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Another Advantage of Binos?

Started by Milt, 01/30/2003 08:32PM
Posted 01/30/2003 08:32PM Opening Post
Hello All,

Another reason to like binos for astronomy occurred to me in the wee hours this morning: It seems to me that all other things being equal, binos should show less color than single objective spotters or other refractors. My reasoning is that when the light gathering gets split between two objectives totalling the same area as one, the lenses don't have to be as fast to produce the same FOV.

Take 16x70's, for example, which have the same light gathering area as a single 100mm objective. Let's say their focal length is 300mm (I'm guesstimating since the f.l. is seldom given for fixed-mag binoculars). Dividing 300 by 70 yields f/4.3, already a fast lens. Now try to maintain the same focal length with a single 100mm objective, and you would need an f/3 lens! More bending equals more color, right? Or am I missing something here?

Thinking too much,
Milt
Posted 01/31/2003 12:31PM #1
Milton, you make me grin. I've gotta like somebody that stays up late thinking of reasons to like binoculars for astronomy :-)

I don't know about optical theory, but I do know that higher power binoculars generally show lots more color than lower power bins. That's to be expected. For instance, both the Fujinon FMT-SX 16x70's and the Miyauchi 20x77's show considerably more color than less powerful binoculars. In the Fuji line, the 10x70's show virtually no color, while the 16x70's show purple on really bright objects if you look for it. With the Miyauchi Exceeds, one hardly has to look for it. It's there. Likewise, many of the various 20x80s out there really show more color than even cheap ST80 scopes at 20x.

I think a large part of it has to do with the quality of the objective and the quality of the prism. I keep waiting for somebody to come out with an affordable 80mm or 100mm binocular that features a triplet objective.

Mike Swaim