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 microscopes are now available which use a CCD camera to examine a sample and the image is shown directly on a computer screen.

Some of the things you may want to consider:

• 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.
• There may be other features, but the above should be enough for most beginners (and I'm not really expert enough to tell you about them anyway).

The MicroPro (die-cast metal, glass lenses), functions OK and comes with some slides. But if you want it to be more than a toy I would strongly recommend the SCM-200 Junior Microscope, or even better, the P-3A Student Microscope, or the Microscope Digital Kit (MDK, £82) which you can use as a normal microscope, or connect to a computer for viewing and saving digital images. The images are much clearer and they handle cleanly (the focussing on toy microscopes tends to be jittery and too coarse). The MDK also has top illumination as well as bottom illumination, which is very useful for looking at non-transparent specimens (biological specimens are usually thin stained sections). It comes with 3 prepared slides, rocks and honeybee wing. I highly recommend this one if it comes within your budget.

You probably want some slides to look at under the microscope! The ones I mentioned above don't come with any, except the MDK (which also has the attraction of having both top and bottom electric illumination, the others only have bottom illumination). The MDK is well worth the extra money. 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 using bottom illumination only, your samples need to transmit light - i.e. they need to be cut thin enough to let the light through. Otherwise you can of course place a table lamp over the specimen, if the microscope doesn't have top illumination built in.

From time to time we may have some used microscopes for sale. 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.

For more information, please refer to the following links:

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