The Science and Culture of Art - Maui the Kitemaker

Lesson 4 - Up close and personal: What do leaves look like under magnification?

OVERVIEW:

What differences might you see when viewing a leaf with the naked aye and under magnification? Draw them side-by-side and compare. Then let’s take a look at what makes that microscope work.

 

KEY CONCEPTS:

The leaf characteristics visible to the naked eye and with the aid of magnification are very different. Drawing the magnified image as an inset helps students understand how it fits in the “bigger picture”. Students also learn how a microscope works.

 

 

TEACHER BACKGROUND:

We all know that drawing an object can be a great way to heighten a student's skill in observation, but it also helps him or her see and remember details. The scale at which one examines an object will determine the level of detail that it is possible to observe. The level of detail that can be seen will determine just what can be captured in an illustration. A useful exercise is to draw the whole object (in this case a leaf or plant) and then look at a portion of it under a microscope. The small area under the microscope can be drawn as an inset of the larger illustration.

 

If a small portion of the object seen under the microscope is drawn alone, it can be out of context and the viewer may not know what part of the larger whole is shown. Putting the magnified drawing as an inset and indicating the place it represents on the larger specimen helps the viewer to better understand the illustration. A note of the magnification is also useful.

 

Microscopes are wonderful tools that have been around for hundreds of year. Here’s an explanation of how they work, downloaded from “How stuff works” at http://www.howstuffworks.com:

 

How Light Microscopes Work by Craig C. Freudenrich, Ph.D.


Introduction to How Light Microscopes Work

Ever since their invention in the late 1500s, light microscopes have enhanced our knowledge in basic biology, biomedical research, medical diagnostics and materials science. Light microscopes can magnify objects up to 1,000 times, revealing microscopic details. Light-microscopy technology has evolved far beyond the first microscopes of Robert Hooke and Antoni van Leeuwenhoek. Special techniques and optics have been developed to reveal the structures and biochemistry of living cells. Microscopes have even entered the digital age, using charge-coupled devices (CCDs) and digital cameras to capture images. Yet the basic principles of these advanced microscopes are a lot like those of the student microscope you may have used in your first biology class.

 

The Basics

A light microscope works very much like a refracting telescope, but with some minor differences. Let's briefly review how a telescope works.

A telescope must gather large amounts of light from a dim, distant object; therefore, it needs a large objective lens to gather as much light as possible and bring it to a bright focus. Because the objective lens is large, it brings the image of the object to a focus at some distance away, which is why telescopes are much longer than microscopes. The eyepiece of the telescope then magnifies that image as it brings it to your eye.

 

In contrast to a telescope, a microscope must gather light from a tiny area of a thin, well-illuminated specimen that is close-by. So the microscope does not need a large objective lens. Instead, the objective lens of a microscope is small and spherical, which means that it has a much shorter focal length on either side. It brings the image of the object into focus at a short distance within the microscope's tube. The image is then magnified by a second lens, called an ocular lens or eyepiece, as it is brought to your eye.

The other major difference between a telescope and a microscope is that a microscope has a light source and a condenser. The condenser is a lens system that focuses the light from the source onto a tiny, bright spot of the specimen, which is the same area that the objective lens examines.

Also unlike a telescope, which has a fixed objective lens and interchangeable eyepieces, microscopes typically have interchangeable objective lenses and fixed eyepieces. By changing the objective lenses (going from relatively flat, low-magnification objectives to rounder, high-magnification objectives), a microscope can bring increasingly smaller areas into view -- light gathering is not the primary task of a microscope's objective lens, as it is a telescope's.

Make a Simple Microscope

You can make a simple microscope by using magnifying glasses and paper:

  1. Get two magnifying glasses and a sheet of printed paper.

  2. Hold one magnifying glass a short distance above the paper. The image of the print will look a little bit larger.

  3. Place the second magnifying glass between your eye and the first magnifying glass.

  4. Move the second glass up or down until the print comes into sharp focus. You will notice that the print appears larger than it does in the first magnifying glass.