The minimum would be one arc minute for stroke width and a five arc minute height for characters if they are to be legible. This is the basis for 20/20 vision (resolution or visual acuity) on eye charts. I would think that you would want to at least double this. One can detect and determine the location of a shadow that is narrower than this. I seem to recollect that power lines can be detected against the sky when their width is perhaps five or ten arc seconds.
Gordon At 06:55 PM 2/10/00 -0700, John Carmichael wrote:
Good dialing question Ross Caldwell! (We might need an optomologist for this one.) John Carmichael >You write: > >Do you know of any kind of formula to estimate the proper proportions for >seeing high or distant dial lines, letters etc. clearly? I suspect >architects, engineers and advertisers (billboards) must have some way of >knowing what will be clear to a given eye at a given distance. > >Ross Caldwell >[EMAIL PROTECTED] >119 48 11W >36 46 14N >Fresno, CA USA
Gordon Uber [EMAIL PROTECTED] San Diego, California USA Webmaster: Clocks and Time: http://www.ubr.com/clocks
