You won't get closer

Cliff Porter examines a range of microscopes to suit all ages

Microscopes are made up of four basic components: a light source; a stage to hold the specimen; a system of lenses to generate the image and a mechanism to focus it. Basic microscopes will have a mirror underneath the stage to direct sunlight through the specimen. External lamps provide a more reliable source of light and microscopes with an integral lamp, built in to the base, generally provide the best illumination. Advanced microscopes have halogen lamps and a condenser to channel the light through the specimen. A drawback of this arrangement is that image quality will be lost if it is incorrectly adjusted. On more expensive microscopes there should also be a brightness control for the lamp, to consistently achieve the best image.

Specimens are first mounted onto a glass slide which is held onto the viewing stage by clips. On rudimentary microscopes, the slide is manoeuvred on the stage by being pushed manually. More desirable is a mechanical stage which has a screw mechanism to smoothly and accurately position the slide, but these are usually found only on expensive models.

The heart of any microscope is its optics. The objective lens, just above the stage, gathers light from the specimen and projects it to the eyepiece, which forms the final image. The final magnification is the product of both lenses. So, a X40 ("times 40") objective coupled with a X10 eyepiece lens would give an overall magnification of X400. Monocular microscopes have one eyepiece, whereas more advanced binocular microscopes have two and the image is viewed with both eyes. A sharp image is achieved by moving the objective lens into position above the specimen using the focus mechanism. This must be smooth and robust as it is the part of the microscope that takes most of the normal wear and tear. On more expensive microscopes, look for a separate "fine focus" knob which is essential when using higher magnifications.

When buying a microscope, first consider the type of use it will get. Viewing objects such as whole insects or flowers needs a microscope that can accommodate such large specimens. These are sometimes called stereomicroscopes and have magnifications around X20 or X40.

They are excellent for seeing fine detail while maintaining an overall view of the specimen. For greater magnifications, thin sections or prepared specimens are mounted onto a glass slide. The hairs on an insect leg are visible from X40, large plant cells will be seen well at X100 and details such as cell nuclei will require magnifications of X400. To view bacteria, a specialised oil immersion lens will be necessary. Producing magnifications of X1000, they are difficult and messy to use so are only advisable in a school laboratory if advanced microscopy is required. As with any piece of equipment, choosing a microscope is a balancing act between quality, price and its ability to survive the everyday rough and tumble of the classroom. The most expensive microscope is useless with scratched lenses covered in greasy fingerprints and a focus mechanism that has a mind of its own.

QUANTUM BIG SCREEN MICROSCOPE. Learning Resources. Key stages 1 and 2. Price: pound;45.95 + VAT. Tel: 01553 762276. www.learningresources.co.uk. Magnifications: X10, X20 and X40

FIRST IMPRESSIONS

Looking like a television screen attached to amicroscope, the Quantum Big Screen could be the answer to your dreams; one microscope viewed by a group of students. Think again. It may have a bigviewing area but doesn't make the most of it.

IMAGE QUALITY

The Big Screen is just not up to the job. Measuring 125mm x 175mm, the screen offers a large viewing area, but the size of the visible image is much smaller. The three-volt bulb, powered by two "C-type" batteries, is not powerful enough to generate a decent image although using the optional mains adapter may improve this.

EASE OF USE

Magnification is changed by rotating the lenses into position and an adjuster knob allows the image to be focused. The plastic construction means both of these actions are jerky and a little difficult to performaccurately. Likewise, the position of the stage and the proximity of the lenses make it a little awkward to manipulate the slide.

VERDICT

It could be what you are looking for, but try before you buy.

QUANTUM ALPHASCOPE. Learning Resources. Key stage 2. Price: pound;29.95 + VAT. Tel: 01553 762276. www.learningresources.co.uk. Magnifications: X10, X30 and X50

FIRST IMPRESSIONS

Made out of plastic and looking like a "proper" microscope, the Quantum Alphascope comes with a range of accessories, including slides and tweezers. Especially useful are paper slides that contain a plastic, fold-over window to capture the specimen. They are available from a range of suppliers and are much better for young students than glass slides which have sharp edges and break easily.

