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Microscope Troubleshooting Tips Buying Microscopes
How to Use a Compound Microscope Evaluating a Microscope
Microscope Magnification Specifications Barlow Lens Explained
The Microscope Parts and Specifications History of the Microscope
Barlow Lens Explained
A Barlow lens is a diverging lens that alters the focal length of a microscope and, therefore, the magnification power and field of view. They also alter the working distance between the objective lens and the specimen, which is a critical variable for many applications such as PCB soldering and inspection.

A Barlow attaches to the bottom of the objective lens on a stereo (low power) microscope when there is a need for either more or less of one of the following variables:

¡öWorking space
¡öField of View
The most common type of Barlow lens is the Reducing Barlow. A Reducing Barlow reduces the magnification power of the microscope, but has the advantage of increasing the field of view and the working distance between the objective and the specimen. Reducing Barlows are typically 0.3x, 0.5x and 0.75x although other powers are available.

As an example, a 0.5x Barlow lens will halve the magnification power of the microscope, but it will double the size of the field of view. It will also increase the working distance between the objective and the specimen.

By the same token, a 2.0x Barlow will double the magnification and halve the field of view of a microscope. In other words, each different power Barlow has a proportionate effect on magnification and a direct inverse proportional effect on the field of view and working distance.
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Buying Microscopes

We start with the premise that choosing a microscope should be an enjoyable process!

That said, there are a number of variables that go into selecting a microscope system. The process can be a little daunting. Moreover, there is a bewildering range of quality - from cheap plastic microscopes to the most expensive German and Japanese brands.

This article, therefore, provides sensible advice to assist budding microscopists to make a more educated decision.

We recommend that you refer to the Glossary of Microscope Terms when reading this guide.

Before we start, you should know that everything in this article refers to light microscopes; that is a microscope that includes a built-in light source. There are other types of microscopes, such as electron or ultraviolet, but they are significantly more expensive and typically, used in commercial or scientific applications


Microscopes are configured to suit different applications. It is important to ensure that you purchase a microscope that is well-suited to your application. There are three basic things you need to know:

First, a light microscope has two sources of magnification. The primary source is via the objective lens. The secondary source is via the eyepiece lens. Total magnification is achieved by multiplying the (magnification) power of the objective lens by that of the eyepiece lens.

For example: Standard eyepieces have a power of 10x. When using a 100x objective lens, the total magnification would be 1,000x.

Second, and perhaps most important of all, do not fall into the trap of being attracted by high levels of magnification. The vast majority of the world¡¯s light microscope applications require magnification levels of less than 60x!

Third, you need to know whether you need a compound or stereo microscope.


Microscopes fall into two basic categories: Compound or Stereo, often referred to as high power or low power, respectively.

Compound Microscope
You will need a compound microscope if you are viewing "smaller" specimens such as blood samples, bacteria, pond scum, water organisms, etc. The reason is that such specimens require higher powers of magnification in order to see the detail. For this reason, a compound microscope is also known as a high power microscope. Typically, a compound microscope has 3-5 objective lenses that range from 4x-100x. Assuming 10x eyepieces and 100x objective, the total magnification would be 1,000 times. Compound microscopes are also integrated systems in the sense that the microscope body and base form an integrated unit.

When considering a compound microscope, you will also need to decide on whether you want a monocular, binocular or trinocular microscope. That is to say, a microscope with one, two eyepieces or one with two eyepieces and a third, trinocular port.

There are four basic variables in this decision:

1. Magnification: Monocular microscopes work efficiently for up to 1000X total magnification. For higher magnification levels, a binocular microscope is required.

2. Comfort: Most people find binocular microscopes more ergonomic and easier to use than monocular. Young children, on the other hand, find monocular easier to use.

3. Price: While the price ranges overlap, typically a monocular microscope is the least expensive type of microscope with trinocular being the most expensive.

4. Application: Most monocular microscopes do not include a mechanical stage, which is useful for more sophisticated applications. Most binocular microscopes do include a mechanical stage. A trinocular microscope is typically used when a third (trinocular) port is required for microphotography.

Stereo Microscope
You will need a stereo microscope to view more substantial specimens such as insects, bugs, leaves, rocks, gems, etc.

