Make it larger than life

8th September 1995 at 01:00
Roger Frost casts his eye over a selection of microscopes for classroom use.

A microscope is one of the great constants of science equipment. Given that no microchip will replace all that precision ironmongery, it is a rare blessing of today that you can buy something which, pupils permitting, will last for years.

But whether you are buying one or two for a primary school, or a set for everyone in an advanced biology class the choice is baffling. Microscopes range from Pounds 50 to Pounds 5,000, their features overlap and there is an array of options.

So with the help of Phil Punyer, chief technician at City and East London College, we set up numerous systems, to look for the features that help make a short list. For example, you'd want a wide field of vision so that the circular "field" almost fills the eye-piece instead of giving you tunnel vision. You would want the image to be not just sharp, but sharp from its centre to the edge. And then, other things being equal, you would want a "nice" image which, like choosing a television, is subjective. These then are some features you really can't assess without seeing the product.

Junior schools will not be so fussed the need is to keep the price in perspective with how much you use it. To see the finer things in life, you either spend lots or use a Bioviewer (Pounds 8.45 with slide sets extra NES Arnold), a simple slide viewer that "cons" the children into thinking they're looking down a microscope. It's almost a toy but it is "appropriate technology" used by thousands of schools and colleges.

A real microscope, where you look through a glass slide is still worth having the Motic 3A (Pounds 59 Philip Harris) will do for looking at hair, paper and things that children are curious about. Middle schools might like the easier focusing on the Motic 3AF (Pounds 79 Hogg). With both of these microscopes, the eyepiece can be adjusted towards you others are fixed at an angle, which is fine, or vertically, which is a pain.

Many microscopes use a concave mirror to gather light from a window but for GCSE work you would want a microscope lamp. However, Phil Punyer finds these too troublesome and had even upgraded a set of mirror-type microscopes with built-in light fittings. He says "For GCSE you would need a class set of microscope lamps which take time to set up and clear away. The cost of a built-in light source is much the same anyway."

We started looking for a microscope which would be good for GCSE work and we found something slightly better in the Motic 100 FL (Pounds 211 Philip Harris). This too was a good compromise for advanced level, where you'd insist on having one-per-student.

This Motic had an in-built light source, a wide field of vision and a simple condenser a lens system which improves the resolution and lets you adjust the light, as you'd need to for different specimens. It had focusing controls which were to hand near the bottom of the stand. There were separate course and fine focusing controls we found these more predictable to use. There was a focusing-stop to prevent students from crunching slides. It also had some very practical extras like a pointer in the eye-piece that helps you to direct students to a particular feature. More importantly there was a captive eyepiece and captive slide clips as students like to make souvenirs out of these.

At advanced level, you will occasionally want to pump up the magnification and use a x100 oil-immersion objective. These give you an inside view of a blood cell, but just a reasonable picture of a Staph, the skin or pimple bug, which still shows as a dot. You have to put a drop of oil between the specimen and the lens, and they also demand a special "high aperture" condenser, called an Abbe condenser. Costs for these systems go from Pounds 350 for a Motic 100 FLA to the Leica BF200 (Pounds 494 Griffin) and the Swift M3203 (Pounds 891 Hogg).

You can spend more binocular microscopes are more comfortable to use, and a mechanical stage allows you to steer around a slide and to return to a set position, instead of pushing the slide with fingers. Then there's that enigmatic "build quality" but for all this you need to magnify your budget.

NES Arnold Scientific, Ludlow Hill West, West Bridgford, Nottingham NG2 6HD. Tel: 0115 945 2200 Hogg Laboratory Supplies, Sloane Street, Birmingham B1 3BW. Tel 0121 233 1972.

Philip Harris, Lynn Lane, Shenstone, Lichfield, Staffordshire WS14 0EE. Tel: 01543 480077.

Griffin George, Bishop Meadow Road, Loughborough, Leics LE11 0RG. Tel: 01509 233344.

Other sources of microscopes: Commotion, Unit 11, Tannery Road, Tonbridge, Kent, TN9 1RF. Tel: 01732 773399.

Irwin-Desman, 294 Purley Way, Croydon CR9 4QL. Tel: 0181 686 6441 Hope Education, Orb Mill, Huddersfield Road, Oldham, Lancs OL4 2ST. Tel: 0161 633 6611

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