Welcome to Optics Trade debates. In each episode, we talk about a different topic and try to answer the most common questions we receive about it. Today, we are going to discuss two types of prisms that are used in binoculars.
Abbe Koenig prisms were named after the pair of inventors which worked on the development of prisms at Zeiss.
Both types of prisms mentioned are in the market minority because the most predominant type of prism used is the Schmidt Pechan roof prism.
Abbe Koenig prisms are a special sub-type of roof prisms.
Porro was the most common type of prism used in binoculars more than 20 years ago. There are less and less manufacturers that still produce Porro prism binoculars.
Porro prisms used to be used for everything, but in the last few years, the intended use changed a bit. One of its primary purposes is low-light observation, similar to Abbe Koenig. These kinds of binoculars are mostly used by European hunters who hunt in low-light situations. The other common category of use is in marine binoculars.
Abbe Koenig prisms are suitable only for low-light usage.
Porro prisms are usable in low-light and on water.
Most customers that want binoculars for low-light use look for binoculars with a 56mm objective lens and forget that the type of prism is also important. The amount of light that comes through the binoculars is usually greater with Abbe Koenig or Porro prisms than the Schmidt Pechan, even if the objective lens is smaller. For instance, a 42mm objective lens with Porro prisms usually gathers more light than a 56mm lens with Schmidt Pechan prisms.
High light transmission rates come with a high price tag. Binoculars that have a light transmission rate higher than 90% cost more than 1000€ if using Abbe Koenig prisms and up to 700€ if using Porro prisms.
Porro prism binoculars are big, heavy and are not ergonomic in comparison with Abbe Koenig prism binoculars. Porro binoculars cost less but are still dying out because of the lackluster user experience.
Both types of prisms can achieve the same resolution and the same field of view. Because of the greater distance between the objective lenses, Porro prism binoculars have a better depth of field.
The construction of Porro prism binoculars enables them to have a focusing system for both eyes.
Porro is currently more common than Abbe Koenig but in the feature, that trend is going to change. Despite that, Porro binoculars will stay on the market, especially in the marine segment because of the better waterproofness.
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Binoculars with Abbe Koenig prisms: https://www.optics-trade.eu/en/binoculars/shopby/prism_type-roof_abbe_koenig.html
Binoculars with Porro prisms: https://www.optics-trade.eu/en/binoculars/shopby/prism_type-porro.html