What is the maximum size of content the human eye can focus upon on a computer screen?
Is there a general equation that gives this size as a measure of distance from the screen etc.?
What is the shape of this focus area- is it a square? a circle?
2 Answers
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The fovea (highest-resolution area of the retina) can only "see" the central two degrees of the visual field; the field of foveal vision is approximately circular, although it varies slightly by individual. This depends on the distance from the eye or sensor. This is called "visual angle" or "angular size", and it can be calculated using the formula
where S is the object's linear size and D is the distance between the eye/sensor (sometimes called point O) and the object.
More here: http://en.wikipedia.org/wiki/Visual_angle
Calculator here: http://www.oocities.org/robertellis600/va.html
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When you extend your arm and look at your thumbnail, that is approximately the area that is focussed ("sharp") in your field of vision (about 2°). Your vision is sharp only in your fovea. Your attention can "focus" on other areas in your field of vision, although they are and remain blurred.