What do coatings, seals and gas fillings do?
Optical coatings are extremely thin layers on glass surfaces. Some reduce reflections and the resulting light loss. Others help water bead off or make cleaning easier. A water-repellent layer therefore has a different job from an anti-reflection coating.
Optical coatings are extremely thin layers on glass surfaces. Some reduce reflections and the resulting light loss. Others help water bead off or make cleaning easier. A water-repellent layer therefore has a different job from an anti-reflection coating.
Seals protect the interior from moisture and dirt. A dry gas filling can also help prevent internal fogging. The housing must remain sealed for this to work. Fogging on the outside is still possible: changes in temperature can cause moisture in the air to condense on the outer glass surfaces.
Descriptions such as “weatherproof” or “fog-free” are meaningful only together with their test conditions. These may include a test standard, water depth and duration. Opening the housing can compromise the seals and gas filling. Moisture inside should therefore be assessed by a specialist. Cleaning the exterior cannot repair a damaged seal or replace a lost gas filling.