Optics Guide

The One Stop Nature Shop is proud to offer a wide range of binoculars from some of the industries best brands. With prices for an 8x42 binocular starting at just £59.00 there is something for everyone. But buying binoculars can be a very confusing experience. There is a lot of jargon that goes with them and many abbreviations which may mean absolutely nothing to you, this is where this guide will help.

The types of binocular 

Binoculars come in two different forms based on the prism assembly within them, Porro and Roof. 


As you can see from this diagram light passes through Porro and Roof prism binoculars in a different manner. The older style Porro prism can actually give a better depth of field compared to Roof prism binoculars but they are let down by being bigger, heavier and more difficult to hold. Being of a simpler construction Roof prism binoculars are easier to water and dust proof so these are features you will find pretty much every new binocular having. 

Bigger isn't always better 

So you've decided that you want either a Roof Prism or Porro Prism binocular. Now comes the biggest challenge you'll face, what size is best for me? 

The following are just some of the sizes that binoculars come in: 

  • 8x25
  • 10x25
  • 8x32
  • 10x32
  • 8x42
  • 10x42
  • 8x50
  • 8.5x50
  • 10x50
  • 12x50

etc, etc...

But what do these numbers mean?

The first number is always the magnification, this is the number which dictates how much the image is magnified when looking through these binoculars with a 10 times being more magnified than an 8 etc. 

The second number is your objective lens diameter, see the diagram above next to the small green arrows at the bottom of each binocular. The number is the millimetre measurement across the diameter of each lens. Bigger objective binoculars will in general be heavier than smaller ones but offer more light intake and therefore a brighter image when looking through. 

This brightness is also offset by the magnification. Using a simple equation we can see how bright a binocular is:

For example, a binocular with a 50mm objective and 10x magnification will have a "brightness" of 5 (50/10) where as a binocular with a 50mm objective and 8x magnification will have a "brightness" of 6.25, therefore it is brighter. This is offset by the quality of the optics but is useable as a general rule.

So which binocular is best for you? If you want something lightweight but with good brightness then some 8x42 and pretty much all 8x32 binoculars are your best bet. For ultimate compactness go for an 8x25. For extra brightness and magnification go for an 8.5x50 or 10x50, although you will have to consider the extra weight. 


So you've decided what type and size of binocular you want..then you see its got numerous letters and numbers on it which may aswell be a foreign language. 

Here is some of the abbreviations you may find on binoculars or on websites selling them, including this one: 

APO - An abbreviation of apochromatic. This lens system type corrects for any chromatic abberation, also known as colour fringing. 
BK-7 & BAK-4 Prisms - The two grades of glass. BK-7 are generally the cheaper optics and barium crown BAK-4 the pricier which give better sharpness.
ED, HD, HR - Extra-Low Dispersion, High Definition and High Resolution. Non standardised terms for glass quality, but highly variable with some non "HD" binoculars offering better optics than those with "HD" glass. 
Eye relief - Dictates the distance your eye should be from the eyepiece lens to optain optimum image quality. Spectacle wearers often benefit from longer eye relief.
Nitrogen filled - Waterproof binoculars filled with a dry, inert gas to prevent internal fogging. Argon is also used. 
Phase correction - Coatings applied to the prisms to give sharper images with better contrast and lower colour fringing. 

Still confused? 

If what we've typed here has left you perplexed then do not hesitate to contact us on 01485 211223 or by email: sales@onestopnature.co.uk .

Alternatively please pop into our shop at Dalegate market on the North Norfolk coast and we will be happy to advise on which binocular is best for you.