Physics Photo of the Week
November
30, 2007
Simple Lens
A simple
magnifying lens inverts the image of a "distant" object. Hold a
simple magnifying lens at arm's length and look at a distant object
through it. You see an inverted image of the distant object
through the lens. The inverted image is called a "real"
image.
That is because if a screen (paper, frosted tape, or frosted glass)
were placed at the appropriate position between the lens and the
viewer, the inverted image would be projected onto the screen.
Without the frosted screen, the viewer sees the image of the inverted
object as if the object were originating at the image location between
the lens and the viewer.
Focusing
the camera to show this inverted image of the distant object is a bit
tricky. The auto focus camera "wants" to focus on the
distant objects. In the image at right, the auto-focus was used
to focus on the distant spruce tree. The image location was
between the lens and the camera - so close to the camera that the image
of the spruce tree is way out of focus. To photograph the main
picture above, care was taken to focus the camera on the lens itself,
not the distant object. That is a reasonable compromise - both
the distant object and the close-up inverted image are in reasonable
focus. The poor focus was not discovered until the image was
processed the following day. Consequently, when I went out to
re-do the image, the sky was overcast, and the lack of color renders
the overall image not as attractive.
A similar inverted real image exists in all photography. The lens
projects a real inverted image onto the film - or solid state sensor in
a digital camera. Our eyes also work on the same principle.
The cornea and lens of our eyes make up the "simple" lens and the
retina provides the "film" - or bioelectronic sensor. The image
in our eyes is real and inverted.
A future Physics Photo of the Week will feature a virtual ("unreal?")
image produced by a simple lens.
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to dcollins@warren-wilson.edu.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