Typically, such specimens require lower power, magnification ranges from 6.5x-45x. Hence they are also known as low power microscopes. By definition, a stereo microscope has at least two eyepieces (binocular), and provides a three-dimensional image of the specimen. They are available in one of two configurations: dual power or zoom. In the first instance, the microscope has two magnification options, for example 20x-40x. In a zoom microscope, there is a continuous zoom range from the lowest power to the highest power. For example, from 6.5x to 45x.

As with compound microscopes, stereo microscopes also come in a trinocular configuration for photographic purposes. Stereo microscopes can be integrated microscopes or, increasingly often, are modular in the sense that different stereo microscope bodies can be assembled with different bases.

For most individuals, an integrated system is appropriate. Some users require specialist microscope bases such as boom stands for applications such as PCB inspection or engraving applications.


Now that you have decided on the type of microscope you need, there are several further variables to consider, most important of which is quality. Quality particularly applies to construction, lens and illumination. We will consider each of them.

a). Quality of construction
Most people believe that higher price equates to higher quality. This is partially true, but overly simplistic in the same way that it would be in referring to a car. As with a car, the finest light microscopes in the world tend to be extremely expensive. There are several well-known German and Japanese microscope brands that fall into this category. However, as with Ferrari cars, most people cannot afford them and do not need that level of refinement.

By the same token, there are a large number of low priced and low quality microscopes that range from plastic toys to cheaply made imports. Most of these are made of inferior quality materials, have minimal optical quality and are likely to break quickly. The vehicular equivalent might have been the Yugo! The danger of buying such microscopes is easily avoided by buying from a reputable microscope vendor.

In our opinion, there is now a healthy selection of fine quality microscopes that have excellent optics, but without the high price tags associated with well-known brands. In other words, like cars, many microscopes are now made that will achieve the same as the high-end brands, but without being "fully-loaded" or the brand cachet, so to speak! Our own Omano microscopes fit into this category. They are designed with an excellent engine (high quality optics), offer a comfortable drive (ergonomic design) and do not break down (reliable everyday use). Perhaps Omano is the Toyota of the microscope world!

Implicit in such microscopes are design elements such as solid metal alloys, high quality prisms rather than mirrors and iris diaphragms not disk type diaphragms, among others.

That said, in our experience, we recommend caution in purchasing any full-size, light microscope that is priced less than the following:

b). Optical Quality
Optical quality is largely determined by the quality of the objective lenses and, to a secondary degree, by the quality of the eyepieces. The standard for good, quality objective lenses is an achromatic lens. An achromatic lens is one that corrects for the fact that different colors refract through a curved, glass lens at different angles. In "color correcting," the microscope produces a significantly, enhanced, "flatter" specimen image of the specimen than would otherwise be obtained.

However, while achromatic objectives will satisfy most microscopists, some sophisticated users need a better quality objective that produces even flatter images of the specimen with less aberrations than achromatic lenses. These microscopists will require either semi-plan or plan objectives. Plan objectives, essentially, are "perfect lenses" and are usually required for sophisticated biological research¡­..and are double the price of achromatic objectives.

Finally, it is useful to ensure that the objectives are DIN compatible. While DIN (Deutsch Industrie Norm) is not a measure of quality, DIN objectives are useful since they are interchangeable from one DIN compatible microscope to another. Should you lose or damage an objective, you can easily replace it rather than have to buy a new microscope.

With regard to eyepieces, as a general rule, the wider the eyepieces the easier the viewing. Ask for Widefield (WF) or Super Wide Field (SWF) eyepieces. Be aware, however, that the width of the lens, itself will decrease relative to the size of the magnification power. In other words, higher power eyepieces have smaller eye ports.


There are four primary types of illumination: tungsten, fluorescent, halogen and LED.

a). Halogen
In summary, a high quality, pedestal microscope should include halogen lighting as standard. Halogen produces a strong, white light and typically, include a variable rheostat so that the intensity of the light can be adjusted. All Omano, pedestal, microscopes use halogen light.

b). LED ¨C Portable Microscopes
LED ring lights are commonly used in portable microscopes and, typically include rechargeable batteries. Portable microscopes and LED ring lights are useful for microscopists who wish to use them outside or where there are limited electrical outlets such as conferences or trade shows.

c). Flourescent Light
Flourescent lighting is typically used in specialist, epi-flourescent microscopes for biological research and similar applications. However, fluorescent ring lights, are typically used as additional light sources in stereo microscopes when more light is required. These ring lights should not be confused with fluorescent microscopes.

d). Tungsten
We recommend against buying a microscope with tungsten lights. They produce yellowish light and excessive heat. No high quality microscope will include tungsten lighting.


a). Iris Diaphragm & Abbe Condenser
When buying a compound microscope, always ensure that the microscope has an iris diaphragm and an Abbe condenser ¨C which all good quality microscopes will include. Both items are found in the sub-stage of the microscope and are used in adjusting the base illumination. All Omano compound microscopes include iris diaphragms and Abbe condensers, as standard.

b). Mechanical Stage
A mechanical stage is also useful for compound microscopes, particularly when viewing specimens at high magnifications. All our full-size, Omano compound microscopes include a mechanical stage with one exception where it is optional.


