10x42 With Fully Multi-Coated Lenses, Nitrogen Purged
The Crossfire HD pairs 10x magnification with 42mm objective lenses, and every air-to-glass surface is fully multi-coated, with several anti-reflective layers. Each uncoated glass surface bounces some light away, so coating all of them is what keeps the image bright and contrasty rather than washed out. Vortex also says the glass is chosen to cut chromatic aberration, the coloured fringes you can see around high contrast edges. The image is crisp and clean, though a little yellow or purple fringing can still show, which is normal at this level. The exit pupil is 4.2mm, which is simply the objective size divided by the magnification, and the relative brightness of 17.64 is that figure squared. Both describe how much light reaches your eye, which is what matters at dawn and dusk. Inside, the body is nitrogen purged and sealed with o-rings, so there is no moist air to fog the prisms when you move between warm and cold.
