Archived posting to the Leica Users Group, 2008/04/24
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The human eye has a focal length of about 17mm, give or take, when focused
at infinity. The lens is attached to muscles can flex, remeber. Few people
have 'f2' eyes, usually slightly slower. The retina is extraordinarily
sensitive, comparative to the recording media we use (consider that the
'exposures' are essentially instantaneous and continuous).
Focal length isn't always the same as back-focus (consider camera lenses,
which are designed to hav the same back focus but different focal lengths)
but the human eye is of fixed focal length and therefore the back-focus is
about the same as the focal length. From the cornea (the first 'element' of
the system) to the retina in most adults is about 17mm, hence the focal
length.
Marty
Gallery:
http://gallery.leica-users.org/main.php?g2_itemId=7617
Most people can only judge of things by the experiences of ordinary life,
but phenomena outside the scope of this are really quite numerous.
Shen Kuo - 'Dream Pool Essays'
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