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: Sextants with Polarizing filters
    From: Peter Fogg
    Date: 2006 Jan 25, 08:32 +1100

    > From: Frank Reed
    > ... the idea is to use crossed polarizing filters
    > which can be rotated to produce any desired  amount of darkening
    > (within a certain range)...
    Sounds like a good idea. On the certain range: each polarising filter
    reduces the brightness of light passing through by about one and a half f/
    stops, or 150% (this varies between manufacturers; 150/200%). So two used
    together would already have quite a significant minimal darkening effect,
    which could be halved by using only one. The maximum effect is complete
    opacity; no light gets through - try it with a couple of pairs of polarising
    A great advantage is that polarising filters significantly reduce glare,
    just what you want reduced when trying to pick out the horizon against
    sunlight glittering off the sea. I think polarising sunglasses are the best
    sunglasses for on-board use. Another reason is that by reducing reflections
    from the surface of the water they allow you to see more clearly below the
    surface. Just one head of coral unseen can ruin your whole day ...

    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