Even though binoculars are a common tool used for many different occasions, the actual dynamics of binocular optics and how binoculars work is understood very little by those who actually use them.  Binoculars seem like quite confusing contraptions at first, but once you have an understanding about binocular optics and how binoculars work, you will find they are quite simple.

Binocular Optics and How They work

Zeiss Binoculars from the early 1900’s. Zeiss is still a huge name in optics, well over 100 years later. Follow the link at the end of this article to see Zeiss’ newest optic models, as well as the other top players of the binocular optic industry

Binoculars are essentially two telescopes placed side by side to give a viewer a more efficient view by using both eyes.  There is one catch though.  Telescopes are used for viewing large objects at long distances, mostly for astronomy, and actually magnify the object upside down.  Typically space objects look the same regardless of them being upside down, so it doesn’t really matter.  This is not the case when looking at terrestrial objects as they are needed to be right side up to view the image correctly and efficiently.  Therefore, telescopes had to be modified to be used as binoculars.

There are several components that go into binocular optics.  Here is a list of the components and then an explanation on how binoculars work.

  • Objective lens
  • Prisms
  • Eyepiece
  • Focus
  • Lens Coatings

Objective Lens:

Binocular Optics and How Binoculars Work

The objective lens is the one you can see in this picture.

The objective lens is the biggest lens that is closest to the object being magnified.  The object of this lens is to gather the light and magnify.  This is similar to using a magnifying glass to magnify the intensity of the sun to make extreme heat.  Both binoculars and magnifying glasses use a convex lens, also called a converging lens, which brings distant light rays into a focus.  The image that is displayed is then picked up by the next lens and magnified further.  Of course, there are steps in between this process that are used to produce a higher quality image.  The bigger the objective lens, the more light it will capture, thus giving a higher quality image, but this also results in a larger overall size of the binoculars.  Quality can also play a big part in image sharpness; the higher the quality of objective lens, the better the end image will be.


Binocular Optics

Porro Prism Diagram

The prisms are the part of binocular optics that flip the image.  Before the image gets to the prisms, it is upside down.  This is similar to if you use a magnifying glass, the image will be upside down at a certain point.

Prisms are basically wedge shaped pieces of glass and binoculars have two of them.  The image bounces off the first prism correcting the image by 90 degrees and is then reflected to the next one which flips it the rest of the way and send the image toward the eyepiece

There are two types of Prisms that are most commonly used in binocular optics.

  • Porro Prisms

    Binocular Otics and How Binoculars Work

    Roof Prism Diagram

These are the prisms used in the original binoculars of the 19th century, and are still used today.  They are used by bouncing the light at 90 degree angles and require quite a bit of space, thus making for overall larger binoculars.

  • Roof Prisms

Uses prisms to bounce and rotate the image with angles of more and less than 90 degrees.  Roof prisms are more in line with each other than porro prisms, resulting in a more compact design.   They are used in most expensive and compact models.

How Binoculars Work

Diagram showing the difference in Roof Prism and Porro Prism Binoculars.


Once the image is right side up, it is then picked up by the eyepiece lens and magnified even further giving you the image that ultimately hits your eye.  The eyepiece is the lens that is closest to your eyes.


Binocluar Optics and How They Work

Standard Binocular Diagram

When the image gets to your eye, there may be some focusing needed to make the image sharp and clear.  To focus a binocular, a dial is turned that adjusts the distance between the ocular lenses (the objective and eyepiece lens).  The exact point at which the object is focused will depend on the actual distance to the object, thus needing to be adjusted with each use depending on the situation.

Lens Coatings:

Since binocular optics have so many components to go through, lens coatings have been implemented to give off an even sharper image.  These coatings not only protect the ocular lenses, but improve the image by reducing glare and fogging, apply phase correction for roof prisms models, and make the lenses easier to clean and repel liquids.

Best Binoculars for You

Here is a picture of perhaps the best binoculars ever made. Swarovski is known for manufacturing some of the best optics in the world. Click on the website link at the bottom of this page to see how much these binoculars cost.


Ready to Pick Out Binoculars That are Best For You?

This is a just a quick explanation of Binocular Optics and how binoculars work.  There is much more in depth information out there, and if you would like to know more click the link above.  If you are in the market to buy binoculars, the best advice I can offer you is to go with the best you can afford because you get what you pay for.  To view the best binoculars ordered by price range, please go to my blog here: http://www.BestforHunting.com.

Keywords: binocular optics, how binoculars work, binoculars, optics, roof prisms, porro prisms

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