What are the roof prism binoculars?

Roof prism binoculars have all the three things namely the eye piece, the objective lens and the prisms all in one straight line. This helped as then the design of the roof prism binoculars was more elegant and in general there would be no such thing as the zig-zag pattern of the Porro prism binoculars.

It is easier said than done. The design was more complex internally for the roof prism binoculars and hence it was tough to manufacture. That is why the low -end binos will always be those if Porro prism system and the high -end will be roof prism binoculars.

Roof prism binoculars vs. Porro prism binoculars

Roof prism binoculars are much better looking than the Porro prism binoculars as far the design is concerned.

On the price front the Porro prism binoculars are much better than the roof prism binoculars.

In terms of light efficiency the Porro prism binoculars are much better than the roof prism ones. However now with the phase-coatings being used on the prism glass the roof prism binoculars have become equally good compared to the Porro prism binoculars

What are prisms? 

If you only used an eyepiece and then used the objective lens to see the image of the object that you are looking at then you will see the image inverted that is upside down as well as you will have the image which is reversed left for right. To correct that prisms are used in between the eyepiece and the objective lens. The prisms are used for bending the light which corrects the inverted image.

There are two types of prism systems that are used in the binoculars of today. These are the Porro prism systems and the roof prism systems. In fact there are three types and the third system is the reversed Porro prism binoculars.

The glass with which these prisms are made is known as BAK-4. Details about this later in the subsequent posts.

What are Porro prism binoculars?

Just to give you an idea look at the image below of the Porro prism below. Porro prism binos were popular in the 1960′s but now the more popular are the roof prism binoculars. They have an offset zig-zag design. This design was introduced because the light in the case of Porro prism binoculars travels in a zig-zag pattern and hence the eye piece, the prisms and the objective lens could not be in the same straight line.

With roof prisms that problem was resolved though not easily and hence generally you will see that roof prism binos are more costly than the Porro prism binos.

Porro prism binoculars are more efficient than the roof prism ones as they have better simpler mechanism to control the light.

Reversed Porro prism binoculars are very compact and can easily be the best for very compact travelling binos.

Of late however the roof prism binoculars have easily made great advances in their light management techniques and hence now they are at par with the Porro prism binoculars for light efficiency and optical experience. The way it has been achieved is via the use of the Phased coatings.