Microscope Use for Children: Exploring the Microscopic World
Exploring a Hidden World
A microscope is a wonderful device that enables children to view a normally invisible world. There is a mysterious and marvellous universe beyond the Earth that attracts the attention and imagination of many people. There is also a fascinating world much closer to us: the microscopic world. A microscope lets us peer into this world. This article reviews desirable features in a home microscope for children. It also describes magnification activities that both children and adults should find interesting.
Microscopes vary widely in magnification power, features, quality, and cost. It's fun and educational to have a microscope in the home, but some care is needed in choosing a suitable instrument. Once a microscope is obtained, slides are required so that objects can be magnified.
Prepared microscope slides obtained from a science supply company are useful. Homemade slides are the most interesting type for children, though. It's fun for them to collect objects and to see what they look like when magnified. Children are especially interested in living specimens, such as creatures in a drop of pond water. My students love examining pond water that contains a rich collection of tiny organisms.
A Magnified View of Pond Water Life
Types of Microscopes
Several kinds of microscopes exist. The type that is used in schools and homes is generally the compound microscope, which is also known as the compound light microscope. A compound microscope uses two lenses to magnify an object—the ocular lens and the objective lens.
A digital microscope may be an attractive option for some people. It sends its images to a computer, where they can be viewed, edited, and saved. It's very important to examine the features of a digital microscope before buying one. The best digital microscopes are compound ones with added features. Some are simply webcams with an ability to magnify an image, however. The final image may or may not be of good quality.
Stereo or Dissection
Stereo or dissection microscopes can also be purchased. These give a low magnification and three dimensional view of an item that is being dissected. A compound microscope is a better purchase for home use because it allows previously invisible objects or details to be seen.
Professional scientists often use electron microscopes as well as compound microscopes. Electron microscopes are far more powerful than light microscopes and produce images with much greater magnifications and resolutions. The microscopes are very large and expensive, however, and can only be afforded by large institutions like universities. In addition, they must be used under special conditions to reach their full potential.
Resolution of a Microscope
"Resolution" of a microscope is the ability to show that what appears to be one point in an image is actually made of two closely positioned points.
Parts of a Compound Microscope
The numbers in the descriptions below refer to the parts of a typical compound microscope, as shown in the photo above.
- Eyepiece or Ocular Lens: used to view a specimen; the lens in the eyepiece magnifies the specimen
- Revolving nosepiece: used to move the desired objective lens into position above the slide
- Objective lens: magnifies the specimen; each objective lens is attached to the nosepiece and has a different magnification
- Coarse adjustment: focuses the image when the low power objective lens is being used
- Fine adjustment: focuses the image when the medium or high power objective lens is being used; the coarse and fine adjustment are sometimes located in different positions on a microscope, but the fine adjustment knob is always smaller in size than the coarse adjustment one
- Stage: a platform on which the specimen is placed; a hole in the stage allows light to reach the specimen
- Light source: an enclosed light that illuminates the specimen
- Condenser lens and diaphragm: the condenser lens concentrates the light on the specimen and the diaphragm lets the user control the amount of light that travels through the specimen
- Mechanical Stage: holds the slide on the stage and contains knobs that can be turned to move the slide; not all microscopes have a mechanical stage
Paramecium in Pond Water
Choosing a Compound Microscope for Home Use
In general, the more features that a microscope has, or the better their quality, the more expensive the microscope. The microscope that's purchased for a home depends not only on its features but also on the family budget and the age of the children in the family.
I've run science labs with elementary as well as high school students. The younger children are very excited to see magnified objects and aren't concerned about how many features a microscope has. As long as the image is sharp enough to see and appreciate and the focusing knobs work smoothly and accurately, they're happy. They do enjoy seeing highly magnified objects, but only if the image is clear and is easy to keep in focus. Older children and teenagers are sometimes more demanding in regards to a microscope's abilities.
It may be tempting to buy the cheapest microscope that's available, but very inexpensive microscopes aren't likely to produce great image quality or last as long as higher quality ones. They are also more likely to develop problems that require microscope adjustments, such as focusing knobs that must be held in place in order for an image to stay sharp.
How to Use a Compound Microscope
Illumination for Home Microscopes
Some microscopes have mirrors instead of light sources. I would never recommend that anyone buy one of these, despite their relatively cheap price. A microscope with its own light source is much more convenient to use and produces a much brighter image.
There are four main types of microscope illumination—LED, halogen, tungsten, and fluorescent. Fluorescent illumination is generally used only in professional research microscopes, but the other types of illumination systems are found in microscopes designed for homes and schools as well as in professional microscopes.
