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Anonymous
Notes on the Resolution of the Human Eye
What is the resolution of the human eye, or eye plus brain combination in people? There seems to be a lot of different numbers quoted.
Visual acuity is defined as 1/a where a is the response in x/arc-minute. The problem is that various researchers have defined x to be different things. However, when the different definitions are normalized to the same thing, the results agree. Here is the problem:
Usually a grating test pattern is used, so x is defined as cycles in the pattern. Different researchers have used a line, a line pair, and a full cycle as the definition of x. Thus, they report seemingly different values for the visual acuity and resolution. It is easy to recompute the acuity to a common standard, when the study defines what was used.
So when we define x to be a line pair, as is normally done in modern optics, the 1/a value is 1.7 under good lighting conditions. This was first determined by Konig (1897 [yes that's 1897] in 'Die Abhangigkeit der Sehscharfe von der Beleuchtungsintensitat,' S. B. Akad. Wiss. Berlin, 559-575. Also in: Hecht (1931, 'The Retinal Processes Concerned with Visual Acuity and Color Vision,' Bulletin No. 4 of the Howe Laboratory of Ophthalmology, Harvard Medical School, Cambridge, Mass.) A summary plot of numerous subjects of visual acuity as a function of brightness appears Pirenne (1967, "Vision and the Eye," Chapman and Hall, London, page 132).
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