This is the second part of a multi-part series which aims to demistify the technical jargon surrounding binoculars. In our previous post regarding sports binoculars, we identified three technical details which binocular purchasers must consider. Those three details were Magnification, Aperture and Field of View.

Additional details to consider are Eye Relief, Close Focus, Exit Pupil and Prism Type.

Eye Relief

Eye Relief is important for eyeglass wearers. The reason why this is true, is that Eye Relief is the distance the binocular can be held away from the eyes and still allow one to see the entire Field of View.

Close Focus (Focusing Distance)

The Focusing Distance is defined as the shortest distance that the binocular can still provide a sharp image.

Exit Pupil

Hold up a binocular a few inches from your eyes. You will see in the eyepieces a small circle of light. The size of the circle of light is called the Exit Pupil. As Exit Pupils go up in size, the brightness increases.

Prism Type

The Prism Type (or system) of a binocular is what turns the upside down image to upright so you can see it correctly. There are two prism types;

• Roof Prism – with this system, the objective lenses line up fairly closely. This allows the lenses to line up with the eyepiece and results in a streamlined binocular.
• Porro Prism – with this system, the lenses are not lined up with each other and result in a wider binocular. Binoculars using a porrow prism system usually provide better depth perception and a wider field of view.