T3D vernier acuity

[Peter Abrahams <telscope@xxxxxxxxxx>]

MIL-HDBK-141, p. 4-9: The eye resolves points to about 1 arc minute, but
lines as thin as 1/2 arc second can be resolved.  Misalignment of two lines
(vernier) is detectable at about 4 arc seconds.  "Horizontally or
vertically oriented wires are seen about equally well, but when at 60
degrees or 120 degrees to the horizontal, they are only about one third as
visible".  
D. Malacara, Geometrical & Instrumental Optics, p125: Vernier acuity is
about 5 arc seconds.  A dark line 30 arc minutes in length, and 1/2 arc
seconds in width can be resolved.  A pair of dark lines are resolved as a
pair if separated by 30 arc seconds.
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Vernier acuity probably wouldn't be enhanced by binocular vision, because
you need to avoid parallax and view the two lines from directly 'overhead'.
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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