Using and Buying a Microscope and Basic Microscopy
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25 April 2010
Here is a short guide to buying and using a Microscope successfully!
Unlike Telescopes and binoculars, some (though not all!) cheap microscopes, even some sold as toys, can have a quite good optical performance and can actually be used at their highest advertised magnification. It is very helpful to have a built in light source, battery or mains operated, especially for higher magnifications, rather than using mirror illumination. Some microscopes can project the light image onto a screen in a darkened room.
You don’t have to spend a large amount to get a usable microscope, knowing what to look for. Children over 8 years old can get a really good introduction to the hobby for a relatively cheap birthday or Christmas present. There are some duds out there in the department stores, so it better to buy from a toyshop or store where they will let you try one out first to see and make sure it has good usable optical quality and a non-flimsy and easy to adjust focusing mechanism! Be sure to try it at high as well as low magnification! For a starter microscope, for beginner hobby use, the "Microscope Lab" microscopes as supplied by Edu Science, Elenco, Discovery Planet, Discovery World and others, in their Microscope Lab Max kit (for just £12- £25), is very good, and is quite usable even at 900x. The image is excellent at lower magnifications, and very good at 900x (or 1200x depending on the model). The 900x model has 8x, 25x, and 50x objective lenses, with a Huygens' Eyepiece, with 12x to 18x zoom, giving magnification ranges of 96x-144x, 300x-450x and 600x-900x. There is a colour filter and iris diaphragm wheel, with a battery lit bulb and a mirror. The kit contain most of what’s needed to start with. This includes a Petri dish, safety scalpel, slides and covers (though the covers are plastic), collecting vials, and some basic reagents/ colouring agent. You can easily add test tubes and culture dishes for reagents and cultures. The microscope supplied is a reasonably sophisticated and capable scientific instrument, especially considering its extremely reasonable price!
If you can spend a little more, or for regular hobby use, for £60 upwards you can get a very solidly made modern microscope with a widefield eyepiece and up to 400x magnification. It is possible to buy a 20x widefield eyepice for £15 - £20 which will extend the magnification to 800x, with excellent eminently usable image quality at this magnification. These, if you can afford them, are a revelation at highest magnifications, compared to cheaper or older microscopes, producing large bright very detailed images, often with a larger eye relief (increased distance of the pupil from the eyepiece). They are a must for Advanced level or Undergraduate biological or biochemical studies.
Hand magnifiers eg jeweller’s loupe type often have the magnification quoted (unlike optical microscopes!) as an area magnification where the 30x actually means just over 5x size magnification. These can give (especially if illuminated) surprisingly good results for viewing stamps, banknotes, coins and jewellery or 'field' objects.
Low power Simple microscopes’ (usually plastic with glass lenses) have a low power eyepiece and objective for viewing larger items at lower magnifications (up to about 80x), where the specimen can be manipulated while viewing, or more powerful. A modest 20x - 40x illuminated magnifier can be bought for well under £10!
‘Compound’ microscopes with higher power eyepieces and particularly higher power objective lens systems, need properly prepared slides. It is very good to have a simplemicroscope and a compound microscope !!!! Especially as compound microscopes often start at 100x magnification upwards! If you have a compound microscope with 40x or 80x, you may be able to use an LED torch shone above solid objects to view them. Highest power (1000x upwards) quality compound microscopes have oil-immersion objectives.
The top end is binocular microscopes which use a prism and double eyepieces to view a 2D image. These can be expensive, though an excellent quality instrument of this sort can be bought for about £130.
Digital eyepieces can be bought for approximately £35 upwards to capture images from compound microscopes on a computer.
There are also Stereo (Binocular) microscopes with eg 40 - 80x magnification that give stunning 3D views of larger specimens, though you might have to be very lucky to get one of these for under £50. Do try car boot sales for these!
CCD (non-optical) USB microscopes display the image on-screen via a computer monitor. These can be very good and often fairly reasonable price-wise (£40 upwards), and quite often (but not always!) use lower magnifications. They operate independently on their own.
