Optical devices and instruments use known properties of how light behaves and interacts to allow us to observe, record, and even enhance images. It has found wide use from everyday stuff we use like computer monitors to cameras, to more specialized applications like electron microscopes and spectrometers.
Furthermore, a lot of terms about these devices have made it through the common language, especially the pair of magnification and resolution. While they sound interchangeable, the two are completely different in function and purpose. Here’s what you need to know about the difference between magnification and resolution.
Perhaps optical instruments in general can be traced back to the microscope and the telescope. The commonly-accepted belief is that the microscope came first, used to enlarge small objects and observe them in greater detail. It was believed that this concept was reversed, which led to the development of the telescope. Since then, their magnification and resolution capabilities has only improved, giving us access to objects a hundredth of a human hair’s width, as well as viewing objects beyond our solar system.
The telescope and the microscope were originally created to magnify objects not visible to the naked eye. Magnification, therefore, refers to the capability of making an object appear larger. This applies to microscopic objects like cells or atoms in the case of microscopes, and planets and other celestial bodies for telescopes. It is usually expressed in the number of times, or the degree, in which magnification can be conducted–10X, 100X, and more.
On the other hand, the word resolution has become ubiquitous in the age of computer monitors, LCD televisions, and smartphone camera. Simply put, resolution refers to the level of detail afforded by an image or an instrument providing it. It can also be defined as the degree to which two separate objects can be distinguished from one another–in the event of digital displays, between pixels. In images and videos, resolution is usually expressed in pixels per inch (PPI). A higher resolution means more pixels are displayed per inch, with each of these pixels corresponding to a specific color. This is why low resolution images look blurred and higher resolution ones have clearer, crisper image. For context, the human eye reportedly has a resolution of 576 megapixels compared to the 12 megapixels found in an iPhone 13 camera.
While the two are conceptually independent from each other, they are interconnected in real-world applications. This is important, especially if you’re looking for a camera or an SEM product to purchase.
Generally, as you try to magnify objects in distance, the resolution starts dropping. A basic instance is that as you zoom in an image, the smaller area becomes more blurred and pixelated until you reach squares of solid colors. The glass lenses commonly used in optical devices are inherently irregular on a microscopic level. This also explains why, in cameras, focusing on an object at a certain distance could create a blurred effect to other elements in the photo.
To maintain an acceptable resolution at high magnification levels, multiple lenses are used together. An ocular lens provides magnification, coupled with an objective lens that help increase resolution. Usually, these two are used with a numerical aperture or light range angles.
However, there are still issues regarding both magnification and resolution. For example, magnification is actually relative and could be limited by the resolution of the device. In a digital microscope, you can sometimes see images with the magnification being indicated. If this saved image is displayed or projected onto a larger screen, then the actual image magnification should also be larger than what is indicated. Additionally, while you can project a high-magnification image onto a larger wall, you’ll see that the images don’t get any clearer. This is called the empty magnification point, where you can continue enlarging the image but with no new detail being revealed.
This is why for scanning electron microscopes, which use electron beams instead of conventional light to magnify objects, they usually include a scale bar to provide context about the magnification of the image. Regardless of where you display or project the image, there will be a reference included.