So far, we have summarized the basic variables that go into buying a microscope. Often overlooked is the quality of service that you will receive and the shipping and returns policy.

a). Knowledgeable Service
At The Microscope Store, LLC, we believe that buying a microscope should be fun! It should not be daunting. More important, a good microscope vendor will have sufficient knowledge and patience to be able to walk you through the above, decision-making process. They will be able to guide you to a microscope that is well-suited to your application. We pride ourselves on this level of service at The Microscope Store, LLC. It is central to our success and is underpinned by a strong sense of traditional business ethics.

b). Returns Policy
That said, everyone makes mistakes! For this reason, we recommend that you only buy a microscope from a vendor with an adequate Returns policy. As this article indicates, there are many variables that go into buying a microscope. In some cases, however helpful the vendor is, the microscope may not quite work out as anticipated. Most reputable microscope vendors have a 14-30 day returns policy, during which time the microscope, (if in it¡¯s original condition and packaging), can be returned for a full refund. At The Microscope Store, LLC, we have a 25-day Returns Policy.

c). Shipping Costs
Finally, it is worth checking the vendor¡¯s shipping policy. Shipping costs can add more than 10% to the cost of a microscope. At The Microscope Store, LLC, we pledge never to make a profit from shipping. See full details on the special shipping offer.
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Microscope Safety
¡¤Never disassemble the microscope as doing so may cause electric shock or damage to the microscope
¡¤Allow the halogen bulbs to cool before touching. Halogen bulbs become extremely hot and may cause burns if touched
¡¤To avoid electric shock or damage to the instrument, unplug the microscope before replacing the bulb.
¡¤Use only the prescribed halogen or fluorescent bulb
¡¤Turn off and unplug the microscope before moving.
Carrying the Microscope
¡¤Always lift the microscope with two hands: one hand on the arm, the other hand supporting the base.
Cleaning the Microscope
¡¤Dust should be cleaned off with pressurized air or with a soft brush
¡¤Clean smudges, fingerprints, oils, etc from the lens with clean lens paper or a soft clean cloth moistened with a small amount of absolute alcohol-ether mixture. If an alcohol-ether mixture is unavailable, use isopropyl alcohol
¡¤Clean the microscope body and stand using a moist, soft cloth with a small amount of detergent.
¡¤Working temperatures are: 32¡ã F-104¡ã F (0¡ãC-40¡ãC). Max. relative humidity: 85%
¡¤Use water only on plastic surfaces
¡¤Do not use paint thinner or other solvents
¡¤Do a final wipe with a moist soft cloth
¡¤Dry all surfaces after cleaning
¡¤Always cover the microscope with the supplied dust cover when not in use
¡¤Store in a dry place
¡¤In humid or moist environments, it is advisable to store the microscope in a waterproof container with a drying agent
¡¤Do not touch the optical lens with bare fingers
¡¤Do not store the microscope in direct sunlight. Sunlight can influence the quality of the specimen imaging.
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Microscope Troubleshooting Tips
Are you having trouble with your microscope? Below is a list of common questions we receive when it comes to microscope maintenance and troubleshooting. If your question is not listed here, please call us at (877) 409-3556 and a technician will gladly assist you.

1). My microscope will not turn on.

¡¤First, check to see if your microscope is plugged in.
¡¤Secondly, check to see if the bulbs are installed correctly: You may have to install or reinstall the microscope bulb. Not all microscopes are shipped with the bulbs already installed. If the bulbs are installed, check to make sure they aren¡¯t loose, which sometimes happens during shipment.
¡¤Have you examined all power adjustments? Most microscopes have rocker switches located on the back, sides and the top to control whether the microscope receives power or not; also, most have dials that control the dimness or intensity of the light.
¡¤Is the fuse in good condition? All microscopes (with cords) have fuses that can be accessed from the outside of the microscope. Depending on the your microscope model, you will either find the fuse on the bottom or back of the microscope. If the glass case of the fuse appears discolored or burned, or you can see broken pieces of the fuse element, this means the fuse is not working. Replacing the fuse will fix this problem. If your microscope blows its replacement fuse quickly, please contact one of our microscope technicians for repair.

