Re: [Leica] 50mm f1.5 Nokton question

["steve lehuray" <icommag@toad.net>]

And to somebody like me who flunked basic algebra this thread makes MEGO 
(Mine Eyes Glaze Over).
Steve
Annapolis

- ----------
>From: "Dan Post" <dpost@triad.rr.com>
>To: <leica-users@mejac.palo-alto.ca.us>
>Subject: Re: [Leica] 50mm f1.5 Nokton question
>Date: Mon, Mar 6, 2000, 3:47 PM
>

> The math is simple; if you have a 50mm lens, and the f ratio is 1.4, then
> the diameter of the aperture (all figures to two significant decimals) is
> 35.71mm, and the radius of the aperture is 17.86mm
>
> For a lens with a 50mm, and an f ratio pf 1.5, the aperture is 33.33mm in
> diameter, and with a 16.67mm radius.
>
> The absolute area of the aperture for both figures is (using 'pi*r*r') is
> therefore:
> 50/1.4 lenses have an aperture area of 1001.60 square millimeters (plus or
> minus 5% would be a range of approx. 50.1mm, i.e.- 951.5-1050.7 square
> millimeters)
> 50/1.5 lenses have an aperture area of 872.58 square millimeters( plus or
> minus 5% of this area would be a range of 43.63 square mm- i.e. 828.95 to
> 916.21 square millimeters.
>
> In absolute terms- if the amount of light hitting the film is a function of
> the aperture size, and the illumination hitting both lenses remain the same,
> then the 1.4 will admit 1001.60/872.58 more light with respect to a 1.5
> lens.... this ratio is 1.15 rounded to 2 significant decimal places.
> Looks like about 15% more light from the 1.4!- a significant increase.
>
> Dan, The Abacus, Post
>
>