X has had me stumped for weeks now, and for that I apologize but I promised you a posting to Light, Lines & Color (LLC) for each week this year and I will. I'm only four weeks behind! Here begins my "catch-up". We learned early this year that exposure is determined by our favorite triumvirate - Aperture, Shutter Speed, and ISO - these are the basic tools we use to create the exposed image that we want. But there are lots of buttons and dials on our DSLRs and many will help us fine tune our exposures, such as the Exposure Compensation button discussed in the post on Brightness. Now here's another helpful button for getting you to the exposure you want, it's called the Metering Button. What's that you ask?
Well let's back up a little. When you've set the camera up to take a shot, it's reading the light in the scene you've composed. You can fine-tune that reading by having it read the light in a wide area of the frame (Matrix Metering), having it read the whole frame but assigning the greatest weight to the light in the center area (Center-weighted Metering), or having it meter the light on small a circle that is centered on the current focus point (Spot Metering). On most DSLRs there's a button, easily accessible while you're looking through the viewfinder, not far from the shutter-release button that will allow you to switch between these metering settings.
Here's an assignment: Find the Metering Button on your camera. Set your camera to Aperture setting f/11, with an ISO of 100, and go out to take a landscape shot on a high contrast day, meaning a sunny day when there's a lot of shadow in the frame. Now play with the different settings on the Metering Button: Matrix, Center-weighted, and Spot, and share your reults on our Google+ LLC sight . Get to know your camera and what it will do for you.
Looking to make a silhouette shot? I like this early morning shot of my husband on a dock on the Vineyard. He was back lit in early morning light and I didn't want the camera to try to "average" out the extremes in light, so I spot metered on him, which resulted in this semi-silhouette that I love. Play with this ... it's fun.