Why do binoculars use prisms?

A lot of people who don’t know about binoculars have a common question: why do binoculars use prisms?  To be sure, the use of prisms in binoculars is a must. In this article, we will learn about why do binoculars use prisms?

1. Type of prism  

A prism, or so-called vertical prism, turns the image upside down and faces the viewer as usual.  That was their original role.  There are two standard types of binoculars for these tools, namely roof prism, and Polo-prism binoculars.  

(1) Polo prism  

This is the most common type of prism used in binoculars, and its main function is not only to flip the image but also to redirect the binoculars according to their shape and size.  Due to the use of Porro prisms, binoculars can have large objective diameters and can be either large or small in size in the case that the objective is offset from the optical path of the eyepiece.  


(2) Roof prism  

The ridge prism serves only as an erector and folding light path, binoculars used to align the objective with the eyepiece.  The disadvantage of roof prism is that due to the loss of some light, the resulting image is not very bright.  This is mainly related to roof prism design, which makes Porro prism superior to roof prism.  

2. The difference between mirror and prism:  

In the past, binocular-makers used mirrors instead of prisms.  Due to their size and structure, using mirrors can result in heavier binoculars.  

Even the binoculars provide substandard image quality.  The mirror itself absorbs light and cannot transmit all the light it receives directly to the eyepiece.  Loss of light can cause the image to be dim and blurry.  

Prisms are internal reflective optical entities, so their light absorption rate is very low.  The prism reflects light at different angles and delivers the maximum amount of light to the eyepiece, so the image is brighter.  

3. Why do binoculars use prisms?  

The image produced by the objective lens is usually upside down or even upside down in some cases.  Imagine if our images were presented in the wrong direction, we would have to suffer headaches and eye pressure.  That’s where the binoculars’ prisms come in handy.  The prisms in binoculars come in pairs, each of which reflects light through the objective, corrects the image, and further sends it to the eyepiece, where you can see the enlarged image, clear and unflipped.  


If there is no prism in the binoculars, the image will be reversed.  Have you ever tried or tried to use convex and concave lenses to align them in front of your eyes?  You get magnification, but the image is inverted.  The prisms are assembled into the binoculars at specific angles to allow light to be reflected as much as possible.  Each binoculars has a different prism position, depending on the shape and length of the fuselage.  

If you look at old binoculars, they were bulky and difficult to carry because they used mirrors inside instead of prisms.  Modern binoculars are more compact and user-friendly thanks to prisms.  The prism folds the light path, making the binoculars smaller.  This is the second advantage of binoculars using prisms.  

Binoculars magnify what we see, making the world we see through them seem larger.  The type of binoculars is determined by the type of prism they have.  

Prisms are a necessary part of binoculars to turn images in the right way and are small enough to allow them to be held in the hand due to their short light path.  Porro or Ridge prism, your choice.  The above article will help you buy binoculars in the future.  

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