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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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