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
    Name or NavList Code:
    Email:
       
    Reply
    Re: Eyesight dangers using telescopes
    From: George Huxtable
    Date: 2009 Jun 30, 12:43 +0100

    Ken Gebhart, whom I greatly respect, asked questions with the pious "hope
    (by now) that each question can be answered with a simple yesor no, with no
    further elaboration.". I think he knows me well enough, by now, not to
    expect
    that.
    
    First, responding to a question he didn't ask, about the arucle that was
    refused (by PBO) on the grounds that  "some (small area) of British law
    prohibited publishing information on building something that could be
    injurious to the user".
    
    I'm no expert on English law, but despite its many absurdities in the
    field of environmental protection, I doubt whether any such blanket
    prohibition exists, or could be framed. It seems to me more likely that the
    publishers (or their lawyers) are attempting to justify their own timidity
    in fearing the possibility of a civil claim for damages from a litigous
    reader. For such a claim to succeed, the claimant would have to show that
    the publishers had been negligent, reckless, or at least careless in failing
    to warn of the possibilities of such damage, from which he had suffered as a
    result of following their advice.
    
    No doubt similar provisions exist in US law, with a similar distinction
    between civil and criminal law, explaining the labels we see on so many
    products attempting to absolve their makers from any liability.
    
    ====================
    
    Ken's questions take me rather outside my area-of-competence. I'm no expert
    on optics (although with a grasp of the basic physics involved). Nor am I
    knowledgeable about the physiology of eye damage, although I have a certain
    over-familiarity with the inside of the local eye hospital and the wrong end
    of a therapeutic laser. However, that won't stop me answering Ken's
    questions, as personal opinion..
    
    1.  Does normal sextant use, even by a neophyte, pose any significant risk
    of eye injury?  (I use the term significant, because we all know we are
    damaged by cosmic radiation, UV, second hand smoke, lead, beer and any
    number of other things with which we have daily contact.  I am not concerned
    with this level of danger.)
    
    Answer. Yes, by a neophyte, if he chose the wrong shade, and then, thinking
    himself protected by it, forced himself to oppose the powerful blink-reflex
    and aversion-reflex to prolong his look. It would call for some degree of
    self-destructive death-wish on his part. No, in terms of the occasional
    instant flash of light that occurs to all sextant users from time to time
    when a shade misaligns, bringing on an eyelid closure within a fraction of a
    second.
    
    2.  Does the risk of eye injury increase with the addition of a magnifying
    scope?
    
    Yes, I would say it does. Not in that the scope renders the Sun image on the
    retina any brighter; quite the reverse. But it certainly makes it bigger, so
    increases the chance that any such Sun image will embrace the sensitive
    central macular area, which it's so important to protect. On the other hand,
    all that extra total light will presumably make the blink-reflex even more
    compulsive and quick-acting.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    --~--~---------~--~----~------------~-------~--~----~
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To , email NavList-@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

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

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

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

    Email Settings

    NavList ID 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