A Magnified View of a Hydra Feeding
Types of Illumination
LED (Light Emitting Diode) illumination is popular in microscopes designed for home use, with good reason. It produces a bright, white light, yet the light housing stays cool. The diodes last for a long time—50,000 to 100,000 hours, depending on the diode. They may never need to be replaced. In addition, the diodes draw low power, so an LED microscope can run on batteries. This means that children can use the microscope anywhere in a home or even outdoors.
Halogen bulbs also produce a bright, white light. However, the light produces heat and may kill living specimens such as pond water creatures if they are viewed for too long. Some halogen bulb microscopes have a rheostat. This is a very useful feature, since it enables the light intensity to be decreased if desired.
Tungsten (incandescent) bulbs are an older type of microscope illumination but are still used. They are not my favourite type of light system for microscopes. The bulb housing gets unpleasantly hot to touch and the heat can kill living organisms. The image may have a yellow cast, although this probably won't bother children. Another problem is that tungsten microscope bulbs don't have a standard form; they come in a wide variety of shapes and sizes. It may not be easy to find replacement bulbs over time. (With good care and a good instrument, a microscope will last for years.)
If someone does buy a microscope that uses tungsten bulbs, I suggest that they buy multiple bulbs while their microscope model is current and keep these bulbs safe for future use. As with any microscope, the instruction manual for the microscope and a record of the part numbers should also be kept in a safe place. The manual should describe how to take out an old bulb and put in a new one.
Chloroplasts Moving in the Cells of Elodea
Calculating the Total Magnification Power of a Microscope
Ocular Lens Magnification
Objective Lens Magnification
Most ocular lenses have a 10X magnification, which means that they magnify a specimen ten times. A common group of objective lenses on a microscope consists of a 4X, a 10X, and a 40X lens. Sometimes a 100X objective lens is included. Some microscopes even have a 200X objective lens.
The magnifications of the ocular lens and the objective lens are multiplied to calculate the total magnification provided by a microscope. For example, the combination of a 10X ocular lens and a 40X objective lens would give a total magnification of 400X.
For children, the 4X, 10X and 40X objective lenses will be the most useful and will create some fascinating images. A 100X objective might be useful, too. Focusing the image at very high power is sometimes tricky, however. The image is also darker than at low power and may not be as sharp. On some microscopes, the 100X objective lens is an oil immersion lens. This type of lens produces a sharper image than a normal 100X one.
Slides and Cover Slips
The specimen to be magnified is placed on a rectangular piece of glass or plastic known as a slide. A square of glass or plastic called a cover slip (or coverslip) is usually placed on top of the specimen.
Oil Immersion Lenses
Oil immersion lenses are designed to be used with a special liquid called immersion oil. A drop of oil is placed on the cover slip that is on top of a specimen and then the objective lens is lowered into the liquid. The oil interface improves the resolution and sharpness of the image.
Immersion oil must never be used with a regular lens. Immersion lenses are sealed to protect them from oil damage; regular lenses aren't. The word "oil", "immersion", or "HI" (homogeneous immersion) is written on lenses that can be used in oil immersion.
Oil must be thoroughly removed from a lens surface after each use with a piece of soft lens paper. This type of paper won't scratch the lens. Additional cleaning may be necessary with liquids intended for the task. Instructions for the cleaning process should come with the microscope. Young children may not have the patience to clean the lens, but enthusiastic older children and teenagers might.
For a keen naturalist or a budding biologist, a microscope with a 100X objective and the extra effort required to get a sharp image at high magnification could be very worthwhile. Oil immersion lenses do work without oil, but the image isn't as sharp as the one that would be formed with the liquid.
Two Features to Consider When Buying a Home Microscope
Monocular or Binocular Head
Monocular microscopes are fine for general use. Binocular microscopes may be more comfortable than monocular microscopes during long periods of viewing. With a bit of practice, though, most people can look through a monocular microscope with one eye while keeping the other eye open. This is a great technique to develop because it reduces eye strain and fatigue.
Binocular microscopes aren't the best choice for a young child. When someone uses a binocular microscope (or a pair of binoculars), the brain combines the images seen by each eye to make one image. This system isn't fully functional in small children.
Coarse and Fine Focusing
An object should be focused at low power first and then at higher power if desired. Modern microscopes usually have "parfocal" lenses. This term means that once an image is focused at low power with the coarse adjustment knob, it will be in focus at higher powers, too. Sometimes small adjustments need to be made, however. It's easier to focus at high power with the fine adjustment than with the coarse adjustment. Some less expensive microscopes have only a coarse adjustment.
The coarse adjustment is larger in size than the fine adjustment. The knobs are often located in different places. Some newer systems have a coaxial system, however. In this system the coarse adjustment and the fine adjustment are on the same axis and the same knob. The coarse adjustment wheel is on the outside of the knob and the fine adjustment is on the inside.
