Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Fogging Optics
    From: Brad Morris
    Date: 2019 May 14, 00:46 -0400
    Tony

    Perhaps a first look at why condensation occurs.   When water vapor encounters a cool surface, the vapor can turn into droplets, which coalesce onto the cool surface.  Its a function of the dew point

    Let us assume that you have properly acclimated your sextant to the ambient temperature.  That is, you let it warm up / cool down to the outside temperature.  That's standard advice, so please do so.

    Your sextant telescope, held to the eye, leaves the horizon mirror directly in front of your presumably warmer breath.  Moist too.  So as you blow warm, moist air from your lungs directly onto the cool mirror, condensation can occur, when at the dew point.

    Anti-fog coatings can help, but so will plenty of airflow.  Keeping your mirror crisply clean will help too.  Holding a sextant endlessly to your eye can be tiring.  Not holding it there will reduce the condensation as there will be plenty of ambient airflow and less human breath on the mirror.  For lunars, take Frank's advice.  Look thru the scope, take the sextant down from the eye, adjust the sextant, and then back up to the eye.  Use both hands to hold the sextant up. Short bursts of observation with intermingled with rest / adjustment is far less fatiguing and, in your situation, will reduce condensation.

    Of course, you could always just stop or minimize breathing during the observation.  Please remember to resume breathing at the appropriate time! :)

    Brad



    On Mon, May 13, 2019, 1:17 PM Tony Oz <NoReply_TonyOz@fer3.com> wrote:

    Hello!

    Almost a year ago Rob Hansen asked how could one prevent optics from fogging. Seems nobody replied.

    Yesterday I tried an evening twilight sighting and was in difficulties because of the mirrors fogging. I wanted a Moon-Pollux lunar...

    Any hints or advises?

    Regards,
    Tony

    60°N 30°E

    View and reply to this message

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    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