If you have a scanner, try scanning a portion of a pencil line at a high resolution and viewing the resulting image at a higher magnification! The scanner technique will also work well for a range of specimens, eg cloth etc.
Optical magnification is the product of the eyepiece power x the objective power, so a 10x eyepiece and 4x objective would give a 40x magnification.
For general studies, 80x is adequate. Cell studies and some bacteria may need 400x - 800x magnification. Above 1000x the image is only larger, having the same detail resolution as for 1000x, being an optical limitation, even with the best optics. Better optics will however show more detail and have a brighter larger image up to 1000x or so, and beyond. Oil immersion optics will also produce better results above 900x magnification. For studying viruses (which are very very small indeed), up to 2000x magnification and special techniques are needed, usually beyond the scope of amateur microscopy.
Incidentally, regarding magnification, many smaller medical labs only use up to 400x, though some of the bigger facilities, with rarer conditions to investigate, may use 1000x - 1500x, so some of the cheaper microscopes that provide 800x maximum are actually very powerful and capable instruments! The higher the magnification, the more difficult it is to focus; light adequately and find the part of the slide to view. Very high magnifications for optical microscopes have an extremely small field of view. They also have very small eye relief, making viewing much more difficult, needing the eye very close to the eyepiece. Generally, compound microscopes have a set of different power objectives on a rotatable turret, to let lower powers and hence lower magnifications to be used while finding different parts of specimens by moving the slide. They may also have interchangeable eyepieces for further adjustment of the magnification.
Always start by moving the lens system viewed from the side of the microscope. Then view through the eyepiece and adjust the focus finely up or down until clearly in focus.
Focusing is much trickier and more difficult to achieve with higher powers, and the objective lens is very close indeed to the slide. It is necessary to re-focus the microscope each time the magnification or specimen slide is changed. As the depth of field in focus is very small, it may be necessary to re-focus when moving the specimen slide. Focusing and lighting are the two most important factors apart from slide preparation. You can't take too much trouble and care in getting these right, and both often need a very fine light touch to get just right!
Be very careful when focusing at higher powers, not to hit/ break the slide cover (or slide!), as it also possible to then damage or break the objective lens. If you have a safety stop, use this!
Some specimens are ‘light shy’ and need a means to adjust the brightness of the illuminating lamp. This can be tricky to achieve with cheaper microscopes. Mirror light illumination system can be adjusted for brightness by moving the mirror. Battery systems will need some kind of filter or ‘iris’ system and variable transformers (or eg dimmer switches) or more complex iris systems are needed with mains lighting systems. Bulbs are easier to adjust, as modern LCD’s and halogen spotlights are very bright; though it may be possible to partly dim halogen spotlights, though reducing their life-span. Microscopes with a movable condenser lens may need the condenser position carefully adjusted for best lighting effect.
A very useful tip for specimen viewing is that even different parts of the same slide nearly always benefit from adjusting the light level, each time the slide is moved. Always re-centre the part of the specimen you wish to view under a higher magnification! Never use direct sunlight on a microscope mirror for illumination, as a very important safety measure. Always set the objective lens approximately in position by side-ways viewing, before looking through the eyepiece and focusing.
One very useful accessory is a polarising filter, which helps cut down reflections depending on the angle it is turned around to. Double polarising filters are good at setting the amount of light used to illuminate the specimen. By varying the rotation of the two filters, fine adjustment to the illumination is possible. By putting one filter behind the specimen and one in front (at a lower magnification!) stress patterns can be observed eg in clear plastics!
Sets of pre-prepared slides are available and are usually of a very high quality. Some can be imported from the USA at eg 100 slides for £40 including postage. Some UK prepared sets are very expensive by comparison. Secondhand shops or car boot sales can often provide real bargains here, though the quality of the slides can be variable. EBay often has these secondhand pre-prepared slides listed. Catalogues of the larger sets can provide good ideas for specimens to prepare for yourself! There are also some very reasonably priced beginner sets - you may have to search hard to find these though, as they only have a very few (sometimes just one!) supplier(s).
