You are using a mirror and a camera to make a self-portrait....

You are using a mirror and a camera to make a self-portrait. You focus the camera on yourself through the mirror. The mirror is a distance $D$ away from you. To what distance should you set the range of focus on the camera?
a) $D$
b) $2 D$
c) $D / 2$
d) $4 D$

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Key Concepts

Camera Focusing and Effective Distance

This principle involves understanding that a camera lens must be focused at the distance where the subject (or its image) appears to be. When using a mirror, the effective subject is the virtual image formed behind the mirror. Therefore, the camera should be focused at twice the actual object-to-mirror distance, which in this case is 2D. This understanding of effective distance is crucial in setting the correct focus for clear imaging.

Plane Mirror Image Formation

This concept explains that a plane mirror produces a virtual image that appears to be located behind the mirror at a distance equal to the distance from the mirror to the object. In problems like this, although the object is D away from the mirror, the light path behaves as if the object were located 2D away (D to the mirror and D from the mirror to the image), which is key to determining the effective distance to focus upon.

Transcript

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