2.) I cannot see anything through my microscope.

¡¤Make sure you have removed the protective coverings
¡¤Have you installed the eyepieces? If not, install your eyepieces (Not sure how? See instructions below)

3.) I cannot install my eyepieces.

¡¤Have you removed the protective covers from the eye ports? If not, pull out protective covers.
¡¤Are their retaining screws obstructing this installation? If so, retract with a small slotted screwdriver, such as an eyeglass screwdriver or penknife. Be careful not to scratch the finish on the eyepiece tubes.

4.) I cannot view anything through the trinocular port on my microscope.

¡¤Is a black protective cover obstructing your view? If so, remove the protective covering.
¡¤Is there a silver pull or lever on the side or front of your microscope head? If so, either slide the lever back and forth or pull and push the silver pull. This will transfer the image from the eye ports to the trinocular port.
¡¤Are you attempting to look through the trinocular port without an eyepiece? The trinocular port does not contain an optic for viewing. You may purchase an eyepiece ocular to facilitate this type of use if necessary. Typically the trinocular port is used for digital camera attachments that do not require an eyepiece ocular.
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How to Use a Compound Microscope
Familiarization: First, familiarize yourself with all the parts of a microscope so that you can easily move from one part to another during operation.

Moving and Placement: It is worth remembering that while a good quality microscope will last a lifetime, it is a sensitive scientific instrument that will suffer damage from sharp blows or impact. Always, therefore, carry your microscope in both hands. Grasp the arm with one hand and place the other hand under the base for support. Always place the microscope on a level and stable surface.

Slide Preparation: Microscope slides should always be prepared with a cover slip or cover glass over the specimen. This will help protect the objective lenses if they touch the slide. To hold the slide on the stage fasten it with the stage clips. You can push down on the back end of the stage clip to open it.

Focusing the Microscope:

1.Start by turning the revolving nosepiece (turret) so that the lowest power objective lens is "clicked" into position. The lowest power objective is the shortest one. This objective is the easiest to focus and center the image in the field of view.
2.While looking at the objective lens and the stage from the side, turn the coarse focus knob so that the stage moves upward toward the objectives. Move it as far as it will go without touching the slide.
3.Now, look through the eyepiece(s) and adjust the illuminator and diaphragm until you attain the maximum, comfortable level of light.
Slowly turn the coarse adjustment so that the stage moves down (away from the slide). Continue until the image comes into broad focus. The turn the fine adjustment knob, as necessary, for perfect focus.
4.Move the microscope slide until the image is in the center of the field of view. Then readjust the illuminator or diaphragm in order to attain the clearest image.
5.Once you have attained a clear image, you should be able to change to a higher power objective lens with only minimal use of the focusing adjustment. If you cannot focus on your specimen, repeat the above steps and work from objective to objective until the higher power objective lens is in place.
General Advice

1.You should check to see if your microscope has a rack stop. If it does not have one, then be careful not to allow the objective lens to touch the slide as you may break the slide.
2.When using a monocular microscope, the correct technique is to look through the eyepiece with one eye and keep the other eye open. Most new users, tend to close one eye. While many microscopists do close one eye, you will help avoid eye strain by keeping both eyes open.
3.Finally, remember! When you view a specimen through a microscope, you are viewing an image through multiple lenses. As a result, the image is upside down and back-to-front so when you move the slide to the right, the image goes to the left and vice versa!

Care & Maintenance of Your Microscope

Your microscope will last a lifetime if cared for properly and we recommend that you observe the following basic steps:

1.When finished viewing , lower the stage, click the low power lens into position and remove the slide.
2.Switch off the microscope when not using.
3.Avoid touching the glass part of the lenses with your fingers. Use only special lens paper to clean the lenses.
4.Dust is the number one enemy of a microscope so always keep your microscope covered when not in use. When not in use for extended periods, replace the microscope in its box.
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Microscope Magnification Specifications
Field of View or Field Diameter is very important in microscopy as it is a more meaningful number than "magnification". Field diameter is simply the number of millimeters or micrometers you will see in your whole field of view when looking into the eyepiece lens. It is just as if you put a ruler under the microscope and counted the number of lines.

