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Frank,

The one polarizing-shade sextant with which I have worked had
noticeable shade error.  I didn't try to measure it carefully, but
noticed enough of it to conclude it was large (on the order of 30" of
arc).  I'll leave the physics to you!

Fred


On Feb 6, 2006, at 6:12 PM, Frank Reed wrote:

> Joel Jacobs, you wrote:
> "MAYBE THE BIG  BUGABOO IS THAT WHEN SUBJECTED TO SALT SPRAY THEY
> TENDED TO
> FREEZE AND ALSO  FROZE IN FEARCELY COLD CONDITIONS.. AND INTRODUCED
> ABOVE
> AVERAGE SHADE ERROR  OVERALL."
>
> Regarding salt spray and freezing, I think you've hit the nail  on
> the head.
> I have noticed that they stick hard in cold weather. I suspect that
> polarizing filters seemed like a nice "high tech" innovation 60
> years ago, but  in
> practice easy maintenance won the day.
>
> As for shade error, I can't  think of any reason why polarizing
> shades should
> have greater error in general.  And since the elements rotate, if
> there
> really was greater shade error, it would  also be variable!
>
> -FER
> 42.0N 87.7W, or 41.4N  72.1W.
> www.HistoricalAtlas.com/lunars

   

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