There are a number of factors to take into account when buying your first pair of binoculars for astronomy. All binoculars are listed with two numbers separated by an X; for example, 8x32 or 10x42. The first number is the magnification level, and the second the size of the lens in millimetres.
- The magnification level shows how many times closer something will appear. A level of 7, for example, will make something 70 feet away appear to be 10 feet away.
- Fixed magnification binoculars are best for astronomy; variable zoom ones make the image too dark.
- It can be harder to control higher magnification binoculars; they amplify any movements you make, including any jerks and shakes.
- Larger lenses allow more light into the binoculars, making the image clearer.
- More expensive lenses are generally brighter and offer greater clarity.
- Astronomy lenses need to be at least 40mm wide, preferably over 50mm.
- Larger lens sizes can be too heavy to be hand-held.
- Greater magnifications become difficult to hold steady; anything over 10x can be unsuitable for hand-held use.
- Mounting binoculars on a tripod makes them more stable and easy to aim.
- Mounted binoculars allow you to use giant lens and magnification lenses that offer telescope-like levels of close detail.
Exit lens / Eyepiece size:
- The size of the exit lens needs to match the size of your dilated pupil in the dark.
- If the lens is bigger than your pupil, the image will appear dimmer.
- Your pupil will dilate to different sizes as you grow older.
- Generally speaking, people under 30 should look at a 7mm lens, over 30 a 6mm lens and over 40 a 5mm lens.
There are two main types of binocular design; Porro and Roof.
- Porro form a wider "M" shape due to the positioning of the internal prisms.
- Roof binoculars are narrower and H shaped.
- Due to the more complicated technology, Roof binoculars are often more expensive.
- Porro binoculars can let more light in, but are generally more fragile than Roof models.
- Porro binoculars are often more bulky than Roof designs.
- Make sure your binoculars have enough waterproofing to cope with the British weather.
- Roof designs are easier to weatherproof.
- Lenses can come with special protective coatings that help repel water or prevent damage.
Ease of use and comfort:
- A good focus system will allow you to swiftly and smoothly get a sharp image without any effort.
- The focus ring should offer just enough resistance that it’s easy to turn and keep in focus when the image is pin-sharp.
Your ideal first pair of binoculars will feel natural in your hand, sit comfortably against your eyes and be a weight you can comfortably carry for a long period of time unless you are mounting them. Binoculars are excellent for viewing objects in our solar system, and the wide viewing angle can give gorgeous views of features such as large star clusters. While a powerful telescope will always show closer detail, binoculars offer a cheaper and more portable way to view the heavens. Happy stargazing!
Always refer to the manufacturer’s manual for specific details.