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: Robert Gainer
    Date: 2006 Feb 7, 09:28 -0500

    What I consider my best instrument is a Cassens & Plath sextant that has gray 
    filters and polarizing filters for both the index mirror and the horizon 
    mirror. Because of the recent conversations about the errors inherent to the 
    polarizing filters, I put this instrument in a table top stand and cycled 
    though the range of adjustment for both polarizing filters while focused on a 
    roof top over a mile away. I must admit that I cannot see any displacement of 
    the image as I turn the filters. If there are any errors, they are smaller 
    then my eye can see and of course, that is as precise as the instrument needs 
    to be for my use.
    I do however now have some ?fog? between or maybe I should say inside one of 
    the polarizing filters. This may be caused by keeping the sextant in the car 
    overnight to see if the cold stiffened up the adjustments and action of the 
    instrument and then bringing it inside to test the errors in the filters. I 
    had not considered the use of the sextant in cold weather until cold weather 
    was mentioned in a recent posting and my trip to North West Greenland next 
    year will mean using the sextant in a colder environment.
    First, how do you clean inside a polarizing filter and second because the 
    action did stiffen up from the cold how can I ?change? the oil to a winter 
    Robert Gainer

    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