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Since Robert Hooke spied compartments housed in a bit of cork in 1665 and introduced the term “cell,” the microscope has become an invaluable tool for scientists, educators, students, and professionals. For the novice user, wading through the abundance of technical information when selecting a microscope for purchase can be intimidating, but focusing on a few key items will greatly simplify the task.
First, how will the device be used? There are several types of microscopes, each suitable for a specific purpose:
Compound Microscope: This is the most common design. It's light-illuminated, two-dimensional, and used for viewing individual cells. This type has high magnification but low resolution.
Stereo or Dissection Microscope: These are light-illuminated and three-dimensional, and used for dissection and to look at larger specimens. Individual cells cannot be viewed as this type has high resolution but low magnification.
Electron Microscope: Microscopes of this type fall under two categories. Both are electron-illuminated, have high resolution and high magnification. However, they are outrageously expensive, and thus, not generally purchased by the novice user. They differ in the following ways:
Scanning Electron Microscope (SEM): This type is used for three-dimensional exterior views of specimens.
Transmission Electron Microscope (TEM): This type is suitable for two-dimensional viewing of thin specimen slices.
Once the appropriate type has been determined, look for a device with solid construction. Check to ensure that it is made of metal and not just plastic coated to look like metal, as plastic microscopes have a short life span. Stereo microscopes should be assessed for an adequate staging area to accommodate specimens, and compound versions include either metal clips to hold slides that can be moved with fingers, or mechanical arms that can move slides more precisely with knobs.
Lenses are the next item to consider. Compound microscopes should have a minimum objective lens magnification of 4x, 10x, and 40x. Paired with a standard 10x eyepiece, this results in an overall magnification of 1000x. An appropriate light source should also be included, preferably cool fluorescent. Check on availability of bulbs before purchasing a particular microscope because some bulbs are more difficult to locate and all will need to be replaced at some point.
Achromatic lenses are ideal. These lenses are color corrected and will enable the viewer to see the true colors of a specimen. Without this feature, some parts of a specimen might not be viewable. Next, consider the level of acceptable focus and aberration. Plan objectives indicate 100% focus and no aberrations, but these are quite expensive and only necessary for medical and professional use. One step down is the semi-plan objective which is 80% focus, meaning the center 80% will be without aberration, but these are still too costly for most home users. The typical achromatic lens is 60% focused, and this is fine for an amateur.
If children will be using the microscope, a wide field eyepiece will make viewing much easier, and it will also allow for more of the slide to be viewed at once, minimizing the need to move the slide around. For adults, a binocular, or two-piece eyepiece, device is the most comfortable, but children may fare better with a monocular, or one-piece eyepiece, device because it can be difficult for a child to properly adjust the width between eyepieces.
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