[Tfug] OT: Optics

[Bexley Hall]

Hi,

Pretty far off-topic but perhaps someone can shed
some additional light on this...

I tore apart a (broken) scanner the other day to
see what was inside, etc.  (hey, if it's already
broke, *I* can't do much more damage!  :> ).

I was intrigued by the number of *mirrors* inside
it!  And, soon realized they must be concave mirrors
cascaded to act as a focusing lens (i.e. to take
the ~9" wide scan line and map it onto the ~0.5" CCD.

Of course, a lense could do the same thing -- but,
not *practically* (in this sort of application).

And, I also have a vague recollection (from a high
school physics class 794 years ago) about lenses
causing color distortion (?)... "fringe effect"
(sorry to be vague but those neurons haven't been
fired in many years  :<  )

Can someone clarify this?  I.e. aside from the
practical aspects of using mirrors being more
mechanically manufacturable in this sort of a
package, what *other* advantages they might have
over the naive approach of a lens?

Thx,
--don

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