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Old Oct 16th 2013, 11:23 AM   #1
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Camera obscura calculating optics

A camera with a pinhole has a focal length 10 cm. The height of a tree is 5 meters. How large is the picture of a tree on the inside surface if the tree is 14 meters from the camera?

Is my calculation correct?
Code:
f = 10; //cm
Z = 14 * 100 //cm
X = 0;
Y = 500;
x = -f * (X / Z);
y = -f * (Y / Z);
y + x // Size of a picture
And why do we don't use camera obscura any more? What is the benefit of camera's with lenses?
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Old Oct 17th 2013, 11:07 AM   #2
MBW
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Location: Bedford, England
Posts: 668
Too Little Light

I don't know about your calculations...

However the key to a pin-hole working is its small size,
This small size restricts the amount of light, giving a very faint image.
A lens collects the light for its image from a much larger area,
thus the image generated is much brighter.

Particularly when "wet" film was used and exposures were measured in seconds,
the extra brightness afforded by a lens was invaluable.

With modern super-efficient charge coupled devices,
a pin hole perhaps starts to become practical.
Indeed if you look at the tiny size of modern camera phone lenses,
the lens is more to reduce the focal length than anything else.
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