IMAGE QUALITY

Two "AA" batteries power bulbs that illuminate the specimen either from above, for viewing flat materials such as paper or fabrics, or below when using prepared slides. Viewing prepared slides produces reasonable images and detail at all magnifications.

EASE OF USE

Objective lenses are rotated to change magnification and, with a little care, "click" into their correct location. The plastic constructioncontributes to the focus being stiff and jerky, which proves a littleawkward, but generally the results are quite reasonable for a microscope at this price.

VERDICT

A solid and cost-effective primary school starter microscope.

ILLUMINATED POCKET MICROSCOPE + CONVERTING STAND. TTS Group. Key stage 1 and 2. Price: pound;9.95 + VAT. Tel: 0800 318686. www.tts-group.co.uk. Magnifications: X50

FIRST IMPRESSIONS

An inexpensive pocket microscope with a fixed X50 magnification. IMAGE QUALITY

An integral three-volt bulb, powered by two "AA" batteries, illuminates the specimens well. Used without the base, the crude focus rarely needs adjusting.

EASE OF USE

Focusing is by means of a thumbwheel which is a little stiff to turn. The Lumagny has a removable stage to view prepared slides, but the position of the clips makes it difficult to manoeuvre specimens into the position and, in this mode, it is not very effective. However, remove it from the base for use like a powerful magnifying glass and surprisingly good results can be achieved. Operated in this way, the Lumagny brings into sharp view the tangled fibres of a seat cover and the dot-matrix nature ofnewspaper photographs.

VERDICT

Once you remove the base it is easy to use and would be ideal for enthusiastic littlescientists exploringthe classroom.

MOTIC MICROSCOPE. BrightMinds. Key stage 2 and above. Price: pound;79 including VAT. Tel: 0870 44 22 144. www.brightminds.co.uk. Magnifications: X20

FIRST IMPRESSIONS

Microscopes of this type generally do not have a mirror or integral light source and use available light to illuminate a specimen which sits on the base. They are designed for viewing large objects, such as invertebrates or mineral samples, at relatively low magnifications. Their objective lens has a wide field of view and they are excellent for seeing the fine detail of an object while still keeping the perspective of its overall structure.

IMAGE QUALITY

Crisp images from an inexpensive microscope. The Monoscope has a fixed X20 magnification which sounds a little limiting, but is ideal for bringing to life features such as the facets of an insect's compound eye or the valleys and hills of a fingerprint.

EASE OF USE

The focus mechanism is positive and easy to use, which means the Monoscope would be a good addition to any primary science class. However, its construction and quality mean that it would not be out of place in a secondary setting.

VERDICT

The Monoscope is a piece of "real" science equipment at a very affordable price. It has good optics whichproduce clear, sharp images.

MICRONPRO MICROSCOPE. Commotion Group. Key stage 2 and above. Price: pound;99 + VAT. Tel: 01732 773399. www.commotiongroup.com. Magnifications: X10, X80 and X160

FIRST IMPRESSIONS

An innovative design has produced a very good microscope packed into a robust, plastic body. Measuring only 103mm in diameter by 27mm thick and weighing just 225g, the Micron is a pocket-sized model containing optics which give good results at both low and high magnifications. Its small size and plastic case makes safe storage easy.

IMAGE QUALITY

Magnification is changed by moving a slider control on the underside of the microscope and a thumbwheel adjusts the focus. Obtaining a really sharp image when viewing slides at high power proved a little awkward, but the X160 magnification was perfectly adequate for viewing onion epidermis cells.

EASE OF USE

A built-in light source, powered by two AA batteries, is held in an arm that is swung out to view prepared slides or retracted to illuminatesurfaces. Slides are held to the stage by a magnetic collar, which makes moving slides a little awkward, but it does have the advantage that flat surfaces can be viewed without the obstruction of clips. The eyepiece is housed along the side of the microscope and can be detached to provide a X10 magnifying lens for viewing larger specimens.

