Are these scopes Fog Proof Externally? I bought a new. Vortex scope and first use in the field it fogged up once I placed close to my sweaty eye. — 1 Answer

We are not entirely sure what is meant by “external fog proof”, but the lens surfaces are treated with a multi-coating. When you breathe on these lenses, they fog up briefly. We believe the same thing happens when moisture evaporating from around a warm, sweaty eye causes the lens to fog. For March Scopes, in recent years, an additional hydrophobic coating has been applied on top of the multi-coating for the lens surfaces exposed to the outside environment. The hydrophobic coating prevents rainwater from spreading across the lens surface. Instead, water forms small droplets that roll off, helping to maintain visibility. When you breathe on this type of lens, it does not fog as heavily as a lens with only a multi-coating — the fogging remains light. For this reason, we believe lenses with a hydrophobic coating can be considered to have an “external anti-fog specification.”
In addition, the hydrophobic coating feels noticeably smoother than standard multi-coating, making it more resistant to dust adhering to the surface. As a result, it is also expected to reduce the adhesion of powder residue. It seems that the hydrophobic coating material used for eyeglasses — a type of fluorinated compound — is the same type that is vapor-deposited on riflescope lenses as well. Answered by DEON Optical Design (manufacturer of March Scopes)