Additional Features to Consider
Using a hand to move a slide in order to look at another part of the specimen works fine at low power. When using a magnification power of 1000X or higher, however, it's very hard for the hands to make the fine movements necessary to reach a specific spot on the slide. A mechanical stage reduces the frustration. This device holds the slide. It has knobs that can be turned to move the slide in small increments.
Disk or Iris Diaphragm
Sometimes the view of a particular specimen is too bright or not bright enough. The disk diaphragm is a circular disk under the stage containing holes of different sizes. The diaphragm can be rotated to put smaller or larger holes into position, thereby controlling the amount of light that reaches the specimen.
How a Paramecium Eats
Preparing Microscope Slides at Home
There are many items that children can collect to look at under a microscope. Examples include sugar, sand, a printed letter on a piece of newspaper, hair, feathers, thread, bits of dead insects, pollen grains, plant parts, moss cells, onion cells, cheek cells, and pond water. The specimen placed on a microscope slide must be thin enough for at least some light to travel through it.
The specimen on a slide is generally covered with a cover slip. This protects the objective lens from contact with the specimen, helps to hold the specimen in place, flattens it, and often improves its appearance under the microscope. A cover slip may not be used in certain situations, such as when the viewer wants to avoid injuring a living and relatively large creature like an insect larva.
Dry and Wet Mounts
If no liquid is added to the specimen, the prepared slide is known as a "dry mount". Adding a drop of liquid to a specimen often produces a clearer image under a microscope. In this case, the prepared slide is called a "wet mount".
To make a wet mount, once the specimen and liquid have been placed on the slide, the cover slip is lowered on to the specimen from a 45 degree angle. This reduces the chance of air bubbles being trapped under the cover slip. Air bubbles obscure anything that's underneath them on the slide.
How to Make a Wet Mount
Looking at Onion Cells Under a Microscope
Some transparent items, such as onion cells, can be seen most clearly when they are stained. The stain is absorbed by the cell parts, especially the nucleus, increasing their visibility.
To obtain cells from an onion, the onion should be broken into layers. The inner curve of each layer is covered with a thin piece of tissue which can be peeled off by fingers or with tweezers. This tissue should be spread out on a slide. A drop of iodine and a cover slip should then be added. After about three minutes, the cells should be nicely stained.
Iodine is readily available in drug stores. Since iodine stains human skin cells as well as onion cells, it might be a good idea for children to wear protective gloves during this exercise.
Since our skin is made of cells, both skin and microscope specimens can be coloured by biological stains. Children should use safe stains under safe conditions.
Examining Cheek Cells
The cells lining the inside of the cheeks are attached very loosely to the cheek and are constantly being shed. If the lining is rubbed (not scraped) with the flat end of a clean toothpick, cheek cells can be collected. The material on the toothpick can be smeared on a slide and a wet mount made with a drop of stain.
The best stain for cheek cells is methylene blue, which can be bought at pet or aquarium stores. A 1% solution is used to stain cells. This stain is very popular and is widely used in schools. It's not considered to be dangerous in small quantities, although it does stain skin and clothes. However, methylene blue is toxic at high concentrations.
In a home situation, an adult should apply the stain to the slide containing a child's cheek cells and the methylene blue bottle should be kept out of the reach of children. Once again, it's a good idea for a child to wear gloves.
Examining their own cheek cells is a very worthwhile activity for children. They are often excited to see cells that have come from their own body.
Prepared slides that are purchased from a store or science supply company can be both interesting and educational. Although my students prefer to make their own slides, they are happy to look at prepared slides when it's either too difficult or impossible to make the equivalent slide in class. The slides are usually stained to emphasis certain parts.
Prepared slides are sold individually and in collections. When buying a collection, it's important to discover what slides are in the collection. Some may not be appropriate for a particular child. For example, there may be too many plant slides compared to animal slides, or vice versa. There may also be some slides that a child or parent may find objectionable, such as ones made from a dog's body.
Microscopic Hunters in Pond Water
Microorganisms in Pond Water
Pond or lake water can be fascinating to examine under a microscope. This is especially true in late spring, summer, and early fall when many pond creatures are active.
Adding a bit of sediment from the bottom of the pond or a few leaves of aquatic plants to a container of pond water can increase the variety of organisms seen. Some pond microorganisms spend their lives attached to a surface instead of swimming freely through the water.
Small organisms that aren't microscopic can also be collected from ponds and examined under a microscope. My classes love to look at mosquito larvae, for example. They are so big that often only part of their body fills the screen at low power, but they are very interesting to observe.
Looking at items under a microscope is an educational, enriching, and entertaining experience for both children and adults. The enjoyment can last through childhood and into adulthood, as it has for me. The amazement of seeing living things and details that are normally invisible never fades.
References and Resources
© 2014 Linda Crampton