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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Wharton & Field's Hydrographical Surveying
From: Fred Hebard
Date: 2004 May 9, 23:34 -0400
From: Fred Hebard
Date: 2004 May 9, 23:34 -0400
On May 9, 2004, at 4:52 PM, Robert Eno wrote: > Fred Hebard wrote (a quote from Wharton & Field's): > >> For these observations in an artificial horizon, Wharton recommends an >> eypiece shade rather than the swing-out sextant shades. He also >> recommends multiple eyepiece shades of varying optical density. He >> discusses examination of errors caused by swing-out sextant shades. >> > > Robert responds, > > I don't know if I buy the bit about swing out sextant shades > introducing > errors. Perhaps this was true back when that book was written, however > can > the same be true for modern sextant shades? and Fred: You bet. I heard of an example not too long ago of a modern, "quality" manufacturer who shipped un-parallel shades. The eyepiece shade avoids any swinging shade effects, including ones that aren't there :) At appropriate altitudes, swinging shades also will reflect a pretty strong image of the sun right into the field of view. Fred