The chart below will tell you (approximately) what to expect when looking through a microscope with varying combinations of eyepiece and objective lenses. As an example (in green below), a dual power stereo microscope with 10X eyepiece lenses and 1X and 3X combinations of objective lenses, would have total powers of 10X and 30X and your field of view would be 20 mm and 6.7 mm respectively.

This means that an object 20 mm (2 cm, or about 3/4 inch) wide would fill up the whole viewing area at 10X and an object about 6.7 mm wide would fill up the whole area at 30X. As you can see, having the highest power may not be best for your particular application. When you move to greater magnifications, you sacrifice field of view.

Try thismicroscope
Get a metric ruler and place it on the stage of your microscope. Illuminate from above (if you are using a compound microscope, get a transparent ruler or illuminate it with a flashlight). See how many millimeters you can see from left to right. What would be the field of view of this image? (answer at bottom of page)

Other considerations: The working distance is the distance from the bottom of the microscope (lens) to the part of the specimen that is in focus. As you increase the magnification, you decrease the working distance. If you need to work under the microscope, you will need a large working distance. Some special microscopes have extended working distances for these purposes. Zoom microscopes have a fixed working distance throughout the zoom range. When using a 100X objective lens (1000X total power) your working distance might only be 0.04mm (40um). The lens will be extremely close to the specimen! The working distance and the amount of vertical motion of the microscope will also affect the maximum specimen height. Maximum Specimen Height is how tall an object you can put on the stage and still be able to focus on the top part of the specimen.

Note: The numbers below will not be the same for all brands of microscopes

Eyepiece Lenses
  5X 10X 15X 20X
  Eyepieces Eyepieces Eyepieces Eyepieces
1X 5X 22mm 10X 20mm 15X 13mm 20X 9.5mm
2X 10X 11mm 20X 10mm 30X 6.5mm 40X 4.8mm
1X 5X 22mm 10X 20mm 15X 13mm 20X 9.5mm
3X 15X 7.3mm 30X 6.7mm 45X 4.3mm 60X 3.2mm
2X 10X 11mm 20X 10mm 30X 6.5mm 40X 4.8mm
4X 20X 5.5mm 40X 5mm 60X 3.2mm 80X 2.4mm
10X     100X 1.8mm
40X     400X 0.45mm
100X     1000X 0.18mm

High power microscopes usually have 10X eyepiece lenses so we only list one column above the 4X objective.  If you wanted to look at an amoeba that is 150um long (0.15mm) then you would use either the 40X or 100X objectives..  There are 25 mm in an inch and there are 1,000 um (micrometers) in a single millimeter.

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The Microscope Parts and Specifications
Historians credit the invention of the compound microscope to the Dutch spectacle maker, Zacharias Janssen, around the year 1590. The compound microscope uses lenses and light to enlarge the image and is also called an optical or light microscope (vs./ an electron microscope). The simplest optical microscope is the magnifying glass and is good to about ten times (10X) magnification. The compound microscope has two systems of lenses for greater magnification, 1) the ocular, or eyepiece lens that one looks into and 2) the objective lens, or the lens closest to the object. Before purchasing or using a microscope, it is important to know the functions of each part. microscope

Eyepiece Lens: the lens at the top that you look through. They are usually 10X or 15X power.

Tube: Connects the eyepiece to the objective lenses

Arm: Supports the tube and connects it to the base

Base: The bottom of the microscope, used for support

Illuminator: A steady light source (110 volts) used in place of a mirror. If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.

Stage: The flat platform where you place your slides. Stage clips hold the slides in place. If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs. One moves it left and right, the other moves it up and down.

Revolving Nosepiece or Turret: This is the part that holds two or more objective lenses and can be rotated to easily change power.

Objective Lenses: Usually you will find 3 or 4 objective lenses on a microscope. They almost always consist of 4X, 10X, 40X and 100X powers. When coupled with a 10X (most common) eyepiece lens, we get total magnifications of 40X (4X times 10X), 100X , 400X and 1000X. To have good resolution at 1000X, you will need a relatively sophisticated microscope with an Abbe condenser. The shortest lens is the lowest power, the longest one is the lens with the greatest power. Lenses are color coded and if built to DIN standards are interchangeable between microscopes. The high power objective lenses are retractable (i.e. 40XR). This means that if they hit a slide, the end of the lens will push in (spring loaded) thereby protecting the lens and the slide. All quality microscopes have achromatic, parcentered, parfocal lenses.

