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    Re: Index correction, was: Got your book, Bruce Stark
    From: Trevor Kenchington
    Date: 2004 Nov 19, 12:50 -0400

    Alex asked:
    > Does our "day vision" have higher resolution than
    > the "night vision"?
    The fovea in our retinas, located in the centre of the field of view,
    has the highest density of light receptors but they are primarily cones,
    which are sensitive to colour but have poor low-light sensitivity. To
    detect dim light, we must use the rods (not sensitive to colour but much
    more sensitive to low light levels) which are either thinly scattered or
    actually absent from the fovea (not sure which).
    Our ability to detect low levels of light is better if the source is
    viewed off-centre, since the outer parts of our retinas have more rods
    (though still not to match the density of cones in the fovea). Whether
    or not it would be possible to use a sextant while looking out of the
    corner of your eye, I cannot say.
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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