Convert a lens to its full-frame (35mm) equivalent focal length, and the equivalent aperture for depth-of-field comparisons, for any sensor.
Crop factor compares a sensor to full frame (35mm). The equivalent focal length is the full-frame lens that frames the same view. The equivalent aperture scales the f-number by the same factor for depth-of-field and light-gathering comparisons.
It is the ratio of a sensor diagonal to a full-frame (35mm) sensor. APS-C is about 1.5x (1.6x for Canon), Micro 4/3 is 2.0x. Multiply a lens focal length by the crop factor to get the full-frame equivalent angle of view.
Multiplying the f-number by the crop factor gives the full-frame aperture that produces the same depth of field and gathers the same total light. So an f/1.8 lens on Micro 4/3 behaves like f/3.6 on full frame for depth of field, even though it exposes at f/1.8.
No. The f-number for exposure stays the same on any sensor. Crop factor only changes the framing (equivalent focal length) and the depth-of-field comparison (equivalent aperture).