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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12569
Loc: Cumberland, R I , USA42N71.4W
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Terrestrial Viewing
02/05/04 06:23 AM
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Do the critical specs/features to look for when buying large binoculars change when the dominant usage will be distant terrestrial viewing, or do the same factors apply as for astronomical observing?
Large binoculars for distant terrestrial objects
...you mentioned looking across considerable expanses of land & water. In the daytime, frequently there is considerable heating or cooling of the air (what the meteorologists call heating-degree or cooling-degree minutes). This in turn causes thermal activity, which causes the kind of shimmering "funhouse effect" to the image that you see in the movies when a scene is filmed in the desert...the higher the magnification, the more pronounced it is. I currently have 4 hi-end binos and a premium scope and do a lot of birding by local lakes. I find that very seldom can I use the really hi-power eyepieces on the scope and often even the stronger binos don't work as well as the lower powered ones when there is several degrees difference between the air temp and that of the water surface, or between air temp at ground level and just up a few meters. Air has to very stable to have good seeing conditions if you're talking about looking at something much over 2-3 miles away and seeing it to best advantage. I can only use the highest power eyepiece on my scope (48x) very seldom and get the kind of image it's capable of producing...usually the lowest pwr ep (24x) will give a cleaner, more usable view with just as much detail, just a smaller image. This is one of the problems of terrestrial viewing vs cosmological....when stargazing you're looking thru much less dense air which isnt as susceptible to thermal currents
additional posts will be added
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member#21
Edited by EdZ (02/05/04 06:35 AM)
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