[ATM] Spectroscopy and fiber optic info needed

[jsgrmfg at gracemfg.com (jsgrmfg@gracemfg.com)]

Hi All,

    I am deep in the design and planning process for my "retirement 'scope"
,
an equatorially mounted, computer controlled,  20" Newt. in a permanent
observatory that will get a lot of use after I retire and can, at last,
stay up
all night without hating myself in the morning.

    My observing program for this 'scope includes spectroscopy, a new area
of astronomy for me.  In particular, I would like to be able to measure
radial
velocities and red shifts with reasonable accuracy.   As I understand it,
such
measurements require high resolution and dispersion and heavy insulation
to prevent the line blurring and shifting that can result from temperature
changes during an exposure.  The spectrograph also must not shift or flex,
either internally or relative to the telescope optics.  A spectrograph that
meets
these requirements will be heavy and bulky and mounting it solidly over
the focuser of a Newt. could be a real challenge.

    It seems to me that the neatest solution to these problems is to put
the
spectrograph in an insulated box on the observatory floor and feed it
light through a fiber optic cable.  Alas, I know next to nothing about
fiber
optics.  A few hours of Googling the subject has taught me that optical
fibers
can be made from several different materials and in many diameters,
that cables may be single or multiple stranded, that multiple fibers may be
arranged in various ways, including a disk at one end and a straight line
at
the other, and that cable length should be minimized to avoid excessive
light loss.

    What I have not yet found is fiber optic information that addresses the
special needs of the astronomical spectroscopist.  Do any of the Wizards
of the ATM list have knowledge and experience in this area that they can
share with me?

    For design purposes I need to know such things as:  The best fiber
material(s)?
Single or multiple fiber cable?  Best fiber diameter?  Does the light
emerging
from the cable have the same optical characteristics (e.g., focal ratio) as
the
entering image or is the light scrambled by the fiber?  Has someone
invented a
clever way to know when the image of a star or other object is well
centered
on the fiber or fibers?

    Thanks,

Jim Sturtevant