OLYMPUSOlympus introduced the Four Thirds System (see the "Sensor Formats" sidebar) back in 2003, the first DSLR with a built-in sensor-dust remover (the E-1 in 2003) and the first DSLR with live-view and a tilting LCD monitor (the E-330 in 2006).
Today, Olympus offers the pro-oriented E-5 and mid-level E-30 DSLRs, but has replaced its entry-level DSLRs with its mirrorless Micro Four Thirds offerings, the PEN E-PL1, E-PL2 and E-P2. Inspired by the company's famous PEN compact 35mm cameras of the 1960s, these stylish cameras feature 12.3-megapixel High-Speed Live MOS 4/3 image sensors, effective sensor-dust removers and sensor-shift image stabilization that works with all lenses. All will accept an optional electronic view-finder, and all provide multiple-exposure capability and Olympus Art Filters.
The latest model, the E-PL2, also accepts the new PENPAL PP-1 Bluetooth unit that makes it simple to send images to friends and comes with a new MCC 14-42mm kit lens that provides near-silent autofocusing for movie use.
The E-PL1 and E-PL2 have built-in flash units; all three PEN models will accept accessory flash units. Micro Four Thirds cameras use Micro Four Thirds lenses from any manufacturer, and also can use regular Four Thirds System lenses and many other lenses via adapters.
Like DSLRs, removable memory media have evolved over the years. Today's DSLRs use one or more of three basic types: CompactFlash, SecureDigital (SD) and Memory Sticks. While the cards vary in physical size, all do the job (storing images) quite well, the newer versions being quicker and offering higher capacities. Get the type specified for your camera to avoid speed/capacity incompatibilities.
The top CompactFlash cards are the UDMA (Ultra Direct Memory Access) ones; they're faster than previous versions, but only if your camera is UDMA-enabled. Today's CompactFlash cards come in speeds of up to 100 megabytes per second and capacities up to 64 GB.
The top SD cards are the SDHC (SD high capacity) and SDXC (SD extra-high capacity) ones. SDXC cards are available in capacities up to 64 GB (the format has the potential to go to 2 TB) and speeds up to 35 MB/sec. Again, get what your camera's manufacturer recommends; cameras as well as cards have speed and capacity limits.
Sony's DSLRs use Sony Memory Stick media, which are available in capacities up to 32 GB and speeds up to 30 MB/sec. (for Memory Stick PRO-HG Duo HX).