..... Stumper Index
Stumper #22.
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How Good Is Your Science KQ?

[i.e. your Knowledge Quotient]


- Let's Focus! -

"Focus, n., 1 Optics. The point at which rays converge after reflection by a concave mirror or refraction by a convex lens, also known as a real focus. The point from which rays appear to diverge after reflection by a convex mirror or refraction by a concave lens is known as a virtual focus." (Webster's 1913)

Focus is a technical term, a physics concept involved, as the definition above reminds us, in "optics". Focus is what we need in order to see well, and what a photographer generally tries to achieve in most of his or her photographs. Focusing the image is only part of the process of seeing or of taking a photograph - but it is the focus of this stumper.

Focusing your eyes is accomplished by rapidly changing the shape of the flexible lens in each eye so that light rays entering the pupil converge on the retina and whatever is being looked at is immediately in focus. The images produced are fleeting and cannot be recaptured.

Focusing a camera is accomplished by moving the (solid) camera lens back and forth to change its distance from the film; and in non-automatic cameras, often by choosing an appropriate lens for a particular need. The image produced is recorded on the film and can be preserved for posterity.

People have been creating well focused photographic images since the mid 1800s. Some of these are well known photographers. Ansel Adams (1902-1984) created black and white images of Yosemite and the Southwest that exhibit a dramatic clarity of focus and contrast. Edward Weston (1886 -1958) achieved a reputation for using sharp focus revealing minute, sensuous detail. Dr. Harold E. Edgerton (1903 - 1990) the legendary MIT scientist who pioneered high-speed, stop-motion photography photographed a .30 caliber bullet passing through an apple in perfect focus!

So, focus can be an important aspect of a photograph ...
The stumper question:
When I took a picture of a mirror in which the reflection showed me taking the photograph, the result was a mirror in perfect focus and my reflection distinctly blurred. This was not the result I had anticipated. I am not a great photographer but I did focus carefully on the frame of the mirror. Why was my reflection not in focus?

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