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Proper focus??



 
 
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Old November 3rd 03, 01:47 AM
bigc
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Default Proper focus??

Hi Gurus,

I need a help to compute the focus of a lens.

I want to make sure my camera can see a 10 feet by 10 feet table
from about 9 to 12 feet away. So what is the proper focus of
the lens that I should choose?

Current, I have a 8.5mm focus lens, it can see 42in height and
31in width from 72in away. So I just assume everything is linear,
then: if I want to see from 9 feet, the proper focus is L. We have

8.5/L=D/9,
where
D/6=10/(31/12)

Then L=3.3 mm

Is it correct? Please help me to check.
Thanks.

Regards,
Zhen
 




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