VERDICT

Swing-out arm could be prone to damage. Changing lenses requires considerable re-adjustment to refocus the specimen, but this is a small price to pay for its portability.

STE NUFFIELD MONOCULAR MICROSCOPE. Griffin and George. Key stage 4 and above. Price: pound;133 + VAT. Tel: 01509 233344. www.griffinandgeorge.co.uk. Magnifications: X40, X100 and X400

FIRST IMPRESSIONS

This is the classic secondary school microscope. A solid cast metal frame and base make it very strong and well able to resist the everyday knocks of the school science lab. Supplied in its own wooden box, the Nuffield also has an edge when in comes to surviving life in a busy prep room.

IMAGE QUALITY

Good quality lenses give clear and crisp images although illumination on the model tested was by means of a mirror and adjustable sub-stage condenser. An optional light source that clips into place underneath the manual stage can be added for about pound;50. On its highest power, the detail of nuclei and nerve cells in a prepared slide of the retina were clear and sharp.

EASE OF USE

Coarse and fine focus controls are solid and there is a particularly useful focus stop screw which is easily adjusted to prevent over-zealous students crashing lenses into the specimen. Moving the slide around on the stage can be a little awkward, but mechanical stages are generally found only on much more expensive microscopes.

VERDICT

The Nuffield microscope is easy to use, solid and has good optics. For AS and A2 classes it is hard to beat.

Pyser-SGI XEC-M10AQ. Griffin and George. ASA2 and above. Price: pound;198 + VAT. Tel: 01509 233344. www.griffinandgeorge.co.uk. Magnifications: X40, X100 and X400

FIRST IMPRESSIONS

This monocular microscope has a modern look and carries good quality optics. It would not be out of place in an undergraduate laboratory and has been produced with emphasis on sophistication rather than battle-hardened toughness. It is best confined to use with post-16 students who should be able to handle it with care.

IMAGE QUALITY

The M10AQ has an integral halogen light source in the base and a sub-stage condenser which allows the user to get good, even illumination. On a microscope of this standard it would be useful to have an intensity control so that the light could be adjusted when switching from one objective to another, but images produced at all magnifications were excellent.

EASE OF USE

The manual stage makes positioning slides a little tricky, but upgrading to the equivalent model with a mechanical stage could be quite expensive.

VERDICT

Overall, the M10AQ has the look and feel of a good quality undergraduate microscope. Treat it well and it will reward with excellent images.

ADVANCED CAMERA 3 DIGITAL. Philip Harris. Key stage 4 and above. Price: pound;795 + VAT. Tel: 0845 1204520. www.philipharris.co.uk. Magnifications: X40, X100, X400 + optional X100 oil immersion

FIRST IMPRESSIONS

The Advanced Camera 3 microscope contains an integrated camera which allows output to a computer or television. The microscope is supplied with software that is fairly intuitive to use. Connection is straightforward via a computer's USB port. Additional outputs enable images to be viewed directly on a television screen or recorded onto video. Digital images can be stored, labels added and areas highlighted.

IMAGE QUALITY

A halogen lamp provides good, even illumination that passes through a sub-stage condenser. The light has an intensity control which gains the best performance from the high-quality lenses. As would be expected from a microscope of this standard, the images formed are excellent when viewed from the integral digital camera or through the monocular eyepiece.

EASE OF USE

The construction is solid and, if treated properly, should be long-lasting. A mechanical stage allows specimens to be moved accurately into place and objective lenses locate into their positions with an unmistakable "click". Coarse and fine-focus controls are smooth, which means that themicroscope is easy to use with low and high power lenses.

VERDICT

Pricey but high-quality digital imaging. The Camera 3 gives very good results but is best reserved for teacher demonstrations or use by trusted students.

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