Lens Shields

[Tom Droege <droege@wwa.com>]

I presently run the Mark III with long paper shields that I hang on the end
of the lenses.  This is an attempt to get rid of the stray light the
bounces off surfaces that the Mark III has to look near as it is on the
ground.  These seem to help a lot but I have no good measurements.  There
is just too much going on in my neighborhood to make any controlled test.  

Anyone have any rules of thumb about shielding the front of a telescope
like the Mark IV?  

I am presently trying to design the roll off roof house that the Mark IV
will live in.  Each inch of the light shield tends to add 3" to the
footprint of the house.  I thus want to make the shield as short as
reasonable.  Elliot once mentioned a focal length as a starting point.
This would add a lot more length than I would like to the house.

Tom Droege