I'm sometimes asked to recommend a microscope for a smart child or adult - i.e. something better than a toy, but not professional. The cheapest microscopes, intended for children, tend to be barely adequate. They are usually plastic, including the lenses, and the images are poor. As with telescopes - and most things in life - price is generally an indicator of quality.

The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest and simplest of the microscopes. Digital optical microscopes are now available which use a CCD camera to examine a sample and the image is transmitted via USB and shown directly on a computer screen.

Good children's microscopes are really hard to find. Some might say, impossible. The lenses are usually plastic and poor quality. The highest magnifications are almost useless. Getting a good focus can be hard. The supplied slides are boring. And so on.

We find the MicroPro (die-cast metal, glass lenses), functions OK and comes with some slides.

Or consider getting a digital hand-held microscope, which is great for studying rocks, leaves, bugs, the back of your hand, or bits of your head, the computer monitor screen (see the individual colours in the pixels), or even your own eye!

The 'classical' microscope requires that specimens be cut into very thin slices and mounted on slides.
Children's toy microscope sets usually come with some prepared slides, though they tend to be as poor as the microscope. If you're going to look at random stuff from the kitchen or garden (and why not?) then be aware that if using bottom illumination only, your samples need to transmit light - i.e. they need to be cut thin enough to let the light through.

This might tax the enthusiasm of some children, so the afore-mentioned digital hand-held microscope avoids that - as does the stereoscopic microscope. Although the magnification is only 20x, this is adequate for getting up close & personal with bugs, etc.

Now if you want to view plant cells or bacteria, a magnification of a few hundred would be better. Consider the
P3-A Student Microscope or the SCM-200 Junior Microscope.

Let's compare them: The P3-A

1. has slightly better build quality
2. can be angled (not just 45°), which may be easier to work with
3. mirror is attached to the upright not the base, makes it easier to angle to the light
4. mirror is double-sided, flat one side, concave the other, so more illumination choice
5. has a pointer in the eyepiece (not that I personally find that very useful)

The SCM-200 has a stage condenser (lens in the substage to focus the illumination from below), and a Huyghenian flatfield. Overall, the P3-A has the advantage, for a few pounds more.

From time to time we may have some
used or vintage microscope. These generally offer the best value for money, if you don't mind that the microscope isn't pristine; the optics should usually be as good as the day it was new, barring perhaps a little dust that can be wiped away.

Microscope Basics

• The top lens that you peer through is called the eyepiece; the bottom lens near the specimen is called the objective. Often there will be 3 (or so) objectives of different magnifications (e.g. 4, 10, 40) that can be rotated into place. You may also get more than one eyepiece; you can take one out and replace it with another.
• Total magnification is found by multiplying the eyepiece and objective magnifications, e.g. if the eyepiece has a magnification of 10x, and the objective (that is in place under the tube) has a magnification of 40, then the total magnification is 400x. Except for professional use, you don't need more than this.
• Monocular, binocular, stereo. Monocular refers to the 'usual' kind of microscope, that has one tube to look down. Binocular has two tubes that share one objective lens. Stereo microscopes have two tubes with two objectives, so that you get the stereo effect.
• Focussing is done by means of 'rack and pinion' to raise or lower the tube, with a wheel both left and right of the tube. This is 'coarse' focussing, there may also be a couple of smaller knobs for 'fine' focussing.
• There is a 'stage' on which a glass slide with specimen is placed. The stage may offer a condensor, which is a special lens to even out the illumination; and a rotating disc with different sized holes, to vary the amount of light that goes through (like the aperture on a camera).
• Illumination: top and/or bottom. There is usually a mirror under the stage, which can be swivelled around to reflect light up through the condensor and specimen. The mirror is usually two-sided, one side is flat, the other is concave, to focus the light onto the specimen and provide brighter illumination. Instead of the mirror you might get electric illumination, by bulb or LED. There may also be above-stage illumination, good for thicker samples that don't transmit much light.

For more information, please refer to the following links:

• Choosing and buying a microscope
• The Beginner's Microscope?