Every air to glass surface on an optic is a point of failure. Without specialized coatings, light reflects off the lens rather than passing through it, resulting in a dim, washed out image. High end optics utilize ultra-thin layers of chemical compounds applied in vacuum chambers to manipulate light waves, forcing them through the glass to your eye. Coatings are also applied to protect and increase the longevity of your optic by repelling water and debris while preventing scratching. If you aren’t looking for Fully Multi Coated specifications, you are ignoring the most crucial component of quality optics.
The industry uses four primary tiers: Coated, Fully Coated, Multi Coated, and Fully Multi Coated. Coated is obsolete, a single layer on a single lens. Fully Coated is basic, all air to glass surfaces has a single layer of coating. Multi Coated is a marketing half-truth, guaranteeing multiple layers on at least one surface while leaving others untreated. For the serious hunter, Fully Multi Coated (FMC) is the only relevant specification. It ensures every air to glass surface in the optical stack (often more than 20 surfaces) is treated with multiple chemical layers. This is the baseline for maximizing light transmission, contrast, accurate colors, and eliminating the internal reflections that mask your target in low light.
Phase Correction coatings are one of the most overlooked technical requirements in roof prism optics. As light passes through the prism system, it is split into two out of phase beams. Without phase correction coating, these beams interfere with each other, causing a significant loss in resolution and contrast. This isn’t just a clearer image; it’s the restoration of edge-to-edge sharpness and color fidelity. If your spec sheet doesn’t explicitly list Phase Coated or P-Coating, you are looking at a degraded image that will fail you when you’re trying to pick a bedded buck out of heavy timber. While Fully Multi Coated lenses are a universal requirement for all glass (from your riflescope to your spotter), Phase Correction is the specific gatekeeper for binocular performance.
While Phase Coating handles the alignment of light, Dielectric Coating handles the volume. Dielectric Coating is applied to prisms, not lenses. In a roof prism optic, one surface does not naturally reflect 100% of the light. Without a high-performance coating, you lose significant brightness. Lower tier optics use aluminum coatings and mid-tier use silver, which reflects 95-98% of light. A Dielectric Coating acts as a multi-layer mirror, pushing reflectivity to over 99%. Keep in mind when checking for dielectric coating if the prisms are Abbe-Koenig they do not need to be coated. In the final minutes of legal light, that 4% difference is what allows you to see into the shadows while others are packing up.
The final layer of defense is about protecting your investment and ensuring operational readiness on your hunt. External coatings like scratch resistance, hydrophobic (water repellent), and oleophobic (oil repellent) treatments are non-negotiable for field use. A hydrophobic coating ensures that rain and mist bead off instantly rather than blurring your view at the moment of truth. Oleophobic layers prevent skin oils from smudging the glass, making maintenance effortless. While those don't change the physics of light transmission, they ensure that your glass remains functional when the environment turns hostile. If your lenses are scratched or smeared, the best internal glass in the world is useless.
The bottom-line is don't just look at magnification and objective lens size. Check the coating spec. If it doesn't say Fully Multi Coated at a minimum, keep shopping.