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Parabolic dish antenna & confusion




Greetings!

In addition to my other work I figured I'd use ferret for a hobby, in visualizing
the parabolic dish antenna I need to find the focus for. I did the following:

        set window/size=1/aspect=1
        plot/i=0:100 0.00935 * i^2

Now I thought the focal point distance would equal to the Y of the point where
the first derivative is 1 (and vertical rays reflect to horizontal). However, the
"visual D=1 point" where the pixels are diagonal =) is somewhat off the value
I got with good old pen&paper.
Is this aspect=1 thing crooked or is it my brain? Or ferret assuming that pixels
are not square?

 -Jonni Lehtiranta

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