Porro Prism vs Roof Prism Binoculars: Detailed Comparison 2023

By Richard

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When it comes to choosing a set of binoculars, one of the first decisions you’ll need to make is whether to go with roof prism or Porro prism binoculars. But what are the differences between these two types? And which is better for your needs? In this article, we will take a closer look at both roof and Porro prism binoculars and compare their features side-by-side. By the end, you should have a good understanding of which type of binoculars is right for you.

Related article: Eye relief of Binoculars

What is Prism?

Let’s start from the basic level and learn about prism. In short, it is a piece of glass that is used to reflect light in a particular direction. In other words

“A prism is a transparent optical element with flat, polished surfaces that refract light. The typical shape of a prism is that of a triangular pyramid”

There are two main types of prisms used in binoculars which are listed below;

  1. Roof prisms
  2. Porro prisms

Roof prism binoculars are designed with prisms aligned in a straight line, while Porro prism binoculars have the prisms offset from each other. This offset design is what gives Porro prism binoculars. This is probably the easiest and simplest introduction that can be possible for prism. Here comes the detail

Roof Prism Binoculars

A roof prism is a modern type that is being used in almost all modern optical instruments. Roof prism binoculars are also known as ” streamlined ” or ” compact ” binoculars because of their slim design. Roof prism binoculars are usually lighter than Porro prism binoculars, and they often have a rubber covering to make them more comfortable and easier to grip.

Porro Prism Binoculars

Porro prisms are an old-fashioned prism type that was developed in the 19th century by Ignazio Porro. This prism type has been used in a variety of optical instruments for a long period of time until the roof prism was developed.  

Binoculars containing Porro prisms tend to be bulkier than roof prism binoculars. They get their name from the Porro prism, which is the type of prism used in this design. Porro prism binoculars usually have a wider field of view than roof prism binoculars, and they are often less expensive.

Roof Prism Binoculars
  • Modern
  • Streamlined
  • Compact
  • Lightweight
  • More expensive
  • More magnification strength
  • Come with a dielectric coating
  • Images produced by Roof prism are less stereoscopic.
  • Show solid resistance against water and fog
Porro Prism Binoculars
  • Old fashioned
  • Zid-zag shaped
  • Bigger sized
  • Heavier
  • Less expensive
  • Less magnifiation power as quality
  • No coating at all
  • Images of Porro prism are more stereoscopic
  • Comparatively resistive again water and fog

How do prisms work in Binoculars?

The working of a prism in binoculars involves the use of refraction to split light. Prisms are placed at strategic locations inside the body of a pair of binoculars so that they can redirect incoming light by 90 degrees. This process enables the creation of an image that is much brighter than could be created using a single lens.

The light enters the binoculars through an objective lens. In previous articles on what the numbers in binoculars mean, we have already explained that objective lenses function to capture light. The captured light goes to the prism. 

The prisms placed in the binoculars start doing the work as they reflect the incoming light rays from the objective lens. As a result of reflection, the creation and amplification of images take place. The prism inverts the image. The inverted and amplified image is sent to the ocular lens where the user can observe a clear, brighter, and perfectly oriented image.

How does the Porro prism work?

Porro prisms have one flat surface that is perpendicular to the other. This creates a wedge shape, which allows for light to enter at one end and exit through the other with minimal refraction. This also means that Porro prisms only need to be used once before light emerges out the other side.

How does Roof Prism work?

Roof prisms, on the other hand, have two flat surfaces that are parallel to each other. This creates a V-shape, which means that light has to pass through the prism twice in order to exit. However, roof prisms can be used multiple times before light exits, which makes them more versatile.

Differnce between Porro prism and Roof prism
Image Credit: Optics Mag

Roof prism vs Porro prism: Which one should you buy?

Roof prisms and Porro prisms are two different types of prismatic structures that are used in binoculars and other optical devices. So, which one should you buy? To help you decide, let’s explore some of the key differences between these two types.

A roof prism is constructed with two right-angle prisms that are positioned next to each other, while a Porro prism has a single right-angle prism sandwiched between two 45-degree angled prisms.

This difference in construction results in several other differences in performance. For example, roof prisms offer a reduced length and width, making them ideal for compact binoculars. These prisms also transmit light more efficiently than Porro prisms, which means a brighter image with less eye strain. 

Porro prisms, on the other hand, offer a wider field of view than roof prisms and are often less expensive to produce. However, due to their construction, Porro prism binoculars are larger and heavier than roof prism units, which means that they are not ideal for compact binoculars.

Which one should you buy?

Ultimately the choice between roof prisms and Porro prisms comes down to personal preference. You may want to consider factors like light transmission efficiency, portability, and field of view when deciding which type is best for your needs

Roof being modern technology helps in many ways. It gives you better image quality while making your binoculars lightweight. Their streamlined design and compact size will ease your carrying efforts. But their prices are higher than Porro prism binoculars.  If budgie is not your concern you should always look for roof prism binoculars.

If your budget is a serious concern and cannot afford to spend more on your optics then Porro prism should be your choice. The binoculars with Porro prism will be heavier, and less powerful as well as inexpensive. Along with affordable pricing, Porro prism binoculars provide the widest field of view possible.

BAK-4 and BK-7 Prism Glass: Which one is best?

BAK-4 and BK-7 are both types of prism glass that are commonly used in binoculars and monoculars.  BAK-4 has a higher refractive index which makes it able to enhance the image quality by increasing the transmission of light. This makes BAK-4 a more suitable choice for applications that require high levels of detail, such as bird watching or wildlife viewing.

The image quality with BK-7 material gets compromised. But there is a major pricing difference between these two. BAK-4 is also more expensive than BK-7, and in some cases, the difference in image quality may not justify the additional cost.  BAK-4. BK-7 is a more affordable option that many optics users prefer.  If you want quality, we recommend you some extra to avail BAK-4 glass type.


No doubt that both roof and Porro prism binoculars are being sold and bought as both have good marketing. Those who are optics enthusiasts and love spending on their outdoor gadgets buy roof prism binoculars. People with limited budgets go for Porro prism binoculars. Both are good in their ways.

We personally use roof prism binoculars and we never got disappointed by their performances. In fact, porro prism binoculars are not near the roof prism binoculars in any way. Spending a few extra bucks will buy you top-notch and perfectly performing-binoculars. 

Frequently Asked Questions

What is the difference between a roof prism and a Porro prism?

A roof prism is typically thinner and lighter than a Porro prism, making it more compact and easier to carry. Roof prisms also tend to have better optical quality, due to their simpler construction. However, they are more expensive than Porro prisms. On the other hand, Porro prisms are less expensive than roof prisms and are also easier to manufacture, which makes them more widely available. They also offer a wider field of view than roof prisms.

What is a roof prism?

A roof prism is a type of optical prism that is often used in binoculars and monoculars. It is typically wedge-shaped and has two reflecting surfaces that are perpendicular to each other.

What is a Porro prism?

A Porro prism is a type of optical prism that is often used in binoculars. It is typically rectangular in shape and has two reflecting surfaces that are parallel to each other.

What are the advantages of a roof prism?

The main advantage of a roof prism is that it allows for a more compact design. Roof prisms also have the potential to provide better image quality than Porro prisms.

What are the advantages of a Porro prism?

The main advantage of a Porro prism is that it typically provides a wider field of view than a roof prism. Porro prisms also tend to be less expensive than roof prisms.

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