Rack Stop: This is an adjustment that determines how close the objective lens can get to the slide. It is set at the factory and keeps students from cranking the high power objective lens down into the slide and breaking things. You would only need to adjust this if you were using very thin slides and you weren't able to focus on the specimen at high power. (Tip: If you are using thin slides and can't focus, rather than adjust the rack stop, place a clear glass slide under the original slide to raise it a bit higher)

Condenser Lens: The purpose of the condenser lens is to focus the light onto the specimen. Condenser lenses are most useful at the highest powers (400X and above). Microscopes with in stage condenser lenses render a sharper image than those with no lens (at 400X). If your microscope has a maximum power of 400X, you will get the maximum benefit by using a condenser lenses rated at 0.65 NA or greater. 0.65 NA condenser lenses may be mounted in the stage and work quite well. A big advantage to a stage mounted lens is that there is one less focusing item to deal with. If you go to 1000X then you should have a focusable condenser lens with an N.A. of 1.25 or greater. Most 1000X microscopes use 1.25 Abbe condenser lens systems. The Abbe condenser lens can be moved up and down. It is set very close to the slide at 1000X and moved further away at the lower powers.

Diaphragm or Iris: Many microscopes have a rotating disk under the stage. This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. There is no set rule regarding which setting to use for a particular power. Rather, the setting is a function of the transparency of the specimen, the degree of contrast you desire and the particular objective lens in use.

How to Focus Your Microscope: The proper way to focus a microscope is to start with the lowest power objective lens first and while looking from the side, crank the lens down as close to the specimen as possible without touching it. Now, look through the eyepiece lens and focus upward only until the image is sharp. If you can't get it in focus, repeat the process again. Once the image is sharp with the low power lens, you should be able to simply click in the next power lens and do minor adjustments with the focus knob. If your microscope has a fine focus adjustment, turning it a bit should be all that's necessary. Continue with subsequent objective lenses and fine focus each time.

What to look for when purchasing a microscope.
If you want a real microscope that provides sharp crisp images then stay away from the toy stores and the plastic instruments that claim to go up to 600X or more. There are many high quality student grade microscopes on the market today. They have a metal body and all glass lenses. One of the most important considerations is to purchase your instrument from a reputable source. Although a dealer may give you a great price, they may not be around next year to help you with a problem. One dealer that we can highly recommend is Microscope World. They offer a wide variety of instruments at very competitive prices.
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History of the Microscope
(includes: Who invented the microscope)
During the 1st century AD (year 100), glass had been invented and the Romans were looking through the glass and testing it. They experimented with different shapes of clear glass and one of their samples was thick in the middle and thin on the edges. They discovered that if you held one of these “lenses?over an object, the object would look larger.

Someone also discovered that you can focus the rays of the sun with one of these special “glasses?and start a fire. These early lenses were called magnifiers or burning glasses. The word lens by the way, is derived from the latin word lentil, as they were named because they resembled the shape of a lentil bean (look up lens in a dictionary).

These lenses were not used much until the end of the 13th century when spectacle makers were producing lenses to be worn as glasses.

The early simple “microscopes?which were really only magnifying glasses had one power, usually about 6X - 10X . One thing that was very common and interesting to look at was fleas and other tiny insects. These early magnifiers were hence called “flea glasses?

Sometime about the year 1590, two Dutch spectacle makers, Zaccharias Janssen and his father Hans started experimenting with these lenses. They put several lenses in a tube and made a very important discovery. The object near the end of the tube appeared to be greatly enlarged, much larger than any simple magnifying glass could achieve by itself! They had just invented the compound microscope (which is a microscope that uses two or more lenses).

Galileo heard of their experiments and started experimenting on his own. He described the principles of lenses and light rays and improved both the microscope and telescope. He added a focusing device to his microscope and of course went on to explore the heavens with his telescopes.

Anthony Leeuwenhoek of Holland became very interested in lenses while working with magnifying glasses in a dry goods store. He used the magnifying glass to count threads in woven cloth. He became so interested that he learned how to make lenses. By grinding and polishing, he was able to make small lenses with great curvatures. These rounder lenses produced greater magnification, and his microscopes were able to magnify up to 270X!

