This could be the reason your photos are coming out dark: light is entering the camera from the back. Precisely, it’s entering through the viewfinder and messing with the camera’s ability to accurately read TTL light levels. Ever notice that little viewfinder cover that’s probably attached to your camera strap? I didn’t think so. Well Peter West Carey at Digital Photography School did notice it, and he’s put it to good use to help prevent erroneous light from affecting his photos. You don’t have to use this little device to eliminate light from the viewfinder, you can also use your hand, or your eye, or just about anything else to block light from leaking in while the camera is calculating exposures. Read all about how and why this works at Peter’s great DPS blog post.