The Olympus E-330 is a DSLR launched on 30 January 2006, using the Four Thirds System lens mount standard. Its main feature is its live image preview functionality, permitting an image to be previewed on the LCD screen. While live image preview is not new in compact digital cameras, the E-330 is significant because it was the first digital SLR to offer this feature. With the ability to digitally zoom in 10× before taking a picture, it is very well suited for exact manual focussing, for example in macro photography.

The Four Thirds System is a standard created by Olympus and Eastman Kodak for digital single-lens reflex camera (DSLR) design and development. Four Thirds refers to both the size of the image sensor (4/3") as well as the aspect ratio (4:3). The Olympus E-1 was the first Four Thirds DSLR, announced and released in 2003. In 2008, Olympus and Panasonic began publicizing the Micro Four Thirds system, a mirrorless camera system which used the same sensor size; by eliminating the reflex mirror, the Micro Four Thirds cameras were significantly smaller than the Four Thirds cameras. The first Micro Four Thirds cameras were released in 2009 and the final Four Thirds cameras were released in 2010; by that time, approximately 15 Four Thirds camera models had been released by Olympus and Panasonic in total. The Four Thirds system was quietly discontinued in 2017, six years after the final cameras were released.