T3D eyepieces

[Peter Abrahams <telscope@xxxxxxxxxx>]

John, The post made sense all right.  The physical model, of taking a
section of the sky 1 degree in diameter & magnifying it to as much as 80
degrees, while retaining angular relationships, is what I think of.  The
'decision' to make low angular distortion the goal can seem arbitrary; the
idea is that if 3 stars form an equilateral triangle at the center of the
field, they should show the same at the edge of the field.  It isn't writ
in stone that this quality is more important than low field curvature, for
example.  Or, if you're viewing a city during the day, low linear
distortion might be a better goal, since with an ocular that causes
straight lines to seem curved, panning across a scene  can cause nausea.
These discussions are typically about astronomical oculars, which are
really rather specialized.
  The $250 Celestron ocular, with low distortion, might have had a good
amount of field curvature.  Nagler's Televue eyepieces have very low field
curvature, and are sharp almost to the edge, but they do have linear
distortion.

What article on eyepieces were you referring to?
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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