Thanks. Why didn't I think of that? I'm still curious about whether there's
a formula for determining focal length from sphere diameter. ----- Original
Message -----
From: Kosinski Family <zin...@telenet.net>
To: <pinhole-discussion@p at ???????>
Sent: Friday, January 12, 2001 5:05 PM
Subject: Re: [pinhole-discussion] optics question


> WE writes:
> "Can anyone give me a simple formula for the focal length of a
> spherical lens, or whatever the terms are, to get a sharp image?"
>
> The easiest thing to do is measure it directly!
> Hold the sphere up in front of a white card and focus the sun on the card.
> The focal length is the distance from the card to the center of the
sphere.
> Jim K
>
>
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