Want to bring the cosmos closer without breaking the bank or your bag straps? A monocular might be just the ticket. But what are they and how do they work? In this explainer, we'll be delving into the background of this optical device, defining its primary uses and jumping into the science of how they capture and convert light into magnifiable images. We also explore and discuss the practical application of monoculars in various settings and highlight their areas of maximum utility.
Finally, for the technically minded, we provide insights into how glass coatings enhance captured images and outline the specific functions of different coatings in addressing issues like chromatic aberration.
What is a monocular?
A monocular is a small telescope that can be hand-held and used with one eye. They magnify objects that are some distance away using a series of internal lenses and/or mirrors that focus light on an eyepiece, creating an image.
They are much smaller and lighter than a telescope but tend to have much smaller magnification ranges. In particular, they are useful for watching wildlife or wide-field observing of the night sky, viewing sports events in detail, and are especially portable so they are handy for hiking.
Several people have been credited with the invention of the monocular. These include:
Johann Lippershey, a Dutch spectacle maker who, in the 17th century, patented the idea of an optical device that could magnify distant objects.
Charles Barbier de la Serre, is credited with inventing the monocular in 1822 but never built one.
Joseph Nicéphore Niépce, built the first working monocular in 1862 based on Barbier's design.
How do you operate a monocular?
Monoculars can be held comfortably in one hand. Most designs incorporate a rubberized outer casing that provides a good grip. They mostly come with a lanyard for throwing over the neck, and the bigger devices will often have a strap fitted to the side of the body to further improve the grip.
It's worth remembering a few safety tips, such as not looking directly at the sun or other bright objects and being stationary when using them. It's a good idea to keep the other eye open when using a monocular in low light levels to help with balance. The larger the magnification, the more likely a tripod/monopod will be of use. Most monoculars have tripod mounting threads built into the body.
There are mainly two types of focus placement in monocular design: one where the focus wheel is attached to the top of the body and the other where a collar is built into the body.
Locate the focus wheel on your device and aim toward a distant object. Then, twist the focus until the view becomes clear and free from blurring. In practice, the roof-mounted focus wheels tend to be more convenient, especially for one-handed operation. In the wet, the body-mounted ring focus designs tend to be more difficult to use.
How does a monocular work?
Monoculars operate through the use of lenses and prisms to gather and manipulate light. When light enters the monocular through the objective lens located at the front of the device, it is initially inverted, meaning that the image appears upside down. The light then travels through the monocular and encounters a prism, which serves to erect the image back to its original orientation.
While most modern monoculars utilize a roof prism for this purpose, some models still feature porro prism-equipped optics. The erect image is then transmitted to the eyepiece lens, where it is magnified for viewing. Although often described as small telescopes, monoculars have very different light paths through their lenses. Telescopes have a straight optical path, whereas monoculars fold the light passing through them using prisms.
This enables the monocular to be much shorter than a telescope and, therefore, much lighter and more portable. The downside of this smallness is that it limits the amount of magnification possible. The sweet spot for monocular magnification is 8x zoom.
Any bigger than this, the monocular becomes harder to focus, heavier, and will have a smaller field of view and less ability to use in low light levels. It's tempting to think that more magnification is better, but this isn't true with most monoculars.
What are lens coatings and why do they matter?
Monoculars typically make use of anti-reflective lens coatings, and their use is improving constantly. Several categories of coatings are used in monoculars, from coated to fully multi-coated.
The coatings work by interfering with certain wavelengths of light, eliminating their reflection; therefore, more light enters your optics and can pass through to your eyes. In fully multi-coated monoculars, all glass surfaces have multiple coatings, resulting in 90-95% light transmission.
Certain roof prism binoculars are equipped with phase coatings to address a potential issue with light divergence as it passes through the prism assembly. This divergence can cause the emerging light to be out of phase, resulting in a lower contrast image. By applying a special coating to compensate for this divergence, phase-coated monoculars can produce brighter and more vivid images. It's worth noting that Porro prism binoculars do not require phase coatings due to the simpler optical path through the prisms.
Factoring in their utility and portability, monoculars are certainly an appealing option for both skygazing, wildlife watching and more. We've alse compared telescopes to monoculars if you're unsure which to go for. As excellent as monoculars are, it's important that you buy the right optical gear for your purposes.
If our explainer has swayed you, and you're ready to explore the wonderful world of monoculars, we've rounded up the best monoculars you can buy.
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