NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Vernier acuity" of horizon IC tests
From: Frank Reed
Date: 2009 Jul 6, 23:39 -0700
From: Frank Reed
Date: 2009 Jul 6, 23:39 -0700
Bill M, you wrote: "In the SNO-T horizon mirror, there is a narrow band of paint overlap, about half a millimetre, on the back of the mirror extending on to the clear glass. This is true ( or should be true) of most sextants, as the paint protects the edge of the silvering. Exceptions might be those instruments with sealed mirror cells. Its relevance is not clear to me." Unfortunately, the relevance is that it apparently no longer qualifies as a vernier acuity task if there is a gap between the two sides of the field of view. I'll have to try out the full range of sextants I have available tomorrow and see if there's a significant difference for the different type of horizon glass cells. But clearly, for that sextant, your results do not demonstrate ANY evidence of vernier acuity. It's normal acuity. So, in this case, better results would necessarily be obtained with a telescope than without. This "strange trick" may be a lot less common in practical cases than I would have guessed. -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---