8x42 vs 8x56 Binoculars

After recently completing several reviews of 8x56 binoculars, and as a long-time owner of the Steiner Nighthunter 8x56 (known as the Steiner Shadowquest in North America), one of my all-time favourite instruments. I thought it would be worthwhile to take a closer look at how this larger objective lens size compares to the more common 8x42 configuration because by examining the key differences that result from simply increasing the lens size, I hope to help you decide which setup best suits your specific needs.

Objective Lens Size

8x42: The smaller 42mm objective lenses, mean that 8x42 binoculars are most likely to be more compact and generally lighter than 8x56 binos, making them easier to carry about and possibly handle when you are glassing.

8x56: Just as larger windows in your house let in more light, the larger 56mm objective lenses are able to gather (let in) more light than the 42mm ones can.

Thus if all else remains equal (quality of the glass, coatings, optical pathway optimization, build quality etc.) 8x56 binoculars will potentially seem to deliver brighter and possibly better quality images than equivalent level 8x42 binoculars.

This difference will not always be obvious or even observable, especially when ambient light conditions are good, but in low-light conditions such as dawn, dusk, or even at night most users will see more (a brighter image) with an 8x56 versus an 8x42.

The main reason for this difference is usually only obvious in low light and is all down to the relationship between the size of the pupils in your eyes and the size of the exit pupil on the binoculars:

Pupils & Exit Pupil Sizes

The exit pupil size of the binoculars and your own pupils’ size play a critical role in how bright and clear images appear

What is the Exit Pupil?

The exit pupil is the shaft of light that comes out of the eyepiece of binoculars. The diameter can usually be calculated by dividing the diameter of the objective lens by the magnification of the binocular.

So in this case, in 8x42 binoculars, the exit pupil is 5.25mm (42 ÷ 8), while in 8x56 binoculars, it’s 7mm (56 ÷ 8).

How the Exit Pupil Relates to Your Eye’s Pupil Size

Your eye’s pupil naturally adjusts in size depending on the light:

• In bright light, your pupils are likely going to constrict to around 2-3mm in diameter.
• In low light, they expand to let in more light, sometimes reaching 7mm or more, especially in younger people.

Because your eyes are flooded with light when using binoculars with exit pupils close to or larger than the size of your eye’s pupils, they can seem to produce a brighter image than a binocular which has exit pupils that are smaller than your pupils as they will be delivering less light than what you ideally need under those conditions.

Why a Larger Exit Pupil is Better in Low Light

So, in dim conditions, when your pupils are fully dilated, a larger exit pupil from binoculars will match or exceed the size of your eye’s pupil, allowing as much light as possible to enter your eyes. For instance:

• 8x42 binoculars with a 5.25mm exit pupil will perform very well in good and moderate light conditions, but in very low light, they may not fully match a fully dilated eye and so whilst they still perform ok (better than an 10x42 or a 8x32 for example), they will not be the ideal option.
• 8x56 binoculars with a 7mm exit pupil will better align with the eye’s maximum dilation, allowing them to provide a brighter and clearer image when ambient light is low and very low.

In essence, a larger exit pupil helps optimize the binoculars’ light-gathering capability, getting as much of the captured light to your eyes (light = information). So in low light, this enables you to see more detail and contrast.

8x42 binoculars: Produces a 5.25mm exit pupil (42mm/8). This size is well-suited for typical daylight viewing and also provides a reasonable experience in lower light.

8x56: Offers a larger 7mm exit pupil (56mm/8), which is optimal for low-light viewing and maximizes light transfer to your eyes. This is closer to the human eye’s maximum dilation in the dark, ideal for nighttime wildlife observation.

Field of View (FOV)

Generally, both 8x42 and 8x56 binoculars can offer a broad FOV, but the 8x42s tend to have a slight advantage because of their more compact optics and designs, often resulting in a wider view. This can be beneficial for scanning landscapes or tracking moving animals.

Ideal Uses & Conclusion

If you’re leaning towards flexibility, the 8x42 continues to be the go-to choice, but if you are after a superior low-light performance at the cost of a little size and weight, then all else being equal, the 8x56 will perform better for you.

• 8x42: Great for all-around birdwatching, hiking, and daytime use, providing a balanced experience with portability.
• 8x56: Optically performs excellently in all light conditions, but really do well in low-light situations, such as early morning, later afternoon, and early evening. Can also be a good option in thick forests or jungles. Therefore they are ideal in many birding and wildlife situations and are also a popular choice for binocular astronomy (wide-angle stargazing).

Top 8x56 Binocular Reviews on BBR

• Alpen Apex XP 8x56 Binoculars Review
• Bresser Pirsch ED 8x56 Binoculars Review
• Steiner Nighthunter 8x56 Binoculars Review

Top Performing 8x42 Binoculars on BBR

• Fujinon HC 8x42 Binoculars Review
• GPO Passion ED 8x42 Binoculars Review
• Hawke Frontier 8x42 ED X Binoculars Review
• Viking Osprey 8x42 Binoculars
• Vortex 8x42 Razor HD Review

Further Reading

• Does Age Affect Image Brightness in Binoculars?
• Exit Pupil – The Complete Guide
• What To Look For When Buying Binoculars
• How to Choose Between Binoculars
• 15x56 vs 18x56 Binoculars
• 7x50 vs 8x56 Binoculars for Astronomy & Daytime Surveillance
• 10x42 vs 10x50 Binoculars