15x56 vs 18x56 Binoculars

Next in the BinoWars Series, I will be closely analyzing the relative strengths and weaknesses between 15x56 and 18x56 binoculars to discover which is best for uses like general long-distance observation down here on earth and astronomy.

Video Version: 15x56 vs 18x56 Binoculars

Based on the number of visitors, one of the most popular sections on BBR is my guide on how to choose the Best High Powered, Long Distance Viewing Binoculars taking into account your specific needs and requirements and so I thought it was high time to delve a little deeper and take the two configurations where I get the most questions in regards to being unsure of which one is best under which circumstances.

So below I cover the main physical and optical performance differences that you will most likely get between similar quality 15x56 and 18x56 binoculars:

As always, if you are unsure, please first take a look at What the Numbers Mean on a Binocular

Physical Differences

Assuming that you are comparing the same type of instrument (roof & Porro prism) then because they both use the same diameter objective lenses, both 15x56 and 18x56 binoculars will have similar dimensions.

Indeed if you take two examples from the same manufacturer and series, say for example the outstanding Maven B5 18x56 binoculars and the 15x56 version, they use exactly the same housing and exterior armor and thus have identical dimensions: 8.2in (20.8cm) x 6.1in (15.5cm) x 2.5in (6.4cm).

However, just be aware that instruments from different manufacturers and especially those with different designs can vary quite a bit in size and is worth keeping an eye on if this is important to you.

For example, take a look at the image below. Would you guess that all three use the same size 56mm lenses?

Three 56mm Binoculars

Here the difference is size is largely down to the design of prism used inside them: The  Bresser Pirsch ED 8x56 on the left has the most compact and widely used Schmidt-Pechan roof prisms, the Maven B5 18x56 uses the longer but more “efficient” Abbe-Koenig prisms, whilst the  Steiner Nighthunter 8x56 on the right uses the very efficient, but wider Porro Prisms.

Likewise, apart from tiny changes in the thickness of the ocular lenses because of the different magnifications, the weights between similar level 18x56 vs 15x56 binoculars are not worth worrying about.

Note however that higher-end instruments will have features like aluminum or magnesium housings and components, that are usually better, but also heavier than the plastic polycarbonate equivalents used on most mid and lower-tier instruments.

Objective Lens Covers on the Steiner HX 15x56 Binoculars

Large 56mm lenses on the Steiner HX 15x56 Binoculars.

Optical Differences

15x vs 18x Magnification

As a binoculars main point of being is to magnify an image and thus hopefully provide you with a better/more detailed view of distant objects, it is perfectly reasonable to assume that the more powerful a binocular is, the better.

However, the truth is, this is most certainly not always the case, as higher powers also bring with them a number of drawbacks that are very important to understand:

Image Detail at Long Distances
In theory, the higher 18x power on the 18x56 will enable you to observe more image detail or “see more” at longer distances than with an equal level 15x56 binocular.

Objective Lenses on the Maven B.5 18x56 Binoculars

Maven B.5 18x56 Binoculars mounted onto a tripod

Image Shake
When looking through any pair of binoculars, every tiny movement that you make gets amplified by the magnification, which you see as image shake in the view.

Thus, the higher the magnification, the more image shake you get with the same amount of movement.

If you have relitively steady hands, the general advice is to use some sort of stabilization (monopod, tripod or stabilized binoculars) for any magnification greater than about 12x.

Although, I have found that in some situations I can use a 15x and even an 18x binocular from the hands, but only for short periods of time. But having said that there is no doubt that you get a much better view and are able to better observe the details (which is the main point of high powers) once the binocular is perfectly stable.

This if we assume that you will be stabilizing the binoculars, then image shake between the two is a non-issue. However, from the hands, it is noticeable to me how much easier it is to keep a 15x56 more steady than an 18x56 binocular.

18x vs 15x magnification & Field of View
Image Detail vs Field of View: 18x vs 15x

Field of View & Seeing the Big Picture
I use versions of this image above often on BBR because I think it clearly illustrates how a higher magnification brings you closer into the action for a more detailed, “zoomed-in” view, but at the same time you also lose out on what else is happening all around the area.

At closer ranges this can be a major problem, especially if you are trying to quickly locate and then follow a small, fast moving object or animal.

At longer distances, a narrower field of view is generally not as much of a problem, but a narrow field of view still makes it more difficult if you are scanning large areas searching for something.

So, whilst both the 15x56 and the 18x56 configurations are essentially designed for long-distance observation, you still need to factor into your decision how far into the distance you are generally going to look and how often you will be using them at closer ranges, especially if following fast and/or small objects are concerned.

Image Brightness

Assuming that the quality of the glass and the coatings are equal and because they both have the same size 56mm objective lenses, it is true that both 15x56 and 18x56 binoculars have the same capabilities when it comes to “capturing” and directing light into the binocular and thus you may assume that they would both deliver an image of equal brightness. However, this is not always the case:

Available Ambient Light
In good and even average to quite poor light conditions, the difference in image brightness between an 18x56 vs 15x56 binocular of equal quality is in my experience not at all an issue.

