Posted by Bruce A Clarke on October 13, 2001 at 08:08:14 from 203.149.1.101:
In Reply to: Re: Telescopes posted by Mike Field on October 13, 2001 at 01:43:31:
With reference to Mike's comment about binoculars, the 7x50 also gives an indication of how useful the binoculars are as "night glasses". If you divide the magnification into the lens diameter, eg 50 divided by 7 then the answer is about 7. This means that the lens has the capability to concentrate the amount of available light by 7x less the loss through the lenses which is a loss of about half the concentrated light. This means that 7x50 binoculars effectively give about 3.5 to 4.0 times effective concentration of the available light. 12x50's would only supply about 2x the available light which added to the "shake" factor makes them fairly useless as "night glasses".