Eowyn: I agree To calculate the correct angle to take a reflection render from, determine the angle that the camera's line-of-sight makes to the surface of the mirror, then make that negative (or subtract it from 360, same thing). For instance, if the camera's line of sight is at a 45 degree angle to the mirror, the reflection camera should be placed at a -45 degree angle (AKA a 315 degree angle) to the mirror. With a mirror that's actually got a pand of glass in it, when rendering the actual view place a copy of the mirror right behind it the distance of the thickness of the glass, with all the materials transed out except the glass, and the glass set to a bright ambient blue or green for easy selection in Photoshop. This will create a 'bluescreen' effect behind the mirror. When the reflection render is shot, remove the copy of the mirror and shoot through the glass. Anything on the glass like dust or scratches will then let you line up and scale rhe render perfectly. If the mirror is perfectly clean or there is no actual mirror surface, you have to use the edges of the mirror itself. Remember that a mirror will reflect within it the frame of the mirror itself.