NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Using any star for a lunar
From: Peter Fogg
Date: 2005 Mar 14, 17:10 +1100
From: Peter Fogg
Date: 2005 Mar 14, 17:10 +1100
In some ways the eye is like any other lens. In bright light the aperture; the size of the hole admitting light, is reduced. This gives a greater depth of field, and compared with the eye's performance in dim light, when it is wide open, colours are better perceived. But there is a limit to this enhancement, and this is diffraction. The hole becomes so small that edge effects outweigh the added depth of field - too small apertures are not efficient, as resolution progressively decreases. Most lenses give best performance at a middle aperture, not 'stopped-down' to the minimum aperture, nor wide open. ________________________________________ From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM] On Behalf Of KenJames Sent: Monday, 14 March 2005 4:36 PM To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: Re: Using any star for a lunar As for night vision and day vision, the explanation on this list in October was not accurate. Indeed, because of diffraction, the resolution of the human eye is lower in very bright sunlight than in medium lighting. This may well be true (I do not know) but I can think of one example at least where it might seem not to be so, a surgeon will use a VERY bright tightly collomated beam...maybe that is to enhance contrast or something?-Ken
