How can I prevent lens or filter condensation during night and early-morning shooting?

Question

When I shoot at night or early in the morning, moisture condenses on the front of my lens or filter and I end up wiping it every few minutes. Is there a lens-safe way to prevent or slow this condensation?

user3335 · Answer

I'd like to apologize for the rough render with poor detail. This answer does not use any magic, but rather chemistry!

Heated UV Protection Filter

The lens warmer uses two two fins, each with a hand warmer rubber banded to it to heat the glass element. The heat from the warmers will quickly get the filter element above ambient temperature, at which point it will no longer condense.

Quick render of a proposed lens warmer

Usage

Attach HPF (heated protection filter) to camera before entering concerned ambient conditions.
Open one or two hand warmers depending on severity of conditions.
Hold one warmer over the glass to quick heat the element.
Attach warmers to HPF warming fins.
Use camera as normal, taking care not to damange the attached HPF.

Physical Implementation

This would be somewhat difficult to physically implement with the tools commonly available. I would consider using a step up ring and a filter larger than necessary. Then glue the aluminum heating plate to the step up ring, and glue (thermal adhesive please!) the filter on top of the plate. A hole has been previously drilled in the plate to allow light to pass.