Collecting Specimens - can be a lot of fun!
Spring, Summer and Autumn can be the best time to be out and about. It is vital to avoid falling into water, however shallow, or anticipated shallow.
Small screw-top plastic containers of various sizes are excellent for collecting specimens. Pollen can be tapped or shaken into the smallest containers. Item like leaves and flowers can be put into small containers with some water already in them to keep them fresh when they are collected.
Insects as specimens can be put into small containers that have been pre-sprayed with an insecticide (Adult only or supervised). If you catch wasps and similar or ants, be sure they are dead before handling. Wasp stings can still be venomous after the wasp has died. Please don't catch and kill bees except perhaps later in the year. They are needed for pollenating flowers. Some butterflies and moths are rare and very beautiful species. There are plenty of more common varieties to catch as specimens. Also please don't trample over wild flowers, some are getting much rarer these days!
Do be aware that cultures eg moulds, bacteria made in limited oxygen conditions can often be harmful (ie poisonous) and a possible serious risk in from breathing dust, without a breathing mask. Moulds (though not bacteria) grown in the open air are far safer to handle!
Small hand magnifiers are useful to use ‘in the field’, and some have a chamber to hold specimens for easy viewing and to hold live specimens temporarily!
Small insects and insect parts, pond wildlife(eg algae and parasites in pond water), seeds, pollen, plants and trees, flower petals, mosses and lichens, minerals and crystals, soil, moulds and fungi, bird feathers, small cellular organisms, fish parts, natural and artificial fibres, biological specimens (eg skin, inside cheek scrapings, hair, tissue, blood) and suchlike all make very good slide specimens if prepared properly.
Handle glass, especially cover slips, very carefully. Clean up after breakages with a vacuum cleaner and/ or wet paper towel. If skin is cut, wash wounds out throughly and bandage or use dressings. If there is any possibly of glass fragments getting in eyes or being left in wounds, seek immediate medical assistance.
Most of the time, you can just prepare slides to view over a short time period rather than preserving the specimens!
Mineral water or distilled water is better to make wet mounts for slides as tap water can kill small organisms because of its chlorine (and fluorine, if present) content. Many specimens are transparent and benefit greatly from staining with coloured dyes. More powerful optical compound microscopes use oil immersion objectives, where a drop of fine special oil is used to fill the usual air gap between the objective lens and the specimen slide. This gives a clearer image at magnifications from 1000x. More expensive microscopes also have a fine tuning mechanism for higher (essential for 1000x upwards) magnifications, and a mechanical slide stage to move the specimen very small amounts horizontally right to left and up or down at these magnifications.
Cheap Indian inks, in a range of colours when diluted can be used to stain home made specimen slides. To prepare a home slide, a fine scalpel or safety razor blade is used. A lit stand magnifier will help enormously, or use at least +4.00 diopter glasses to see clearly, using a cutting board, and be especially careful not to slice your fingers,. Generally, the finer the thinness of the specimen slice, the better. It may take several (or many!) attempts to get a really good specimen eg from a slice of a leaf or a plant stem. A really sharp blade helps, but do mind your fingers! If necessary, the specimen is then stained, and mounted on a slide with a thin glass cover slip attached around its edges lowered one side first to avoid air bubbles, and ‘fixed’ in place around the edges using gum arabic or a very little white PVA glue. For liquid specimens, again staining will usually help greatly, and a very small amount is pipetted into a special slide with a small dish curved into it, and again a cover slip is added. It helps very greatly to completely avoid fingerprints on the slide or cover disk, unless you wish to view fingerprints!!!! I have made a really excellent slides from the cross-section of a plant stem in this way, it can just take some practice! A needle and fine tweezers are essential for handling small specimen slices. An eye dropper pipette is very useful for putting one small drop of a liquid or solution onto a slide. You can also drop some melted candle wax onto the specimen and when set, this makes cutting a fine slice much easier. If this is done in the head of a nut protruding partly from a bolt, the nut can be unscrewed very finely and a scalpel used to cut a layer (eg of plant material) maybe just one cell thick - ideal as a specimen for the microscope! Cover slips or cover glasses are very thin square (or round) pieces of glass (or plastic) that are placed over a water drop on the slide. Because of surface tension, a water drop sits as a thick dome. With a cover slip in place, the drop is flattened out by capillary attraction allowing focusing with high power very close to the specimen. The cover glass also confines the specimen to a single plane and thereby reduces the amount of focusing necessary. Finally, the cover glass protects the objective lens from immersion into the water drop and provides permanent protection for a mounted slide. With an oil immersion objective, it allows a drop of specially refractive oil to be held between the objective lens and the cover glass, and keeping oil away from the specimen. Some thicker samples need pieces of cover glass to build up a thicker channel before the cover glass top layer is added. With fast moving aquatic specimens, either add some cotton or cotton wool strands to confine their movement, or add a very small drop of alcohol or diluted washing up liquid to slow them down, or some very dilute bleach. A commercial go slow preparation can be bought, which slows them down for ten minutes or so very well.
