On Wed, 19 Sep 2001, Kelvin wrote:
> I just want to be sure I'm calculating this correctly .
>
> I am building a pinhole with a focal length of about 65mm...
> based on the formula below for metric,
>
> that's a pinhole of 0.3mm ... is this correct?
>
> i.e 0.03679 * sq.root of 65
>
> Sorry if I don't quite understand what "SQR" means.
SQR is short for square root. In e-mail people usually specify such
functions in terms of their favorite computer programming language
function. So you might see this as:
d = 0.03679 * sqrt(65)
Another, perhaps even better solution is to use LaTeX
<http://www.latex-project.org/> mathematical notation
<http://www.math.upenn.edu/latex/latex2e_2.html#SEC116>. That would make
this look like:
d = 0.03679 \sqrt{65}
In any case, the trick is in letting people know how you are writing your
equations so they can follow along.
As far as the so-called "correct" equation for the pinhole size to image
plane distance (it isn't really a focal length since a pinhole doesn't
actually focus the light) goes I'd recommend a paper written by a
colleague of mine:
http://www.pinhole.com/resources/articles/Young/index.html
This way you can understand how the equation comes about, and how
different people use different numbers in the expression depending on the
wavelength of light for which the pinhole is optimized.
- Wayde
([EMAIL PROTECTED])
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