“Don’t bother with binoculars, I want a telescope,” many beginners say.
But binoculars are telescopes! They’re simply two small telescopes side by side, with some optical additions to bring the eyepieces close enough together that you can comfortably look through both at the same time. Unlike large telescopes, binoculars are intuitive and easy to use. They provide a vertical image and a wide field of view, making it easy to point them at an object and find what you want. And they take no time to install and align either. Just hold it in your hand and point it at the stars. Binoculars are particularly useful for observing the large craters of the Moon, the moons of Jupiter, the occasional comet, observing the Moon and the planets alone at sunrise or sunset, and, once you know how to find them, you can also observe large clusters and groups of stars throughout the sky.
All binoculars are marked with two main parameters: magnification and aperture. For example, a pair of binoculars labeled 7×50 means it has 7x (7x) magnification and a 50mm objective diameter. The larger the lens, the more faint and detailed the objects you can see. A 50mm lens will pick up 50-60 times more light than with the naked eye, meaning you’ll be able to see objects up to 50-60 times more dimly.
Binoculars with 6x to 10x magnification are extremely useful for stargazing and are usually light enough to keep on hand for short observing sessions. Higher magnification means you will see more detail and the background sky will be darker. But you’ll also have a narrower field of view, and it can be difficult to hold a large pair of binoculars steady enough in your hand to see details when even a vibration in your arm interferes with your view of the subject. For manual use of binoculars, a magnification of about 7 to 8x is optimal and 10x is the maximum.
Compare 7x and 10x magnifications. Credit: thegioithienvan.com
Due to their large aperture, a pair of 10×80 binoculars will help you see fainter objects than 10×50 binoculars. But in return, larger lenses also weigh more, and heavier lenses over 50mm will make it difficult to hold in your hand for a long time.
Binoculars also allow viewing with both eyes, providing a comfortable and natural feeling, and help many observers gain a greater sense of depth, although this is only an illusion for subjects with such a large gap. You also avoid distracting effects from other objects surrounding the viewing area. In reality, out-of-focus objects also appear brighter when viewed with both eyes.
Some binoculars are marked with the size of the field of view in degrees or “feet at 1,000 meters”. This tells you the width of the scene you are going to watch. For a lens of a particular size, high magnification means a small field of view. You will therefore see more of the sky with a pair of 10×50 binoculars than with a pair of 7×50 binoculars. All other things are equal.
Another important binocular measurement is the “exit pupil,” also known as eye circle, which is the size of the disk of light when you look through the eyepiece of a binocular held at arm’s length. Aperture is simply the ratio of aperture to magnification. A pair of 7×50 binoculars has an exit hole of 50/7 = 7 mm (rounded), and a pair of 7×35 binoculars has an exit hole of 5 mm.
You need to make sure that the binoculars’ exit holes are no larger than your pupil size when seeing in the dark. Before the age of 30, most people have pupils of around 7 mm. But they decrease by 1 mm every 10 to 15 years. At 50, it will not be a problem to use binoculars with an exit hole greater than 5-6 mm. But if you’re older, a pair of 7×35 or 8×42 binoculars (both with around 5mm hole) might be a better choice than 7×50 binoculars (with 7mm hole). On average, binoculars are not that expensive.
Illustration of the size of the exit hole or eye circle of binoculars. Credit: bhphotovideo.com
Illustration of viewing angle and field of view. Credit: Credit: bhphotovideo.com
How to choose binoculars?
When choosing binoculars, look for a pair that uses Porro prisms, which are classic style binoculars in which the objective and eyepieces are not coaxial. Binoculars that have direct vision are binoculars that use domed prisms, and a good pair of them are very expensive. You don’t have to pay for premium quality. Binoculars with zoom functions or built-in cameras should be avoided. They are not useful for astronomical observations.
When choosing a pair of binoculars, try to look at the reflected light in front of the lens. If the lens has a good anti-reflective coating, it will appear mostly dark, with some reflected color. If the lens is white or ruby red, don’t buy it. Looking through the objective lens to the inner prism, an anti-reflective coating will reveal a colored prism surface. A white surface on the prism means there is no anti-reflective coating. A poor or untreated anti-reflective coating will create a “ghost image” of bright objects such as the Moon and planets.
Cross-section of a pair of binoculars using a domed prism (left) and a Porro prism (right). Credit: bhphotovideo.com
Move the binoculars away and point the eyepieces towards your eyes. Look at the shiny disk of the stoma. This bright disk appears round if the prism uses high quality glass (called BAK-4 glass). If the light disk is square in shape, the prisms are made of lower quality BK-7 glass. Not bad, but not optimal.
If you are nearsighted or farsighted, you do not need to wear glasses when viewing through binoculars. But if you have astigmatism, you will need glasses.
You should also check the sharpness across the entire field of view. A standard pair of binoculars will stay sharp all the way to the edge of the field of view. It may not be sharp around the edges, but if it doesn’t stay sharp or is distorted a lot, move on to another pair of binoculars.
The binocular exit hole light disc uses high quality BAK-4 circular glass prisms and low quality BK-7 square glass prisms.
Credit: thegioithienvan.com
Choose Stargazing Binoculars
So now you know a bit about how to choose binoculars for astronomy and why binoculars are a reliable and enjoyable tool for stargazing. But which brand and model of binoculars is the darkest for you? This of course depends on your situation and your financial capabilities. There are dozens of good models available today, as well as many modern binoculars made of high quality, lightweight materials at reasonable prices. It’s the best time in history to get a good pair of stargazing binoculars.
Let’s start with the price. The expected price is around 2-6 million VND for a good pair of stargazing binoculars. Lower prices often result in blurrier images near the edge of the field of view, and poor quality optical coatings cause blurry images and ghosting. Very expensive binoculars will provide bright and powerful images throughout the entire field of view, and it’s good if you can spend 10-15 million or more. But there is no need to spend so much money.
Choose stargazing binoculars with an aperture of 35mm to 60mm and magnification of 7x to 10x. Thus, a pair of 7×35 binoculars is the smallest acceptable for astronomical observations. A pair of 7×50 binoculars is preferable because they offer the same magnification but a wider field of view.
If you’re over 40, you might not need the 7mm exit hole of 7×50 binoculars, so you might want to consider the 8×42 for slightly larger images. If you’re not concerned about weight, a pair of 8×56 or 10×50 binoculars are a great choice for stargazing. Likewise, 9x63s are excellent, although they can be a bit heavier. Any binoculars above 10x will produce shaky images. Any binoculars larger than 63mm will be very heavy and difficult to hold for long periods of time.
As for brand, binoculars made by Orion, Celestron, Nikon and Vega are often good choices. Not all manufacturers have all the magnification and aperture configurations of their binoculars, but there are enough options to find something that will do the trick.
Everything revolves around binoculars. Once you’ve chosen your very own pair of binoculars, get out there and point them at the Sagittarius cloud, or the Pleiades star cluster, or its bright stars and nebulae, Orion, and you’ll be absolutely amazed at the beauty you see.
To be continued…
You can refer to some types of binoculars at the Association store with all the required criteria: deepsky2000.net/cuahang, thegioithienvan.com
According to Phan Hien – VLTV:
Nguồn: Beginner’s Guide to Choosing Binoculars and Telescopes for Stargazing
