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Choosing the right binoculars

Ian MacLean | Guest contributor

When you want to get up close to the world around you for things beyond your “naked eye” vision, binoculars are usually the first optic of choice. However what is a good binocular, and what sort of binoculars suit different applications?

There are few binoculars that work well in ALL situations. So we hope this will help guide you in finding the binoculars that best suit you and your circumstances. Factors that determine which binoculars will work best for you:

  1. Purpose – No one binocular does everything in all circumstances, so decide what their primary use is going to be.

  2. Magnification – How much detail do you need to see? For example, reading small writing or fine details at a distance requires a larger magnification.

  3. Aperture – The size of the lens, at the front of the binoculars, which determines the amount of light gathered by the binoculars.

  4. Image quality – This will be largely determined by lens and prism quality.

  5. Binocular type – The two main types being Porro Prism and Roof Prism designs.

  6. Build quality – This will affect both the functionality and longevity of your binoculars.

  7. Budget – What is your realistic budget as this will determine the compromises you may need to make.

  8. Portability – The size and compactness of the binoculars. This also affects budget as more compact binoculars are generally more expensive.

  9. Warranty and serviceability – Do you want a set for life, or is five years OK?

  10. Functionality – How they feel in the hand (comfort), focuser operation, diopter eyecups, and how they look.


The magnification, aperture, size and stability of binoculars will determine their suitability for a particular task. We will deep dive into those features in this article. However here is a general guide:


Binos generally need aperture to gather faint starlight so 10x50 or even 15x70 porro prism are popular and effective.


Requires good clarity, portability and moderate light gathering, plus close focus at times, so 8 or 10 x 42 ED roof prism are most popular.


Applications require good aperture for low light, stability and ruggedness in a wet and moving environment, so 7x50 “Marine” Porro are the binoculars of choice.


Binos can be found and the 8x42 ED nicely fills this spot: not forgetting the image-stabilised binocular that is stunning in almost ANY environment!

Magnification and aperture

This is represented by the stated size of the binoculars, eg: 8x42 (see Figure 1 below).

The first number represents magnification (i.e. 8). This determines how much detail you can see, especially at mid to long distances. Magnification can range between 6 and 25, with 15x bringing the highest practical magnification that can be hand-held (under the right circumstances). Any more than 15x magnification is too difficult to hold steady without mechanical support (eg a tripod or monopod), or the purchase of “Image Stabilised” binoculars.

The last number represents aperture (i.e. 42) which is the diameter of the lens. This determines how much light reaches your eyes. This can be anywhere between 20mm and 150mm. Larger apertures such as 50mm or 70mm are great for astronomy or long distance viewing.

BOTH numbers will determine the application to which the binocular is best suited.

Figure 1: 8x42mm Kson TK-214-0842 Waterproof Phase corrected Roof Prism Binoculars

Image quality

The quality of the image, that is to say the colour correctness; image sharpness across the field of view; contrast between dark and light; depth perception; and field of view width; are your main considerations.

This is determined by a number of factors, the first and most important being the prism glass material, separating cheap and ineffective binoculars from those of higher quality. BK4 glass is needed to provide clear and sharp images across the field of view. BK7 is the inferior quality glass used in cheap binoculars (usually under $100).

Roof prisms are a compound design, coated with aluminium, silver or dielectric coatings, each giving successively greater light transmission. Beyond entry level binoculars, the prisms should be “Phase Coated” which gives a noticeable improvement in contrast and image brightness.

Beyond this, the prime or objective lens coating is of great interest. Binoculars should be fully multicoated (FMC) as a minimum. Beyond this, ED (extra low dispersion) glass prime lenses are the best, dramatically reducing chromatic aberration (false colour). Often these binoculars will have hydrophobic (water-repelling) coatings as well (see Figure 2 below).

Figure 2: Zeiss TERRA ED 10x42 Binoculars

Binocular type

The two main types of binoculars are Porro Prism (full size) and Roof Prism (compact) (see Figure 3 below).

Porro prism binoculars are generally less expensive and have full light transmission due to their regular BK4 glass, uncoated prisms. However, most porro prism binoculars do not come with the ED glass objective lens and phase corrected coatings that advanced roof prism binos come with as standard.

