On the surface, telescopes and microscopes might appear to have similar functions. They both have lenses, they both magnify objects, and they both bring the invisible world into focus. But underneath, these two devices use opposite mechanics to bring images to your eye. In fact, their opposite qualities are what determine the behavior of the light captured within them. Understanding the way each device works will help differentiate the two in your mind.
The primary difference between a microscope and a telescope is the focal length. This is the length through which light travels inside the device.
The longer focal length of a telescope makes images smaller, which means you can make planetary objects shrink to fit inside your eyepiece. The shorter focal length of a microscope makes images larger, which means a molecule can appear the size of a baseball. While both devices use a focal point (the place where parallel rays of light converge) to capture an image, the focal length ultimately determines if an object will appear shrunken or enlarged.
Deep-sky objects like planets and moons don’t create their own light. This means a telescope must pull in as much light as possible to capture an image. The larger the lens diameter, the more light is absorbed, creating images far beyond the range of normal human sight. But a microscope comes equipped with its own light source (or can utilize the natural light of the environment), which makes smaller diameter lenses most effective. Too much light and your microscopic specimen will look blurred.
The two devices are also opposite in their adjustability. A telescope has a fixed objective lens, but a changeable eyepiece. This means the object must be far away to see a crisp image of it. Telescopes have a big footprint, too. They can take up a corner of a room or require an entire building to house them.
A microscope has a fixed eyepiece and three or more changeable objective lenses. If you want to focus on an object, it must be close. Their footprint is typically small, taking up only a small spot on your desktop. Even the largest microscopes are dwarfs in comparison to the largest telescopes.
While these two devices are opposites in most respects, their power to magnify the invisible has changed the way we understand nature and the cosmos. Whether you need to examine the galaxy residing in a bacterium or look outward to a galaxy full of stars, magnification will change the way you see the world.
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