In fact, to my eyes, the view through a high-end 18x56 binocular like the Maven B5 18x56 looks as bright as that of an equal level 10x or 12x56 when there is a reasonably good amount of light and thus under these conditions really is not something to worry about.

However, once the ambient light levels drop, like that you would experience before sunrise, or at or just after sunset, then you start to notice some differences.

Exit Pupil Size (left to right): Steiner 8x56 Nighthunter/Shadowquest (7mm) vs Steiner 15x56 HX (3.7mm) vs Maven 18x56 B5 (3.1mm)

Exit Pupil Size & Your Pupils
This can be explained by the relationship between the size of the pupils in your eyes and the size of the shafts of light exiting the ocular lenses (exit pupil) of the binocular:

  • 15x56 binoculars create a 3.7mm exit pupil (56/15)
  • 18x56 binoculars create a 3.1mm exit pupil (56/18)

The pupils of your eyes change in size depending on how much light is available. During the day and out in the open, most people’s pupils will probably be less than 4mm in diameter and thus both 18x56 and 15x56 binoculars are able to pass on enough light for you to perceive a bright image.

Thus under these conditions, it is often impossible to notice a difference in brightness between these two and indeed many other configurations of equal quality.

Low Light Performance
However, when in low light, your pupils can expand to about 7mm in diameter to let in more light.

Under these conditions, binoculars with larger exit pupils (but all of the same quality), most certainly have the advantage and which is partly why an instrument like the Steiner Nighthunter 8x56 with its massive 7mm exit pupil and excellent light transmission levels is so good in very low light conditions.

More info on all of this can be found in my complete guide to the Exit Pupil

3.7mm and 3.1mm
Going back to this example of 15x56 vs 18x56 binoculars, the difference between 3.7mm and 3.1mm is not massive and so whilst I would not describe either as being particularly good in low light, the 15x56 has an advantage, but it is only slight.

So I think here rather than worrying too much about which is best in low light, if you do find you often use your optics in very bad light, you should rather be thinking of choosing a binocular like an 8x56 or 10x56.

However, if you only occasionally need them in lower light, then you may lean towards the 15x56 over the 18x56.

What About Astronomy?

Whilst a large exit pupil is obviously an advantage at night, I think that when it comes to astronomy, because you are looking at bright shiny objects like stars and especially the moon, your pupils actually reduce in size (I think) and thus the exit pupil size is not as important as you would imagine and rather it is more important to have large objective lenses and good quality optics that can firstly collect as much light as possible and then transmit as much of it through the instrument.

This is my theory anyway!
I say this because I have honestly been blown away by the views that I am able to get of the moon through the Maven B5 18x56 – the amount of detail of the craters that you can see when compared to a 7x50 or 8x56 is impressive and there is so much less haze and color fringing than when compared to lower quality instruments.

However, on the flip side, you don’t get the wide views of the night sky and if your main interest is astronomy, then I would still suggest getting a binocular with larger exit pupils specifically designed for stargazing.

Swarovski SLC 15x56 HD Binoculars

Swarovski SLC 15x56 HD Binoculars

Price Difference

In general, higher-powered binoculars tend to be a little more expensive than the equivalent model but with a lower magnification from the same series and manufacturer.

In the case of something like an 10x42 vs a 15x56 for example, this difference in price is easily understandable as larger binoculars require more material to make and have larger lenses that use more glass.

However, as we have already seen, 15x56 binoculars and 18x56 binoculars are pretty much the same size and often use exactly the same bodies and components, so why the discrepancy?

In the case of 8x42 vs 10x42 binoculars, for example, this is down to the economies of scale, as manufacturers will usually sell far more of the less powerful models than the more extreme ones and thus are able to make more lenses, more efficiently.

I assume this is also the case with this example as 18x56 binoculars tend to cost more than the 15x56 version.

Where to Buy & Price Comparisons


15x56 or 18x56 Binoculars, Which Are Best?

Once again, when it comes to different configurations between binoculars, there is no smoking gun answer as to “which is best?”. It really does depends on your personal requirements and how you will usually be using the instrument:

15x56 Binoculars will generally have a wider view and a very slightly better low light performance than the equivalent 18x56 and are fractionally easier to use from the hands if needed.

18x56 Binoculars, on the other hand, get you even close to the action and bring you even more image detail and are a great option for those who want to get close to the detail that you can achieve with a spotting scope, but maintain the more immersive experience that you get from using two eyes.

Neither configuration is particularly good in very low light, at close range, or if you are looking for a small lightweight binocular to travel with!

Recommended 56mm Binos

Low Light, Wider Views:

Further Reading & Related Info


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