For semi-permanent preservation, put into some hot Vodka (Adults only. Heat in a saucer over hot water ONLY. DON’T overheat or use a direct heat source, it will flame! And never leave unattended!), leave to cool and stand eg overnight or for 24 hours, remove from the alcohol and fix on the slide, once the alcohol has evaporated, either with some hairspray or gum Arabic. Alternatively, put some 40% Vodka in the freezer (not 37% proof, this freezes!) and freeze dry the specimen (Place into the very cold vodka retrieve with tweezers after after a minute or so) and and mount as before with hairspray or gum Arabic, before adding a cover slip. This won’t work for some specimens where rarely, ice crystal damage can occur while freezing. Children need parental supervision in preparing slides. If fingers are cut while handling eg soil samples or some biological specimens (of animal or human origin), medical advice should urgently be sought.
Maintenance consists of cleaning lenses outside surfaces, with a clean soft cloth, and only if absolutely necessary, neat alcohol, or lens cleaning fluid. If needed, a tiny drop of oil or very small amount of white or copper grease can be very carefully put on the focusing mechanism if it is easily accessible. That’s it, nothing else! And never try to dismantle the microscope, ever!
Protect the microscope from dust when not in use and it will give many, many years of faithful service!! If kept in a warmer dry location, problems with mould and fungal growth will also be avoided. Please don’t drop or force mechanisms! Modern microscopes are precision instruments that have been developed to a high degree of mechanical and optical perfection over very many years.
Slides may need careful wiping to remove fingerprints and fatty deposits.
While the microscope presents an image, a great part of the skill is in observing and interpreting what is seen. A lot of this comes down to practical experience, theoretical knowledge and sometimes a great deal of actual practice, and particularly, a great deal of patience and very careful observation!
Do read books and internet articles, eg identifying the main types of parasites in pond or aquarium water is a lot easier if you have some idea what you are looking for! Microscopy can be a very entertaining and enjoyable hobby ! (and eg for aquarium keepers an essential aid and diagnostic tool).
You may be able to take digital photographs as well with a digital camera through the microscope, but focusing the camera may partly be trial and error!
You can also read articles on the Internet telling you about the techniques that are used by professionals but which are beyond the scope of amateur investigations! The highest magnifications (10,000x -25,000x) are with electron microscopes but these are highly professional and inordinately very very expensive instruments, taking up a large amount of space and needing highly trained operators!
You may be able to take digital photographs as well through the microscope with a digital camera, but focusing the camera may partly be trial and error!
You can be amazed at what you can see even in a quality budget microscope. As an example of the extent of the microscopic world, there are more living, tiny organisms in a tablespoon of soil (though you may only be lucky enough to see some of the larger ones!) than there are people on Earth! The detail in many microscope specimens is truly remarkable.
You will get the best results, whatever microscope you use, by focusing very carefully, and re-focusing, after moving slides or specimens, and adjusting the lighting carefully with new specimens or after moving slides!
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