Microscopes are a tool of both pleasure and profession. Being such a flexible optical device there are many units to choose from. This guide will help you understand the basics of a microscope so you can make an educated purchase.
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!
The Types of Microscopes
The type is the most important thing when choosing a microscope. You couldn't use a compound microscope for looking at rocks and you couldn't use a stereo microscope for looking at bacteria. A general rule of thumb is:
Compound = Biological but high power, everything you require slide preparation for.
Stereo = Industrial but low power, good for whole objects that cannot be used in a slide. No preparation required.
If you’ve taken biology or watched television, you’re familiar with the basic Compound Microscope. It can achieve magnification upward of 2000x, with most work being done in the range of 400-500x. With its high-power capabilities, it is mostly widely used in biological and scientific situations. Cellular detail can begin to appear at 40x and, at 400x, significant detail can be seen. You will need at least 100x to study bacteria.
Microscopes come in many shapes and forms, with varying levels of intricacy and accuracy.
'Compound' refers to the optical system that produces the high magnifications. The objectives start as low as 4x and typically will go up to 100x. With the right eyepieces, it’s not hard to see how those 2,000x magnifications are possible. The light travels in a single path from the light source to the eyepiece — even if a binocular head is being used — causing images to appear two-dimensional. When looking through the eyepiece, the image is uncorrected, so it will appear upside-down and backward. This means that moving a slide to the right will make the image move left, and moving it forward will make the image go back. Generally, when looking at specimens at the cellular level, this doesn’t cause any confusion or discomfort—it just might take some getting used to when starting out.
These are low-power devices with two eyepieces that are used primarily for inspection purposes. They tend to stay in the 10-40x range and can go up to as much as 100x, to observe details in larger solid specimens like fossils, stamps, coins, or circuit boards. Unlike a Compound Microscope, the Stereo Microscope most commonly uses light from a top-mounted source to illuminate the sample or subject—as opposed to being lit from below and through the sample as with a compound microscope. Two independent, or stereo, light paths produce a true three-dimensional image when you look through the binocular head. This provides a depth to images and gives the user better resolution and perspective over a compound microscope that produces two-dimensional images due to its single-light path system.
The current connectivity we have become accustomed to in our everyday lives has also improved microscopy and our ability to view and share it. As we’ll see below, once images are digitised, the possibilities for sharing between a group of people, a class or lecture hall, or via the Internet become almost infinite. Just a few years ago, schools and institutions were required to purchase dozens of microscopes, and those who couldn’t afford them were forced to have large groups of students huddle around a single instrument, taking turns. These days, a school or institution can greatly reduce its purchasing and simply stream the images to projection screens, computers, smartphones, and tablets. Doctors deployed to a natural disaster area can stream or email images to colleagues on another continent for diagnosis and treatment.
Lastly, let’s talk about price. Microscopes are available in an incredible range of prices, from $50 toy microscopes to professional models from German and Japanese manufacturers that can cost as much as a new Mercedes-Benz, literally. Toy models are obviously unsuitable for serious use, but few of our readers will have the inclination (or budget) to spend thousands on a professional model. Fortunately, there’s a happy middle ground of inexpensive, high-quality microscopes in the $200 to $2000 range. We’ll focus on that category.All of these microscopes are Chinese-made. The best of the Chinese microscopes are very good, both optically and mechanically. The more you pay, the better it gets.
Microscopes are not scary or overly complex devices. They are designed to be easy to use and to be as flexible as possible. We only covered the basics in this guide.