Dust and moisture are the natural enemies of DSLRs. If they get into you camera they can cause all sorts of problems ranging from dust on the sensor and image degradation, to fungus growing inside a lens. The Dust Donut is a simple idea which has been launched on Kickstarter and aims to solve the problem of non-weather-sealed lenses by adding a seal between your camera and lens.
Designed for Canon EF lenses (the majority of those sold lack any form of weather sealing) the Dust Donut is essentially a rubber gasket which attaches to the mounting surface of the lens and provides a seal between the lens and camera. By blocking dirt and moisture from collecting around this connection, it reduces the risk of damage being caused to your sensor.
Once applied directly to the mounting surface of the lens, the Dust Donut is said to require no further attention. Obviously this is unlikely to offer you the same level of protection as a weather-sealed L-series lens, but some protection is always going to be better than none. A separate Dust Donut will be required for each lens that you want to add a level of weather sealing to.
Dust Donut creator, California-based photographer Tyler Sterbentz, says it "fits as if it were made by Canon" and will be manufactured to a level of precision found only in aerospace engineering. This means no overhangs or gaps which could allow leaks, and the thin rubber disc will not make it any harder to attach or remove a lens from your DSLR.
Having already exceeded its Kickstarter goal with 35 days to go, the Dust Donut is due to start shipping to backers in April. A pledge of US$20 will get you one to fit a Canon EF mount lens, including third party brands. The creators say that Nikon, Olympus and Sony versions are on the way and a Kickstarter pledge of US$3 will get you on the priority mailing list for future versions.
Below is a quick video explaining the Dust Donut.