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posted: 8/12/2014 12:03 PM

How lenses bend and shape light to help us see

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  • Dr. Keith Brown uses an optical microscope to examine the salt crystal seen on the monitor. The optical microscope uses a system of lenses and light to magnify very tiny things so they can be inspected closely.

      Dr. Keith Brown uses an optical microscope to examine the salt crystal seen on the monitor. The optical microscope uses a system of lenses and light to magnify very tiny things so they can be inspected closely.
    Courtesy of Maria Cabezas.

 

You wanted to know

A young patron at the Grayslake Public Library District asked: "How do magnifying glasses make things bigger?"

Convex or curved, dome-shaped glass called a lens, bulging in the middle and thinner at the edges, can magnify an object.

A similar effect can happen using a glass of water -- things you look at through the glass appear larger. Lenses also can be shaped to make objects appear closer -- like a side mirror on a car.

Ancient Greeks and Egyptians knew this, but used curved lenses for a different purpose. Concentration of the sun's rays when directed through the lens can create fire.

By the year 1,000, Arab scientist Alhazan studied light as it moved through lenses, mirrors and the atmosphere and developed the foundations for the science of ophthalmology and optics.

"Rays of light are affected in two ways when they enter into materials like glass, they slow down and they change direction," Louie Klein, Warren High School physics teacher, said in explaining how glass captures light to create a tool to enlarge objects.

"In glass, light rays will slow to approximately two-thirds their speed in the air, and they will also change direction, refract, depending on the angle they strike the glass at. By the time the light rays reach the lenses in our eyes, their trajectories have changed, which tricks your brain into thinking that they came from a different point."

Directing light through lenses is the concept behind how eyeglasses, contacts, telescopes, cameras and microscopes work.

A microscope is the best tool to see objects that are as small as one micron (.001 millimeter) so you can see things as tiny as parts of cells.

But if you want to see something really, really small, a regular microscope or magnifying lens can't help you. Scientists developed an atomic force microscope, which uses a mechanical probe to create a 3-D image of minute objects. In some cases they identify individual atoms.

At its International Institute for Nanotechnology, Evanston's Northwestern University has an atomic force microscope used to magnify parts of cells. Keith Brown, postdoctoral fellow, is studying ways to mend position cells or proteins using really, really small scale tools.

"We're good at making small electronics, but not good at making things in the medical area that are very small," Brown said. "Our research is focused around hopes to miniaturize biological or medical tools to be as small as possible and reasonably priced so medical tools are much more accessible."

How tiny are the objects Brown works with?

"Small is relative. A hair is small, being about a tenth of a millimeter, or 100 microns in thickness. A single cell is around 10 times smaller. You can't see a single cell with your eyes."

The materials he works with are much smaller still, about 50 atoms wide.

"We are learning how to reliably make a great diversity of really small structures, and might be able to use them for studying genetic disease and individualized personal medicines," Brown said.

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