Heavy fog mainly means prolonged moisture exposure. If your camera and lens are weather-sealed/weather-resistant, they can usually handle fog better, but they are not fully waterproof. If they are not weather-resistant, use a rain cover or other camera rain protection.

Key precautions:

• Avoid changing lenses in the fog, since moisture can get inside the camera.
• Wipe off external moisture as needed and keep unused gear covered.
• After the shoot, dry the gear out in a sealed bag or airtight container with silica gel/desiccant packs to help remove residual moisture.
• In very wet conditions, consider using a waterproof compact camera and keeping your main kit protected unless needed.

In general, brief fog exposure is often manageable, but persistent condensation and water droplets are the real concern. Protect non-sealed gear, minimize opening the camera system, and dry everything thoroughly afterward.