Micro four thirds is a camera standard or design created via a partnership between Olympus and Panasonic. The design does away with the mirror and prism system found on traditional DSLRs so the result are very compact cameras.
Camera mounts can be used to marry traditional or legacy lens to M4/3 cameras or of course the growing line of lens created for the M4/3 design are available from Olympus, Panasonic (with lens designed by Leica).
One of the big advantages of the M4/3 camera is the compactness of the lens. Because the len sits closer to the sensor, the effective focal distance doubles. So a 20mm M4/3 lens is the equivalent to a 40mm traditional lens.
Quite a number of the available M4/3 lens turn out to be a huge cost savings when you compare them to lens in traditional formats. For example the Panasonic 100-300mm is around $600. Compare that to the cost of a 200-600 mm lens from Cannon or Nikon.
Over the past year I've been taking images with a Panasonic DMC-G2 with a 12 mp sensor and recently upgraded to the DMC-G3 with a 16 mp sensor.
I ditched the kit lens as it wasn't sharp enough for consistent acceptance and currently have three M4/3 lens:
Panasonic 20mm f1.7 - Tiny "pancake" lens that's great for walking around town. Only issue is occasional lens flare issues in studio lights. Fantastic low light capabilities and boken or background blurring.
Blueberries - P 20mm 1-7mm
Panasonic 14-45mm f3.5-5.6 - This is the superior replacement to the current kit lens. Nothing overly exciting or exotic about this lens but its a good overall lens.
Dog Running - P 14-45mm
Panasonic 45-200mm f4.0-5.6 - very good on tripod. I've moved towards this as my favorite in the studio. I can get very sharp images out of this lens. Hand holding can be trickier unless you have enough light to use fast shutter speeds. A real bargain for around $250.
Using the LCD screen for touch focusing on the spot you want to focus is key to the great result. Relying on the camera to pick a focal point just ain't going to cut it.
Barnyard Chickens - P 45-200mm
So my point in writing this was to see what other's in the "M4/3 club" might think about M4/3 lens. Comment below and let me know what you think about your M4/3 lens...