9 Feb
2005
9 Feb
'05
11:38 p.m.
Quoting Brent Watson <brentjwatson@yahoo.com>:
One portion of your need to refocus comes from temperature variations in you optical tube. The gravitational effects of the sun and your thumb are positional errors, not focus errors.
But positional errors are the result of distortion which I would think affects focus.
The reason things look sharper when you hold your thumb next to them (ala Guy) is that you are reducing the effective aperture of your eye, and thereby increasing the depth of field.
That sounds about right. Thanks Brent.