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How to Buy the Right Microscope

Intro» Construction» Optics» Light» Focus» Components» Used» Conclusion

Chapter 5. Additional Microscope Components

Many of the components discussed below are "sub-stage" mechanisms that help manipulate the light just before it passes through the specimen. If you see a photo of a microscope with little or nothing visible below the stage (where the slide goes), it is likely that the scope has the simpler or cheaper version of the component.

Diaphragm

A diaphragm is a simple device between the light and the slide that controls the amount of light that passes through the object being viewed. There are two kinds of diaphragms generally available today. Most microscopes have one type or the other built in.

Microscope Disk DiaphragmDisk Type Diaphragm

First is the disk type, it is the simplest, the least expensive to manufacture, and as a result, is the most frequently seen in student scopes. The disk is mounted beneath the stage, and usually has six holes in it, each one progressively smaller. The largest aperture is wide open, while the smallest is very small.

To adjust the light on the scope, the disk is turned…a larger hole is used for more light, and a smaller hole for less light. This works fine, but what do you do if you need a setting just between two of the given holes? My experience tells me there are times that you'll wish you had an intermediate setting.

I love looking at protozoa in pond water (I'm easily entertained), and one of the most needed tools during such times is the diaphragm. These microscopic creatures easily become "washed out" by too much light (i.e., contrast is lost).

At these times you'll reach to adjust the diaphragm…and you'll want one that gives you just about infinite adjustability.

An Iris Diaphragm provides that flexibility.

Iris Diaphragm

Microscope Iris Diaphragm An iris diaphragm is constructed of a number of interconnected "leaves" that, when adjusted with a simple lever, open and close much like the pupil in your eye.

The beauty of such a device on a microscope is that it gives you almost an infinite number of settings. You are not limited to six or eight like you would be with the disk diaphragm.

Additionally, the iris diaphragm is much easier to adjust while using the scope. You can watch the changes in lighting take place while you peer through the lens. With the disk diaphragm, the lens goes black between settings…leaving you in the dark!

A good microscope is an investment in learning and adventure. An iris diaphragm is a good investment that will pay for itself over and again in many situations. If an ad you are looking at does not specify "iris" diaphragm, it probably has a disk type. The iris diaphragm is superior, and it will allow you to see things that simply cannot be seen with the disk diaphragm.

Using the iris in my Premium I can easily see the internal organelles of the single-celled protozoa I find in a nearby swamp. (Oh joy!)

GreatScopes offers student microscopes with both types of diaphragms, each is documented on its webpage.

Condenser

Just about every microscope has a condenser. This is the small glass lens you'll see built into or under the stage whose purpose is to gather and focus light.

Light passes into the bottom side of this lens, and is focused, that is, it is condensed, into a cone of light. Since light travels in waves or particles, normally there would be fewer of those waves/particles passing through your subject at high magnifications.

A condenser directs more of those particles through your subject and into the lenses, so that you have enough light to see.

A sub-stage, movable condenser comes into play in situations where very high magnifications are used (say 1000x and more), where light starts getting extremely scarce.

You see, the location of the focal plane in relation to the light can vary, based on slide and/or subject thickness. Since the condenser is movable, it can be focused right on the focal plane yielding precise lighting. The "Abbe" (pronounced just like Dear "Abby") is the most common type.

At the risk of getting a little technical here, we need to talk a little bit about the "numerical aperture", or NA of the condenser. Your microscope manufacturer will take care of all the technical details of this for you, but if you are adding a lens (such as a 100x oil objective) to a microscope that you already own, the NA of the condenser must be greater than or equal to the NA of the lens that you are adding.

If you will be operating at 400x and below, you will do just fine with a fixed (not movable) condenser, most of which have a NA of .65. However, if you will be working at 1000x, a NA of 1.25 is common on such a lens, in which case a 1.25 NA movable/focusable condenser is required.

Again, when you buy a microscope, the manufacturer will take care of all this, but this will explain why some microscopes do not support 1000x magnification.

Filter Holder

A simple filter holder and filters is built into with many microscopes. These can be useful in providing enhanced contrast and light color correction. In some cases, colored filters can be a simple substitute for staining, which would kill live specimens.

Mechanical stage

Many of us are used to moving the slide around on the stage with our fingers. In a lot of situations, that is just fine. However, there is a gadget that is made for smooth, accurate movement of the slide. It is called a Mechanical Stage.

A Mechanical Stage is a nice convenience, usually optional on student compound microscopes, and usually standard equipment on medical and lab scopes.

A mechanical stage has two knobs. One moves the slide up and back, while the other moves the slide from left to right. These controls move the slide slowly and precisely, giving you exacting control of slide position.

If you are serious about looking at things under higher magnification, you will need a mechanical stage (as well as the fine focus discussed above). A nudge of the slide while using 1000x magnification will take the subject completely out of view. Some folks wouldn't be without one at 400x - it just depends upon how nimble your fingers are!

Mechanical stages can be added to most student scopes by means of a thumbscrew, which holds it in place. Some scopes are not pre-drilled to accept a mechanical stage.

In most cases, you will not need a mechanical stage, but it can be a nice option to have. (While the mounting holes are somewhat standard industry-wide, you are advised to obtain your mechanical stage from the same manufacturer as your microscope to guarantee proper fit.)

Built-in mechanical stages are standard on professional microscopes. Our Premium offers it as an option.

All of GreatScopes Student Series microscopes are pre-drilled for mechanical stages. We offer mechanical stages as an option with each of these scopes. Our professional microscopes have mechanical stages as standard equipment.

The next chapter, Should I consider a used microscope?, will help you determine if a used scope is what you want.

Go to the next chapter: SHOULD I CONSIDER A USED MICROSCOPE?

Intro» Construction» Optics» Light» Focus» Components» Used» Conclusion

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