'll find some photos I took so you can see how my camera (Olympus E-P2) behaved at various settings. Note that even at +1.0 EV, no highlights are blown (according to the histogram in Photoshop CS4).
Before moving on, I do wish to add that I almost always have my cameras set to center weighted metering. I have found with experience that I get fairly consistent and reasonably good results with it compared to the area or multi-metering style (which uses numerous points all over the frame). Perhaps try experimenting with both settings to see the differences you get. As for spot metering, I use that option quite rarely and usually for special cases.
But why use EV compensation? Some of you out there might be shooting RAW and are thinking that you could just pump up the exposure in an image editor; even if you're shooting JPEG you could increase the brightness. To a certain point this may be true, but software can never truly replicate what would've happened if the image was better exposed for real. And if there are very dark areas of the image present, then detail in those zones may be permanently lost... even if you're saving photos in RAW format. Black is black and you can't do much with that. I also find that more noise and graininess comes forth when using software to modify the exposure of some under-exposed images.
Another benefit to using EV compensation in such cases is that you won't need to edit your photos as much. Personally, I've always like the mindset of shooting right first, versus shooting messy and fixing later. Thus, unless you need to use RAW for whatever reason, you might be able to use the JPEGs right out of the camera with minimal after-work. Time saved is definitely a pro, whether you are doing photography for a living or just want more time for other hobbies like wood carving.
So in summary, by using that good old EV compensation button you can make images more pleasing by enhancing their contrast, improving details in shadow zones, making colors more vivid, all the while decreasing edit time. Of course in some cases there may be artistic reasons you would deliberately want to under-expose shots (heck, you can use negative EV!) and for the HDRI fanatics out there, this is hardly of much importance due to the huge dynamic range captured in several shots which are combined (if you want to know more about HDRI, check out episodes 25, 25A and 26). Lastly, not just the wintery and snowy shots benefit from a little compensation. If the scene you are shooting doesn't have a large contrast between light and dark (think landscape with a bright sky and dark ground), but instead has a more even luminance (colorful leaves on the ground; flowers against dark foliage), then increasing the EV might improve the shot, especially in regard to color (this was fairly noticeable in the shots I took of Daisy).
So I hope this simple tip improves your photos and gets you experimenting with EV compensation, especially if you haven't used it much.
Also, wherever you may be, I want to wish you and your families all the best for this season! May your celebrations be merry and filled with happiness, and all your photos come out of the camera perfect... and if they don't, then label them "art" or "abstract". :) L8r!
Photos below are linked to full size versions in my Flickr Photostream.
Logs at 0.0 EV
Logs at +0.3 EV
Logs at +0.7 EV
Logs at +1.0 EV
Pine Tree at 0.0 EV
Pine Tree at +0.3 EV
Pine Tree at +0.7 EV
Pine Tree at +1.0 EV
Daisy at 0.0 EV
Daisy at +0.7 EV