Anthony Leeuwenhoek became more involved in science and with his new improved microscope was able to see things that no man had ever seen before. He saw bacteria, yeast, blood cells and many tiny animals swimming about in a drop of water. From his great contributions, many discoveries and research papers, Anthony Leeuwenhoek (1632-1723) has since been called the "Father of Microscopy".

Robert Hooke, an Englishman (who is sometimes called the “English Father of Microscopy?, also spent much of his life working with microscopes and improved their design and capabilities.

Little was done to improve the microscope until the middle of the 19th century when great strides were made and quality instruments like today’s microscope emerged. Companies in Germany like Zeiss and an American company founded by Charles Spencer began producing fine optical instruments.

Today, there are no microscope manufacturers in the US and most of the microscopes come from Germany, Japan and China. Toy plastic microscopes should be avoided as they do not achieved the level of quality of the basic instruments with metal frames and glass lenses.

Because of foreign production, quality microscopes have become affordable for all. Zaccharias Janssen, the inventor of the microscope would marvel at the quality of even the most basic microscopes found in schools today.
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Evaluating a Microscope
When evaluating microscopes,here are some items that you might check.

¡öCheck the size of the microscope. Many of the introductory and elementary student models are 3/4 size or smaller. This is ok for younger students but children over 13 years old and adults might prefer a full size instrument. Generally these smaller microscopes are from 11 to 12 inches tall and the full size microscopes are 14 inches tall and up.

¡öIf you do choose a 3/4 size microscope we recommend you select one with a stationary stage and a moving tube (to focus). The instruments with the moving stage and fixed tube seem to have a universal problem with stage drift. In the full sized varieties, this is not a problem so the moving stage is not an issue with them. See more on stage drift below.

¡öMaterials and workmanship: Basic frame and components should be metal, although some small parts may be of plastic. Evaluate the general appearance of all optical and metal surfaces.

¡öCheck the focusing mechanism: The rack and pinion type is the most reliable and should move smoothly when the focus knobs are turned. There should be no rough spots. We do not recommend microscopes with a single "intermediate" focusing knob. If your microscope goes to 400 or 1000X, it should have both coarse and fine adjustments.

¡öCheck dovetail in the focusing track (rack and pinion): Look at the type of metals used to assure that improper materials will not cause problems later. Check for excessive grease on moving parts.

microscopeThe rack and pinion focusing mechanism is a very important component. A round cog-wheel type gear (the pinion, not shown) engages the rack (teeth, shown) and should offer smooth motion throughout the focusing range. The dove tail (shown) is the channel on which the rack runs and should be finely machined.

¡öWhen focusing, some microscopes have a moving stage, others have a moving eyepiece tube. If the stage moves when you focus, check stage drift by pushing down slightly on the stage with fingers. It should not move. If the stage is stationary and the eyepiece tube moves, likewise check drift by slightly pushing down on the eyepiece. On some 3/4 size microscopes with a moving stage, just moving the slide around on the stage will push the image out of focus! This is extremely frustrating when you are trying to move a slide around at high powers.

¡öLook at the alignment of the stage and nosepiece: For example, if the stage is tilted just a tiny bit, your specimen will continually be out of focus on one side or the other.

¡öCheck for "backlash" by focusing all the way to the top and bottom and try to turn the knob further, looking for slight motion. This tells you how well the rack and pinion gears are matched.

¡öCheck the slip clutch by continuing to turn the focus knob even after reaching some resistance.

¡öCheck parfocallity: With a slide on the stage, the image should remain relatively close to focus when changing objective lenses. Only a slight adjustment should be required to sharpen the image as objectives are changed.

¡öCheck parcentricity: Start with the lowest power objective and center your specimen. Move up to successive objective lenses and the area should remain relatively centered.

¡öCheck for cleanliness: With no slide on the stage, dial in your highest power objective lens, adjust the diaphragm to the smallest opening, turn on the illuminator and look through the eyepiece lens. If you see dust particles, turn the eyepiece lens. If the dust moves, it is on the eyepiece. If it doesn't move, it is likely on the internal prisms.

¡öThe quality of the objective lenses is one of the most important characteristics of a fine microscope. The better the lenses (and usually, the more expensive the microscope!), the sharper the image. In a side by side comparison, you might be able to notice a difference!
microscope microscope
High quality lenses produce crisp, clear images Poor quality or dirty lenses will produce poor, low resolution images
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