The Parallax Problem with Your Digital Camera’s Viewfinder
A parallax error occurs when you take a picture by looking through the viewfinder of your digital camera, and the picture doesn’t look like it did in the viewfinder. On many digital cameras, the viewfinder looks out on the world through a separate window from the camera lens.
Because the viewfinder is located an inch or so above or to the side of the lens, it sees your subject from a slightly different angle than the lens does. But the image is captured from the point of view of the lens, not the viewfinder.
When you look through your viewfinder, you may see some lines near the corners of the frame (like in this figure). The lines indicate the boundaries of the frame as seen by the camera lens. Pay attention to these framing cues, or you may wind up with pictures that appear to have been lopped off along one edge.
The LCD monitor of your camera reflects the image as the lens sees it, so you can simply use the monitor rather than the viewfinder to frame your image.