Each successive stop is half the area of the previous stop, and therefore
lets half as much light in. We know the area of a circle is
2*pi*r(squared).
A = pi * R1(squared) A/2= pi * R2(squared) known
A = 2 * pi * R2(squared)
multiply by 2
pi * R1(squared) = 2 * pi * R2(squared) Since both
equations are equal to A, the two equations are equal.
R1(squared) = 2 * R2 (squared) Factor out
pi
R1 = square root of 2 * R2 Take
the square root of both sides
R1 / square root of 2 = R2
Divide by root 2, and get the ratio of the stops.
D1 / square root of 2 = D2
Multiply the radii by two, to get the diameter
So, the ratio between the diameters of consecutive stops is the square root
of two. Because in the F/stop formula, the diameter of the opening is in
the denominator, the actual f number increases by a factor of two, as the
diameter decreases by a factor of two.
John
----- Original Message -----
From: "ragowaring" <ragowar...@btinternet.com>
To: <pinhole-discussion@p at ???????>
Sent: Tuesday, October 30, 2001 12:53 PM
Subject: Re: [pinhole-discussion] f stops
> on 30/10/01 3:06 pm, Guillermo at pen...@home.com wrote:
>
> >
> >> ----- Original Message -----
> >> From: "ragowaring" <ragowar...@btinternet.com>
> >
> >>> Anyway, enough of an introduction; could anyone please tell me how to
> >>> calculate the natural progression of f stops doubling exposure from
one
> >>> number to the next, or post a list of these.
> >
> > They follow a geometric progression that make the f/stops increase by a
> > factor of square root of 2
> >
> > Need a more complete explanation? let me know.
> >
> > Guillermo
> >
> >
> >
> >
> > _______________________________________________
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> > Pinhole-Discussion@p at ???????
> > unsubscribe or change your account at
> > http://www.???????/discussion/
>
>
> Wow!, is it really that simple. Of course, it all makes sense now and it
> will be very helpful. Thankyou for your replies. If it is not too much
> trouble a complete explanation would be very welcome Guillermo. Thankyou
> also to Murray for how you calculate the exposure for a given camera; this
> method will help me relate one camera to another; also thanks to Bill
> Erikson.
>
> I too don't know what happened to Philip Arny but he has sent me masses of
> empty messages. I guess if the cat continues on the keyboard this way it
> may come up with one of Shakespear's plays orthe meaning of life,
universe,
> everything.
>
> Alexis
>
>
>
>
>
>
>
>
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