Archived posting to the Leica Users Group, 2000/09/13
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Sun, 10 September 2000, "Alan Hull" wrote: > <SNIP> > > As for the inertial properties of various weights of sextants, there > was this guy named Newton who mentioned that an object at rest tends to > remain so. I have found that a lighter object will be easier to start > moving than the heavier and therefore more difficult to hold steady so > I’ll stand by my preference for a heavier sextant in a seaway when the > boat is leaping around. > Weight (or more precicely, mass) is a big factor in resistance to shake but a more complete description of an object's resistance to shake is the angular moment of inertia, calculated as the mass multiplied by the moment arm. Given idential moment arms, for example a camera or sextant held at the eye, the heavier one will be steadier. Of course, user fatigue and ergonomic design are factors too (as Alan mentioned) but neglecting these effects, the heavier camera will be steadier than a light one with the same moment arm. How is it that I can hold a 400mm Telyt much steadier than a 500mm Reflex-N*****? Their weight is comparable, but the moment arm of the Telyt is much longer: instead of having my hands close together as with the mirror lens, the left hand is at least a foot in front of the shoulder rest, forming a much longer moment arm. Doug Herr Birdman of Sacramento http://ourworld.compuserve.com/homepages/telyt - -------------------------------------------------- Visit the Northwestern Alumni Association portal page at http://www.nualumni.com to get free web-based e-mail and many other exciting features.