Re: Focal length by using sun (and trees)

On Tue, 23 Oct 2007 17:34:37 +0100, winke <winke@xxxxxxxxxxxxxxxxx>
wrote:

On Mon 22 Oct 2007 09:09:50, Tom Hubin <thubin@xxxxxxxxxxxxx> wrote:
snip




Tom, I am the OP and what you write is useful for me to know because it
helps me understand some of the other variables involved which may have
affected my readings.

Winke
It's very simple for a tree 10 meters away. The lens will be
struggling with a builtin DIvergence = -.1d = 1/10m.
The focal power of the lens is reduced by .1d.
The *net convergence* out of the lens is the *sum*:
Diopters out = Nd - .1d
To find the right diopters from your focal distance, just add .1d to
1/FD.
John Polasek
.

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