Archived posting to the Leica Users Group, 2007/01/18
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 09:22 PM 1/18/2007, Don Dory wrote: >Eric, >Traditionally birding binoculars need to be at the long end of what you can >hold to your eyes for minutes at a time with out eye fatigue due to hand >shake. For most people that is in the 8X area. People with steady hands >will go up to 8X and those with a coffee habit might have to go down to 6X. >Next, you want the brightest pair you can carry around your neck without >breaking it. Birds tend to hang out in nice safe dark places so you need >the best light gathering you can get. So, traditionally birders use >something like an 8X40 pair or even something like a 7X50. Divide the >numbers and the closer you get to 7 the better for you; the human eye can >open up to about 7mm so if the cone of light coming out of the binoculars >is >7mm or more then you are getting all that your eye can see. Don Your comment is a valid one, but the 7mm figure for the average size of the dark-adapted eye only works for teenagers. By the time you hit twenty, your maximum size starts getting less and less and by the time you are 60, it's probably around 4mm. Anything beyond this is wasted light, so middle-aged folks can get as much benefit from, say, a pair of 6x,30mm glasses as from anything larger. This topic comes up all the time on the Royal Astronomical Society of Canada list and we do have some dedicated binocular stargazers there! Marc msmall@aya.yale.edu Cha robh b?s fir gun ghr?s fir!