Page Robb 19-Apr-2010 Physics 140 Professor Stoddard Chapter 15 Problem 1 Ques. Your camera has a 35mm focal length lens. When you take a photograph of a distant mountain, how far from that lens is the real image?
This requires an understanding of three values: Object distance which is the distance between the lens and the subject or object. Image distance which is the distance between the lens and the real image it forms. Focal length which relates the object distance and the image distance. This relationship is referred to as the Lens Equation, and essentially means the farther an away object is, the closer to the lens its image forms (pg. 524). As an equation, it can written as such:
1 1 focal length = object distance +
1 image distance
According to the textbook, the image distance for a distant object is equal to the focal length of the lens (pg. 524). Therefore, a 35mm lens (for a traditional film camera*) is a small (wide-angle) lens, and the real image formed will be bright and small and equal to the focal length of 35mm.
1 i
=
1 f 1 = 35
1 o
= 35mm
* Note, a 35mm digital lens is roughly equivalent to a 50mm traditional (normal) film lens.