NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Eyesight dangers using telescopes
From: George Huxtable
Date: 2009 Jun 30, 12:43 +0100
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 -~----------~----~----~----~------~----~------~--~---