On its announcement in July 2006, the E400 entered the world of digital photography as the 
Worlds smallest and lightest DSLR; Nikon has introduced the also svelte D40 since then but it is light four million pixels compared to the E400.
Other key kit includes a highly energy efficient image processor that also helps to reduce problems with noise and provides 3 fps continuous shooting and five frame buffer in RAW shooting. JPEG compression includes (among the more usual settings) a great “SHQ” (Super High Quality) mode that uses less aggressive compression leaving JPEG images without any of the artifacts that become an issue at higher compression ratios.
An anti-dust system uses a Super Sonic Wave Filter that activates whenever the camera is switched on; the filter shakes itself down each time the camera is activated and is placed in front of the Kodak made 10-million pixel FourThirds sensor. While the jury is still out a definitive answer to which anti-dust system actually works well across the various manufacturers that now employ it within their cameras, it is generally agreed the Olympus set up works very well. Olympus E400 DSLR digital camera Review - Pocket-lint.co.uk