ABSTRACT
In Chapter 4 I asked, “How sharp is ‘sharp’?” and suggested that for practical purposes “sharpness” was self-defining: if an image looked sharp, it was, ipso facto, sharp. If you felt that this was an unsatisfactory answer, you were right. But even if the detail of your image is sharp beyond this subjective criterion, if you keep on enlarging it you will eventually reach a point where further enlargement won’t show any more detail, but will simply enlarge the blur. Microscopists call this condition “empty magnification.” The point where this begins to happen is called the limit of resolution of the optical system.
