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Answer
Stumper #22Question:
When I took a picture of a mirror in which the reflection
showed me taking the photograph, the result was a mirror in perfect focus and my
reflection distinctly blurred. Why was my reflection not in focus?
Answer:My reflection in the mirror was a "virtual image" and the distance at which it would be in focus would be twice the distance of the mirror frame to the camera. It was therefore not possible to have the mirror frame and my reflection both in exact focus at the same time if I was standing close to the mirror.MORE:
In order to have both the frame and my reflection in focus I should have positioned myself so that I could set the camera to focus at close to infinity. That way everything would be pretty much in focus.
To explain the matter in terms of physics you need to understand that the virtual image is located behind the mirror at a distance equal to the distance from the camera to the front surface of the mirror. So, the distance between the camera and its image is 2x the distance between the camera and the mirror frame. Therefore it is necessary to focus behind the mirror not on the mirror.
To find out about mirror reflections and virtual images you might look at the following references:  Useful for ages up to twelve For teens and adults: (An interactive java applet optics experiment written by Asso. Prof. Fu-Kwun Hwang Dept. of Physics, National Taiwan Normal University)
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