10x42 vs 10x50 Binoculars

BBR Video Version of this Article on 10x42 vs 10x50 Binoculars

Having recently completed testing and reviewing the excellent Kite Lynx HD+ 10x50 binoculars, it reminded me how for some uses, this configuration makes the ideal solution and how for some users it can certainly make a better choice than the more commonly selected 10x42 combination. 

So in this article, I am going to go over the main differences in both the physical aspects and the optical performance that you can expect to get between a 10x42 binocular and a 10x50 one of similar quality.

In this way, by the end of this article, you will be able to decide which configuration is best suited for your specific requirements and preferences. 

To start with, if you are not sure, please take a moment to go over this article on What the Numbers Mean on a Binocular

42mm Lenses (top) vs 50mm Lenses (bottom)

Physical Differences


It stands to reason that in order to accommodate the larger objective lenses, the barrels on a 10x50 binocular need to be larger as well. This has a bearing on the instruments overall dimensions and thus 10x50 binoculars are larger than 10x42s. 

How Much Larger?
50mm lenses are 8mm bigger in diameter than 42mm ones and thus the ends of the barrels where the objective lenses are set, reflect this difference by about the same amount. As you move down towards the ocular lenses, they taper down in size as most 10x50 binoculars will incorporate the same eyepieces as that of the 42mm versions. 

10x50 Versus 10x42 Binoculars

10x50 binoculars also tend to be a little longer than their 42mm counterparts. However once again, the difference here is fairly minimal (usually under 10mm).

Therefore and as you can see from the photo below the overall difference in size between a 10x42 binocular and a 10x50 one is really not that great. Indeed I would go as far as to say that most users would not guess the difference if you were to swap their binoculars without them knowing. 

Size comparison between the Kite Lynx HD+ 10x50 Binoculars and the 10x42 Bresser Condor Binocular

Size comparison between the Kite Lynx HD+ 10x50 Binoculars on the left and the 10x42 Bresser Condor Binoculars on the right.


Glass is a reasonably heavy material and thus once again, the extra glass needed to make the lenses and the extra material for the slightly larger body results in a 10x50 binocular being slightly heavier versus a 10x42 model using the same level of materials. 

Note: If maintaining a low weight is a priority of yours, you can do things like look for a binocular that uses a polycarbonate chassis and plastic components like the focus wheel instead of metal ones, which can make an appreciable difference. 

Optical Differences

Just as larger windows in your house are able to let in more light, the larger surface area of 50mm lenses means that they have the potential to “capture” more light than 42mm ones. 

Note: Just like the quality of glass used to make the windows in your house, instruments using poor quality optics and coatings will not perform as well as higher quality ones and thus I am assuming that we are comparing binoculars of a very similar level. 

More light means more information and thus if all else is equal, there is the potential for brighter, better quality views through 10x50 binoculars versus 10x42 binoculars. 

However just being able to capture more light does not automatically make for a brighter, better quality view. As much of the light as possible needs to get transmitted to your eyes and this is where differing levels of glass, optical coatings and build quality do play an important part.

On top of this, during the day in normal light conditions a good quality 10x42 binocular is able to capture and transmit enough light to your eyes for you to perceive a bright, high-quality image and thus under these conditions you most likely will not be able to differentiate the brightness between the views of an equal quality 10x42 and 10x50 binocular. 

However, it is in situations where the light level is not optimal, like just before sunrise, at sunset or even in a thickly wooded forest, where the extra capability that the larger instrument comes to the fore and you begin to notice the difference in the image. 

You can clearly see the larger exit pupil in the ocular lens on the 10x50 on the bottom versus the 10x42 on the top

This can be explained by the size of the shaft of light exiting the ocular lenses (exit pupil) and the size of the pupils in your eyes.

  • 10x42 binoculars produce a 4.2mm exit pupil (42/10)
  • 10x50 binoculars produce a 5mm exit pupil (50/10)

When there is plenty of light, your pupils constrict to a size smaller than both the exit pupil on a 10x50 and a 10x42 and thus there is more than enough light for you to perceive a bright view.

As the conditions get dimmer, your pupils begin to expand until, in very low light conditions, the pupils in some people (it varies) can reach 7mm in diameter. Thus the amount of light your eyes are receiving is sub-optimal and therefore the 10x50 will look to you to produce a brighter, better quality view.

Incidentally, 8x42 binoculars, which are generally considered the best all-rounders have exit pupils of around 5.25mm and thus as you can see, the 10x50mm configuration comes very close to matching this. 

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

Other Advantages

A larger Exit Pupil also makes it easier for you to line your eyes up with the light exiting the eyepieces and thus a 10x50 binocular is simpler to use because it is easier to achieve an image without black rings on the edges of the view.

Price Differences

10x50 binoculars are usually a little more expensive than the 10x42 alternative from the in the same series from the same manufacturer. So why is this?

Whilst it is true that they need more glass to make the larger lenses and a little more material to make the larger bodies, so I guess this has a bearing on the final cost, but to be honest this is not really the reason for the price difference. 

Economies of Scale
The main reason that 10x42 binoculars are cheaper than 10x50’s is down to the economies of scale: Because the 10x42 configuration is so popular and added to this 10x42 binoculars will share the same chassis and many of the same components and optical parts as the even more popular 8x42 model in the same series, it means that a manufacturer can make  or order in many more of these parts than the more specialized ones needed to make a 10x50 binocular. 

How Much More Expensive?
This depends on the brand, what price range of binoculars you are looking at and where in the world you are shopping, but in general, I have found that the price difference tends to be between 5% to 20% more for a 10x50 compared to the equivalent 10x42.

So, for example, the Kite Lynx HD+ 10x50 binoculars cost around $1019 / £770 / €770, whilst the 10x42 model will set you back about $980 / £739 / €736. 


Unless you specifically need your instrument to be as “compact” and lightweight as possible, for me the size and weight penalty of a 10x50 versus a 10x42 is really nothing to be concerned about. Indeed if you really are looking for a smaller instrument, you may wish to consider a mid-sized 10x32 instead. Although as you will appreciate here the light gathering ability, exit pupil and thus all the associated issues in terms of low light performance that we have gone over will be even more exaggerated, so you need to keep this in mind. 

Optical Performance
In normal daylight conditions and using the same level of instrument, you really can’t notice a difference between the two in terms of the image brightness and quality, but in low light, there is no doubting that I would much prefer to have a 10x50 binocular in my hands over the 10x42 model. 

In terms of cost, this will be a personal decision based on how much you value the extra money you either keep in your pocket or spend versus the associated benefits and drawbacks of choosing a pair of 10x42 vs 10x50 binoculars.

10x42 or 10x50, Which is the Best?

As with just about any binocular configuration, there is no single best option, rather which one is best for your specific requirements and preferences:

10x42 is best for daytime use in normal to good light conditions and you gain the benefits of a lower costing and fractionally smaller instrument.

10x50 is best if as well as during the day, you also sometimes use your binoculars in low light and want an image brightness that is similar to that of an 8x42, but also the added image detail that a 10x power gives you and are willing to pay a little more as well as add a few grams and millimeters to the instrument. 

Further Reading & Related Info

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