Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!snell From: snell@utzoo.UUCP ( ) Newsgroups: rec.birds Subject: More on Binos: Light Gathering Ability--a Simple Formula. Message-ID: <9084@utzoo.UUCP> Date: Wed, 9-Dec-87 17:37:58 EST Article-I.D.: utzoo.9084 Posted: Wed Dec 9 17:37:58 1987 Date-Received: Wed, 9-Dec-87 17:37:58 EST Organization: U of Toronto Zoology Lines: 36 Should have mentioned this in previous posting. (Also, no, I don't own rubberized binoculars. I think they are foolish and unnecessary for the reasons I stated). Lovely Light. The more your binos take in, the better. The trade off is that good light gathering plus magnification equals weight. A simple formula will help you easily determine how good a set of binoculars will be at this essential task. Weight and optical quality are separate considerations. Light Gathering Ability = Objective Size / Magnification Thus Light Gathering of 12 X 30's = 2.5 (I've seen such at K-Mart). " " " 10 X 30's = 3 (I've seen these at a K-Mart too). " " " 9 X 40's = 4.44 " " " 7 X 35's = 5 " " " 8 X 40's = 5 " " " 10 X 50's = 5 " " " 7 X 50's = 7.14 " " " 3 X 30's = 10 (These are typical opera glasses) " " " 7 X 80's = 11.43 (I saw such a pair in a Marine Museum in Iceland. They were beautiful... and huge) The Light Gathering Ability of a `zoom' lense varies depending on the magnification. Obviously Leitz 9 X 40's do not come out as winners in the Light Gathering War, but the optics are so much superior that they more than compensate. __ Name: Richard Snell Mail: Dept. Zoology, Univ. Toronto Toronto, Ontario, Canada M5S 1A1 UUCP: {allegra,decvax,ihnp4,linus,pyramid,yetti,utai}!utzoo!snell BITNET: utzoo!snell@utoronto.bitnet