Exploring the Itty Bitty: How to Buy a Microscope

By Anthony Rogers
The world of the lilliputian is fascinating. A tiny world within our world; a world bustling, alive with frenzied activity, just beyond the reach of the human eye. Nearly transparent, hyperactive creatures, racing, sliding about their alien environments at breakneck speed, their near-weightless bodies free from the momentum-constrained world of the big. Peering in at them through a tiny circular window, we observe them with intimate closeness; they are completely unaware of us – wholly engrossed in their own world.

Welcome to a drop of water from the neighborhood park pond!

This article aims to give you some direction in choosing an instrument to bring this miniature world to life for your children and students. As long as you know which basic type of microscope is appropriate for your needs, and you know what to avoid, whatever you end up choosing will likely be perfectly adequate, regardless of the more arcane technical details.

The Two Types of Microscopes
There are two basic categories that all optical microscopes fall into: Compound Microscopes and Stereo Microscopes:

Stereo Microscopes are generally of lower magnification (10x to 40x is typical), and more suited for viewing larger objects, such as bugs, rocks, sand, coins, fossils, etc. Specimens require no preparation. You simply place the sample on the stage, ensure adequate lighting, and focus the microscope. This type of microscope is perfect for kids who love bugs and crawly critters – not many things in life will give a little boy more pleasure than viewing a spider 40 times closer! Another important characteristic of Stereo Microscopes is the 3D view they provide, giving a more complete feel for the specimen – very useful for performing dissections, among other things.

Typical stereo microscope

Compound Microscopes generally provide much higher magnification, typically up to 400x or even 1000x. This power has a drawback, however – specimens require preparation – they must be very thin and translucent. If you try to view an ant, for example, all you’ll see is a big, black blob. But the rewards that come with careful slide preparation are fantastic! This is the type of microscope you need if you want to view, among other things, plant cells, skin cells, and of course our little friends - the pond beasties. It’s also important to note that pre-prepared slides are not expensive, so can enjoy the microscope out-of-the-box without any slide preparation. Viewing pond water is also very simple with the use of a concave slide – a slide with a small indentation for holding liquid.

Typical compound microscope (monocular)

What to Avoid
If you see a claim for magnification of 1200x on a little plastic microscope at a local department store or hobby store – don’t waste your money. Even worse than wasting your money, you may end up frustrating any curiosity your children have for using a microscope. To illustrate the problem with these microscopes, think of a movie theater. Visualize a close-up of an actor’s face on the screen. Compared to the face of the person sitting next to you, the actor’s face may appear 20x larger. But visualize carefully – do you see any more detail on the actor’s face than your movie partner’s face? Do you see the fine details of facial pores on the big screen? Can you see intricate detail where the eye-lashes connect to the eyelid? No – you can’t, and the reason is resolution.

Cheap microscopes have very low resolution due to low-quality plastic optics. You will see a bigger version of the same image you’d get with a magnifying glass, but there will be no more detail than with the magnifying glass! With a high quality microscope, you will actually see more with the low 100x setting than you would with the “1200x” setting on a cheaper instrument, even though it won’t appear as large.

A Few Final Things to Look For

• Built in lighting is very important – and there are several methods used to accomplish this. Your first preference should be white LED lighting. LED’s consume extremely little energy and don’t heat up at all. Second on your preference list should fluorescent, then mirror, then incandescent. Mirror and incandescent lightning systems are not all that common any more.
• You want the microscope to have coarse and fine focusing. Particularly with the higher magnifications, focusing can be very finicky, and without a fine focus, you’re likely to get frustrated.
• You want the stage – the part that the slide actually sits on – to be very mechanically secure. There’s nothing quite as annoying as having the specimen disappear because someone bumped the table, just when you finally found something interesting to look at!
• If you’re
  working with a larger group of children, look into purchasing a digital camera attachment. These connect to the top of the microscope, and transmit continuous imagery to a computer or TV.

Now, go find yourself a microscope and a mucky pond, and let the fun begin!