Dawn observation with Solognac binoculars

HUNTING BINOCULARS

Everything you need to know about how they work.

Light transmission percentage is a fundamental criterion of good binoculars. But how does this transmission occur? What coatings do we apply to our models? What key factors should you know?

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BINOCULAR BASICS

To fully understand our design choices, it is essential to focus on how binoculars function. To start, we must cover a fundamental optical principle: the correlation between a binocular's format and its brightness. Binoculars are defined by two numbers. For example, 10x42. The first number, 10, is the magnification. The second, 42, is the objective lens diameter in millimetres. Dividing the two gives a value in millimetres. For instance, 42/10 equals 4.2mm. This is known as the exit pupil. Practically speaking, the exit pupil corresponds to the beam of light leaving the eyepiece to reach your eye. For a 10x25 binocular, the exit pupil is 2.5mm. On an 8x56, the exit pupil is 7mm. This detail is crucial, and you will see why.

Diagram explaining human pupil dilation according to ambient lighting

THE EYE, A COMPLEX ORGAN

Let's focus on how the human eye works. The eye consists of rods and cones. Rods are photoreceptors transmitting luminance sensations: white, black, or grey. Cones handle colour perception. If the eye receives minimal light, we perceive grey tones. If it receives abundant light, we perceive all the colour shades available. The exit pupil's role is ensuring the light beam leaving the binocular fully covers your eye's pupil.

Where it grows complex is that the eye's pupil contracts and dilates based on ambient light. In daylight, the pupil measures 2-3mm in diameter; in dark conditions, it reaches 7-8mm. Age also plays a role: at 18, a dilated pupil reaches 8mm; between 18 and 30, it averages 6-7mm; between 30 and 50, it is 5-6mm; and at 60-70, it is closer to 5mm.

Another key point: parents observing nature with children often note different viewing experiences. Children's pupils dilate further. A 50-year-old adult may enjoy a bright view through binoculars, whereas a child might perceive a grey or flat image. Consequently, depending on age and lighting conditions, every binocular format serves a specific purpose.

HOW LIGHT TRAVELS THROUGH YOUR BINOCULARS

The second key optical principle concerns how light travels through binoculars. Looking at this X-ray visual of binoculars, the objective lens sits at the bottom. Light passes through the objective, then through the focus lens (used for sharpness), through the prism, and finally through the eyepiece lenses. Light travels in a straight line, but encounters obstacles like optical components. At each surface contact, light can be absorbed, scattered, reflected, or refracted. Passing through 6, 7, or 8 optical interfaces, light loses around 5% transmission per surface. Without coatings, light entering the objective at 100% exits the eyepiece at roughly 60%, resulting in low contrast and a dull, dark image. Binocular design aims precisely at maximizing sharpness and image quality.

Close-up on the coloured reflection of a multi-coated lens (FBMC)

HOW TO IMPROVE BINOCULAR IMAGE QUALITY?

Several options exist. First, lens treatments: applying coatings like magnesium fluoride reduces light diffraction. On our 100 series, MC (Multi Coated) treatment yields nearly 70% light transmission. Our 500 range features FMC (Full Multi Coated) on all lenses, achieving 78% transmission. The 900 range uses FBMC (Full Broadband Multi Coated) for nearly 83% transmission. With HTR models, transmission reaches 92%.

You might wonder: why not apply premium coatings to entry-level 100 models? Lens coatings are the most expensive part of binoculars—far exceeding chassis or grip costs. Between an MC and FBMC binocular (or our 100 and HTR levels), coating costs differ by 15 times. This directly impacts retail price and performance. To balance affordability and optical performance, we offer models with varied coatings, reflected in our step-up range from 100 to 500, 900, and HTR (comparable to a 1200 level).

Graph of light spectrum transmission curves for aluminium, silver, and dielectric coatings

WHAT ABOUT PRISM TRANSMISSION RATES?

On our 100 series, an aluminium-based coating is applied to the prism. While suitable for twilight viewing, a 100 10x42 model offers high contrast in daylight but reduced contrast at dawn or dusk. On 500 models, transmission improves on warm tones (such as sunset hues), providing high-contrast, bright viewing in low light. The 900 10x42 binoculars (featuring a dielectric coating) deliver homogeneous transmission: nearly 83% across all light wavelengths. This ensures sharp, neutral contrast throughout the day—especially useful during dusk stalking, high seat hunting, or late wildlife observation.

Our 900 binoculars deliver central image detail resolution of 0.8 arcminutes. For comparison, human eye resolution averages around 1 arcminute (equivalent to a football at 800 metres). This elevated resolution sharpens perceived contrast and brightness.

Technical focus on the assembly and sealing gaskets of a Solognac chassis

CHASSIS MATERIALS IN BINOCULARS

Finally, let's cover chassis materials. Our 100 and 500 series feature plastic chassis, whereas 900 and HTR models use magnesium. Magnesium offers high resistance to impact and thermal expansion. Thermal expansion is crucial if binoculars remain in vehicles. On hot summer days, temperatures inside cars rise significantly. Plastic chassis tend to expand under extreme heat. We advise against leaving optics in cars: internal anti-fog gas in plastic chassis models (levels 100 and 500) could escape due to expansion, causing internal fogging. Avoid exposing 100 and 500 binoculars to extreme temperature fluctuations!