Buying a Microscope

and how to use it

An Introduction to Microscopy


The choice of an instrument for amateur use depends partly on the available money, partly on the intended use.

New or second hand? There are several producers of good new instruments. The famous brands often have at the lower end of their product line an affordable instrument. And there are also good instruments available of minor brands, mostly produced in Japan, in a price range that is within the reach of an amateur. Second hand instruments of a famous brand are often available. Sometimes it is possible to buy excellent instruments for a very reasonable price. Although the model may not look very modern, you must realize that the optics is the most important part , and good objectives and microscopes do not become obsolete. If you are new in the field, ask the advice of an experienced amateur or member of a microscope club. When you are completely new in the field, consider to buy a stereo microscope first. A stereo microscope gives you the possibility to look at whole insects, small flowers, small fossils at magnifications from 10-60x, without any preparation. (do not confuse it with a binocular microscope) Such a stereo microscope is sufficient for a lot of purposes. And later on, when you feel the need for higher magnifications, a stereo microscope is very valuable for preparing and sorting of specimens. The worst you can do is to buy a toy microscope in a warehouse. These boxes, complete with scalpels, a pair of scissors and some chemicals look very impressive but the optics are made of plastic and give terrible vision! It will spoil what could have been the start of a great hobby.

What type of lenses? There are two important things to consider. Modern achromatic objectives are of excellent quality. Buying very expensive apochromats or planapochromats makes only sense for very demanding colour photography or for the resolution of very fine details. For most purposes, achromats are completely sufficient. If available, fluorites are excellent and cheaper then apo¹s. The objectives most used are 10x, 20x and 40x. Beginners are often thinking that the highest magnification is best!

What to consider before you buy a microscope? For photography the microscope must have the possibility of Köhler illumination, a built-in illumination makes work a lot easier. If you can buy a new instrument, a second consideration is if the microscope has the possibility for extensions, is it built modular. Does it have the possibility to add a binocular or trinoculair tube if you start with a monocular instrument; is it possible to add later on a phase contrast set, dark field or a better condenser?

How to use the condenser? Beginners often use the condenser (the part of the microscope that directs the light through the sample) in a wrong manner. They regulate the intensity of the light by closing or opening the condenser diaphragm or by adjusting the height of the condenser. The intensity of the light must be adapted to a convenient level by means of the voltage on the lamp. Closing the condenser diaphragm diminishes the resolution of the microscope, always open the diaphragm as wide as possible . To achieve sufficient contrast you have to close it a bit, a good rule of thumb is to open the condenser diaphragm for two thirds of the maximum opening. A second rule of thumb is to put the condenser in the highest position against the object glass, that is often almost the best situation.

How do I get a good illumination? For photography you need an even illumination. This is obtained by centring your lamp, and projecting the lamp spiral sharp in the plane of the condenser diaphragm. You can easily control this with a piece of paper in the plane of the condenser. Adjust the height of the condenser until you have the diaphragm in focus and adjust the condenser until the diaphragm is neatly centred. Do not use a ground glass filter.

What types of illuminations are possible? Some of the most used types are illustrated in Illumination and contrast techniques for the light microscope.

How do I prepare an object for examination? When you want to look at a certain subject under the light microscope you have to put it on a object glass and cover it with a coverslip. Because the strong magnification of the microscope gives a very shallow depth of field it is necessary to have a very flat sample. The object has to be submerged in water or other fluid (For making permanent slides there are all kinds of substances available). When you are preparing a slide, do not use too much water. The cover glass must not float above the object. A small drop suffices. The trick is to get the sample as flat as possible. When you examine pond organisms it is often necessary, in order to keep your specimens alive and not press them to death by the cover glass, to lift the cover glass a bit. By applying a little bit of vaseline under the four corners of the coverslip you prevent the larger specimens from being crushed. By pressing the coverslip carefully you can reach the ideal depth for the slide.


Back to An Introduction to Microscopy

More tips can be found in the article Choosing and buying a microscope by Dave Walker

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