CHAPTER 11 What Is an Equivalent Image?
Distinctions drawn by the mind are not necessarily equivalent to distinctions in reality.
—THOMAS AQUINAS
Size matters not. Look at me. Judge me by my size, do you? Hmm? Hmm. And well you should not. For my ally is the Force, and a powerful ally it is.
—YODA
11.1 Introduction
The advertisements for digital cameras usually state that the lens has a focal length range “equivalent” to a certain range on a 35 mm camera. One “expert” tells us each lens has a focal length and that it is not equivalent to any other focal length regardless of the circumstances. Another expert claims that a big sensor is necessary to get a small depth-of-field. These are at best half-truths. So, what is correct? In ...
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