NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Logic of shades
From: Francis Upchurch
Date: 2018 Oct 27, 07:35 +0100
From: Francis Upchurch
Date: 2018 Oct 27, 07:35 +0100
Welcome aboard! I think visual acuity varies with colour (i.e. wavelength of light). The colour sensitive cone cells are more sensitive to green than to blue I believe. Red is poorly perceived in low light. I am not sure if this is any basis for the logic of shades. Francis -----Original Message----- From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of alexander duytschaever Sent: 26 October 2018 17:16 To: francisupchurch@gmail.com Subject: [NavList] Logic of shades Hello, I'm a n00b user/amateur astronav that dived into astro navigation after stumbling over a Bris sextant and wondering if one could ever perform LOP calculatons using a slide rule (got a few of those) :-) (*) So I soon acquired a small shiny King Hughes 1917 replica and recently a Davis Mk 15, and I can happily live with their shortcomings (found an article on how to deal with those shortcomings, and I still have to calibrate these three). My question is: what is the logic behind the different shades? I understand that one needs more shades for the index mirror (4 vs 3 for the horizon), but why were those colours (blue, blue, orange, grey) chosen? I suspect that the light grey colour can be used for moderate lighting or to increase contrast, and it also reminds of lunar light conditions; but the two blue glasses look similar (I guess a main function is to block out UV), but are there intended ways to combine those glasses? thx -alex- (*) for now, my answer is that a SR can serve for interpolations; it doesn't have enough digits to provide sufficient accuracy. or maybe with A LOT of sightings, who knows... [plain text auto-generated] ---------------------------------------------------------------- NavList message boards and member settings: http://fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3.com ---------------------------------------------------------------- ---------------------------------------------------------------- : http://fer3.com/arc/m2.aspx/Logic-shades-duytschaever-oct-2018-g43167
