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    Re: Whole Horizon Mirrors
    From: Ken Gebhart
    Date: 2011 Apr 25, 11:54 -0500

    It should be noted that the whole horizon mirror has better than 50%
    transmissivity (say 80% maybe) through the side facing the horizon,
    and better than 50% reflectivity from the side facing the index
    mirror.  The sum of the two is not limited to 100% as it would be if
    only one side of the mirror were considered.
    
    Ken Gebhart
    On Apr 25, 2011, at 1:06 AM, Geoffrey Kolbe wrote:
    
    > At 20:44 24/04/2011, Gary wrote:
    >
    >> 50% throughput, on the average for both the horizon and the star
    >> for the whole horizon mirror. But for the split mirror almost 100%
    >> throughput of the dim horizon and almost 100% reflected of the dim
    >> star.
    >
    >
    > Ya-but.... When using a telescope of reasonable power only half the
    > light input to the scope is coming from the star and half from the
    > horizon, so there should be no difference whether whole-horizon or
    > split-mirror horizon mirrors are used.
    >
    > I can see that when using a sighting tube the eye will see an
    > uninterrupted view of the horizon on one side and of the star on
    > the other. For low power sighting systems the images will not be
    > super-imposed with a split mirror system but at least you will see
    > the star.
    >
    > But.... When trying to see faint stars, it would be better to avail
    > yourself of the increased light gathering power of a telescope -
    > would it not? In that case, does it matter which system you use?
    >
    > Geoffrey
    
    
    
    
    

       
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