Roof prism binoculars are more compact, portable and lighter but require sophisticated coatings (aluminium, silver, or dielectric) to make their compound prisms work as well as standard porro prism binoculars, adding to their cost in the high-performance models. As previously mentioned these enhanced features mean that the best performing binoculars are going to be advanced roof prism vs porro prism binoculars.

Figure 3: Porro vs Roof

Build quality

This will affect the capabilities of the binocular’s focus; smoothness of the eyecup pop-up action; hinge functionality; prism stability in adverse conditions; waterproof (IP) rating; the ruggedness of the body; and the quality of the outer skin material.


If you have under $100 to spend, you are generally looking at a non-waterproof and optically inferior BK7 prism model. Around the $200–$300 mark, there is a wide variety of quality, full-size (porro prism) or entry level roof prism (FMC) binos available. $300–$450 will get you phase-corrected roof prism binoculars ideal for the keen observer of the natural world on a budget. At $500 and above, your binoculars should have ED glass lenses and close focus capability (as close as 2m). You will find this in brands such as Vanguard, Bushnell, and Celestron. These are great for birdwatching in high contrast lighting situations where lesser optics will show false colour due to chromatic aberration. The bigger 10x50mm aperture makes a superior Astronomy Binocular.

Example: Bushnell Forge 10x42 Binoculars price circa $1,000

Beyond that you can expect highly regarded brand names such as Steiner and high-end Bushnells, with long warranties and excellent build quality. That’s in addition to all the top-end features previously mentioned, such as FMC lens, dielectric prism mirrors, phase-corrected and highly shockproof which should be included.

Brands such as Fujinon and Canon have a range of electronically controlled gyroscope-stabilised binoculars capable of delivering high powered clear and sharp views up to 16x.

Above this price range ($2,000+) are some of the most highly regarded brands of uncompromising optical and build quality such as Zeiss, Swarovski, Nikon (EDG), Leica & Steiner (Wildlife) built to last a lifetime.

Example: Zeiss Victory 10x42



The most portable design is the 'clamshell' where the two barrels fold in on the central bridge and focuser. One of the best examples of this type of bino is the Steiner Safari series (below), one of our most popular ultra-portable binos with quality optics. The optics are very satisfying but the downside is a smaller aperture, generally 22–28mm.

Compact roof prism

Most commonly seen as an 8x32 combination and available as a size variant on most models of roof prism binoculars, this suits the person with smaller hands, or who is very weight conscious for both using and transporting the binoculars. The higher-end models can out-perform mid-priced full-sized roof prism binos.

Full-sized roof prism

This size includes 8x42 and 10x42 with a few brands going up to 44mm aperture. These are typically around 600–700g in weight. The big advantage is the aperture and light gathering ability that gives. Examples are the previously shown Bushnell and Zeiss binos.

Warranty and serviceability

Do you want a set of binos for life, or is a few years just fine? Waterproof and Nitrogen-purged is our minimum recommendation. This will give many years of service in its own right. Beyond this it comes down to the quality of the seals, the construction of the pop-up Eyecups (alloy is best), the quality of the focus mechanism, and the durability of the 'Skin', which is the rubber armour around the binos. Warranty varies from one year to unconditional lifetime warranty (usually 20 years) in the higher-end binos.


This is a somewhat more subjective measure: such as how they balance in your hand, the grip, and perhaps even the colour. You can’t beat getting your hands on a pair of binoculars, and that’s where we can help with many of the above binoculars in stock.


Binoculars to avoid

Binoculars with 'ruby coated' lenses, no stated prism type (usually inferior glass), and zoom binoculars (eg: 6 to 25x) magnification. The build quality will usually be poor, and the views terrible, especially at high zoom. These are the types you will usually see at your local discount store that seem like a bargain at under $50. However just like cheap telescopes are "worse than nothing at all" (what we like to call 'hobby killers'), bad binoculars are just the same.


Whatever you need in a pair of binoculars we are here to help you at Nightskysecrets. Call us on (07) 4000 4091, or call into our store at 321 Sheridan Street (Corner Smith) in Cairns North.

Ian MacLean, Night Sky Secrets


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