To distinguish different models of monoculars and binoculars, we can use two numbers: for example, 12×50 mm or 10×42 mm.
The first number (usually called magnification) indicates the zoom, or how many times the observed images appear enlarged. A 12×50 mm monocular will show us the objects (or subjects) 12 times closer, while a 10×42 mm will have 10 times zoom.
The second number after the x is in millimeters and indicates the diameter of the objective lens. A 12x50mm monocular will have a 50mm diameter objective lens, while a 10x42mm will have a 42mm lens.

FIELD OF VIEW
The field of view represents the area that you can observe with a monocular (or binoculars) at a distance of 1000 meters (1 km). The unit of measure can be both meters and degrees.
Let’s make an example.
In the technical description of our monocular, you can read Field of view 122M / 1000 M, which means that at a distance of 1 km, you will be able to observe a field of 120 meters.
You may happen to read “Visual angle”, also in this case we refer to the area that we can observe with the monocular but this time expressed in degrees. We can calculate it with a mathematical formula where the factor 17.5 represents the visual field in meters corresponding to a visual field of 1 °.
1000 m field of view = Visual angle in degree x 17,5
Visual angle in degree = 1000 m field of view / 17,5
Let’s come back to our example: 12×50 mm monocular with 120 M / 1000 M field of view and apply both formulas to calculate the field of view and the angle of view.
Field of view 1000 M = 6.85 x 17,5 = 120
Visual angle in degree = 120 / 17,5 = 6.8°
In a nutshell, the monocular has a field of view of 120M / 1000M and has 6.8 ° of field.
The width of the field of view is inversely proportional to the magnification: a 10x monocular will have a greater field of view compared to a 12x monocular.
Greater magnification = Wider field of view
TYPES OF LENS
The lenses used for monoculars and binoculars can be made in:
– Plastic. They are appreciated for their impact resistance during extreme sports. The images that appear in the eyes are of lower quality, consequently, the price is cheaper.
– Glass. They are mostly used in professional monoculars and binoculars. They produce quality images and the price is higher. The glass reflects the light that comes from the outside but this phenomenon is minimized through an anti-reflective treatment on the lens. Abbreviations are used to distinguish the different types of treatment for better light transmission and ensure clear images:
C (Coated): External lenses have been coated with a single layer of anti-reflection;
MC (Multi Coated): External lenses have been coated with multiple layers of anti-reflective treatment to ensure a better light transmission;
FC (Fully Coated): Both the prisms inside the monocular and the external lenses have been coated with a layer of anti-reflective treatment;
MFC (Multi Fully Coated): Both the prisms inside the monocular and the external lenses have been coated with fully multiple layers of anti-reflective treatment for better light transmission and greater protection of the lenses from water, humidity, scratches and accidental falls.
Multi-layer FC and MFC coatings are better compared to a single layer and this also increase the cost of the monocular and binoculars.