What fools a lot of people, Mark, is that the view
through the camera does not "look" twice as bright
when we open up one stop. I,ve had a difficult time
explaining this to people who insist the screen only
looks twice as bright when you open up two stops. They
believe their eyes before they accept the math. John
--- "Mark A. Thalman" <mthalman@xxxxxxxxxxxxx> wrote:
> Tom Scales wrote:
>
> > I'm confused. I thought one stop was the square
> root of 2 brighter (about
> > 1.4) and TWO stops was twice as bright.
> >
> > Am I missing something?
>
> You just have it backwards.
>
> One Stop is twice as bright. To double the area of
> a circle you multiply
> the diameter by the square root of two. The
> increase in brightness is a
> power of two. A two f-stop increase is 4 times the
> light (2*2). A three
> f-stop increase is 8 (2*2*2) times the light, etc...
> To achieve a one
> f-stop difference with a starting aperture of 1.0
> the diameter needs to be
> multiplied by 1.4 (the square root of two). To
> achieve the f-stop you
> divide the diameter of the diaphragm by the focal
> length.
>
> Clear as mud now?
>
> --
> Mark Thalman, markt@xxxxxxxxxxxx
> f u cn rd ths thn u cn gt gd jb prgrmmng cmptrs
>
>
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