Weather sealed lenses
There’s a distinct difference between weather-sealed or moisture-resistant designed lens and a waterproof lenses. A waterproof lens is designed to withstand a large amount of water coming from different directions at high pressure and prevent it from entering the lens. Some waterproof lenses by their design can be immersed in water up to a certain depth for a specified period of time. Weather-sealed lenses, on the other hand, are designed to withstand small amounts of water or dust without pressure, and cannot be immersed in water. They have O-ring seals that keep unwanted water and dust out. Think of weather-sealing on a lens like having an umbrella or a rain jacket and hat in the rain. If you are uncomfortable with the amount of rain or dust you are encountering, then you might want to get the lens back indoors. All Tamron lenses have moisture-resistant (weather-sealed design).
Rules of thumb when using a moisture-resistant lens:
1) If you are uncomfortable out in the elements it’s time to bring the lens back indoors.
2) If your lens gets wet, dry it off, and if it gets dusty use a lens brush and dust it off.
3) If your lens gets wet with salt water use a cloth with fresh water to clean it off. The worst thing you can do to your camera gear is to expose it to salt water.
4) Make sure that your camera body is also weather sealed.