Olympus M.Zuiko Digital Teleconverter MC-20

It means your lens's focal length is effectively doubled. For example, if you attach it to a 300mm lens, you will achieve the reach of a 600mm lens, allowing you to get much closer to distant subjects like wildlife or athletes.

Yes, using the MC-20 results in a 2.0-stop loss of light. You will need to compensate by using a higher ISO, a slower shutter speed, or a wider aperture to maintain the same exposure you had without the converter.

No, it is only compatible with specific Olympus M.Zuiko lenses designed to work with teleconverters. You should check the official compatibility list for your specific lens model before purchasing to ensure it will mount and function correctly.

The MC-20 is designed to maintain communication between the lens and camera, but it does not add or enhance autofocus or image stabilization features. Your ability to use these features depends entirely on the capabilities of the lens and camera body you are pairing it with.

Using the MC-20 is generally superior to cropping because it utilizes the full resolution of your sensor to capture the subject. While there is a slight loss of light, the optical design is engineered to maintain sharpness and clarity, which is usually better than digitally zooming in on a smaller portion of an image.