Binocular Prisms – Why are they so Weird and Different

If you want to see distant objects clearly, you need to get a decent pair of binoculars. These devices can manipulate light, thanks to the uniqueness of binocular prism. The result of this is a clear image, regardless of how far it may be. But not all binoculars are similar. Manufacturers consider multiple factors during design. As a result, you can see different prices, sizes, and technology. So, if you want to buy binoculars, check out the best binocular reviews. In this write-up, I’ll explore the details of, particularly binoculars prisms.

How a Binoculars Work

Binoculars are devices that allow viewers to see distant images with clarity. Typically, they are two telescopes, laying side by side, and pointing in the same direction. This enables both eyes simultaneously to watch or view. The unique thing about binoculars is that they give users a three-dimensional (3D) images. Viewers usually get two views. However, if an object is near, the viewer receives the image from slightly different viewpoints. This produces a merged view with an impression of depth.

Now, binoculars have lenses and prisms.

The objective lenses are the lenses closest to the objects, while the eyepiece lenses are the ones close to the eye. Lenses play a vital role in enlarging the image to be brought to focus. All binoculars have these lenses.

The third element of binoculars is prisms. A prism is simply a solid glass piece, which functions as a mirror. However, it lacks the reflective backing of the mirror. Lights entering a prism won’t be reflected away if the striking surface at a too wide angle. Instead, the light rays reflect as if from a perfect mirror.

Binocular Prisms

Choosing binoculars will mean deciding between two kinds of prisms – Porro Prism vs. Roof Prism. That determines the type of binoculars.

Each prism comes with its advantages and disadvantages. So that can make it a little complicated to choose the right binoculars, more so if you are new to this field.

Whether you are looking for the best budget binoculars or just the best pair of binoculars, the kind of use you will put your binoculars is a considerable determinant.

So what exactly are Porro and roof prism?

Porro Prisms

This is a 19th-century technology by an Italian optician Ignazio Porro and is still in use today. However, the prisms have undergone some refinements to better the prisms. Porro prism binoculars have two prisms placed in a Z-shaped configuration. The configuration ensures that you get an erect image.

Typically, these binoculars send light captured by the binoculars’ objective lens through the prism pair horizontally. The horizontal movement between the two prisms acts bot as an invert and amplifier. As a result, sending magnified and upright, i.e., corrected image of what the viewer targets through the eyepiece lenses.


Porro Prisms


Unlike other binocular, Porro prism binoculars are wide. There is a decent noticeable separation between objective lenses. This results from an offset from the eyepieces. Thus, leading into a better depth sensation.

A notable advantage of Porro prism design is the folding of the optical path. It results in shorter binoculars’ physical length than the focal length of the objective. Typically, these binoculars have zigzag or offset shape, which makes it easy to differentiate from others.


Porro Prisms


However, these binocular look a little awkward, and they are heavier than other types. Besides, they are fragile. But they will give you a brighter 3D image with a large field of vision than others.

Above all, they are the best budget binoculars.

Roof Prisms

Achille Victor Emile Daubresse is the brains behind these binoculars. Typically, the roof prism binoculars are a pair of straight tube binoculars. Besides, they are streamlined and compact, and therefore much lighter. That means they are easy to carry around.

However, they have a sophisticated interior. The light path is an intricate and convoluted path reflecting the light from the objective to eyepiece lenses.

They use either of the following lenses:

Abbe-Koenig Prism

These groups of prisms invert an image by 180°. Roof prism is designed from two glass prisms optically cemented together, forming a symmetric, shallow Vee-shaped assembly. Light enters at a normal incidence and is internally reflected from a 30° sloped face.

Again,  the  “roof” section (i.e., two faces that meet at a 90°) reflects light at the prism’s bottom. Finally, the light is reflected from the opposite 30° face and exits, at normal incidence.


Roof Prisms

Schmidt-Pechan Prism

These binoculars have two prisms, which are separated by an air gap. Also, the prism inverts image by 180°. The unique thing is that light will bounce 6 times. As a result, pictures produced here aren’t crisp.

The entrance and exit beams don’t deviate the ray of light if centered on the optical axis. Ideally, the “roof” section of the upper prism flips the image laterally. This is due to the two total internal reflections. The reflections are in the horizontal plane from the roof surface.

These prisms are another budget option because they are cheaper to produce. Again, they are smaller and lighter.



Porro Prism vs. Roof Prism: Which should you choose?

These binoculars will give you different image qualities. The number of times light bounces determines the quality of images. Look, if light bounces many times, then images will be dimmer and degraded.

In Porro prism and Abbe-König prism, light bounces times. On the other hand, light bounces six times in Schmidt-Pechan prism, which means low-quality images. For the roof prisms to give good quality images, they need phase coatings.

However, roof prisms are small, which makes them more robust. Additionally, they are waterproof due to the fewer corners. Such features make them the best daytime hunting binoculars.

By contrast, the Porro prism binocular will give a wide field of view with clearer images. That makes them the best daytime and nighttime hunting binoculars. Besides, you can use them for stargazing and general outdoor activities except long-range sporting.

Final Thoughts

It depends on what you need. However, if you need high-end binoculars, then consider those packing Abbe-König prisms. These make the best birding binoculars. However, they come at a premium than others.

About the Author:

Hi, my name is Scott Jones. I’m a biologist from Maryland. I have an MSc in Systematic Biology and Ecology. I love to spend time in nature, watching birds and their habitats, and traveling to different continents to study wildlife. From my childhood, I would love to play with different optical scopes. I had a good collection of magnifying glasses and a cool pair of Russian made binoculars when I was in the 5th grade. With time I started to gradually build up more interest in binoculars. Then I collected several pairs of binoculars to quest my deep interest in optical scopes. Over time I learned how to determine the best binoculars pair. Then I decided to share what I knew with the world. Ever since I have borrowed a number of pairs and made some of the best reviews. I have developed blogs to share my knowledge and that’s how I got here. I am occasionally asked by binoculars suppliers to review their models. If you are willing to have reviews of your products under certain conditions please feel free to contact me at scotjones23 @

Leave A Comment