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: Horizon Shade Polariser
    From: Francis Upchurch
    Date: 2016 May 7, 00:40 -0700

    Thanks gentlemen for the reassurance  on this.

    I suspect if you are just using it for horizon filter, no problem anyway. Chronic UV light exposure is mainly associated with  long term risks like macular degeneration and cataracts.

    However, acute damage from looking directly at the sun through a telescope (i.e the index mirror on a sextant) is more likely related to the infrared end of the spectrum. You can literally burn a hole in the retina like starting a fire with a magnifying glass!

    So, I would want any index filter to stop both UV and infrared. Also , hence the advice from Astronomy  web sites for observing eclipses, transits etc.,  to put the solar filter over the  main primary lens of the telescope, not the eye objective. You can easily burn a hole through the eye objective filter and then the eye! I've now stopped using the simple and for the eye, the safe method of direct projection of the sun image onto a white screen.This  is safe for the eye, but actually, not for the telescope which can get pretty hot and if the focus goes wrong, you could easily start a fire with what is essentially a very powerful magnifying lens!

    Sadly, it looks like mother nature is going to protect my eyes on Monday by placing thick cloud filters in front of the sun. So I hope someone else out there in sunier climes will do some Mercury transit observations?

    Safe sungazing!

    Francis

       
    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