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-----Original Message-----Case (1)
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf
Of Anthony Lapinski
Sent: Tuesday, May 23, 2006 3:49 PM
To: tap-l@lists.ncsu.edu; tap-l@lists.ncsu.edu;
phys-l@carnot.physics.buffalo.edu
Subject: [Phys-l] half lens
If you cut a plastic lens in half (through the diameter), you
can still form real images. Compared to the original (full)
lens, the images are the same size (same focal length), but
appear half as bright.
So I asked my students a follow-up lab question: If you put
black tape over half a camera lens (the old SLR type), how
would the images be affected? Obviously, they would be intact
but half as bright, no matter which half of the lens was
covered. But a few students, who are also in a photography
class, said you would only see half the object/scene. They do
this as a project using a "photo divider," which attaches to
the front of the lens and can rotate. So one can do double
exposures of half a scene at a time. Wow!
I had never heard of this before. And it seems to contradict
the half lens demo I did in class. Can someone tell me how
these camera attachments work? Do the objects have to be
"very close" to the camera?