Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Logic of shades
    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.
    -----Original Message-----
    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of alexander duytschaever
    Sent: 26 October 2018 17:16
    To: francisupchurch---.com
    Subject: [NavList] Logic of shades
    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?
    (*) 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
    View and reply to this message: 

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site