Micro four thirds - does the crop factor apply to MFT lenses as well?

Great Bustard wrote:

Neither the focal length nor the aperture of the lens change just because it's mounted in front of a different size sensor. However, the effect of both the focal length and aperture change in the same proportion as the ratio of the sensor diagonals.

The f-ratio (relative aperture) is the quotient of the focal length and the entrance pupil (virtual aperture) diameter. For example, a 50mm lens that has an aperture diameter of 25mm will have a relative aperture of 50mm / 25mm = 2. We write it as "f/2", where "f" stands for focal length: 50mm / 2 = 25mm.

Here's a little more in depth info on the point:

http://forums.dpreview.com/forums/post/40416852

It's f/2.8, but the effect, in terms of the visual properties of the final photo, is the same as f/5.6 on FF (for a given shutter speed and sensor efficiency).

Lenses are marked for what they are. A 50mm f/2 lens is a 50mm f/2 lens. It is not a 100mm f/2 lens, nor is it a 100mm f/4 lens. However, a 50mm f/2 lens on mFT is equivalent to a 100mm f/4 lens on FF:

http://josephjamesphotography.com/equivalence/#introduction

50mm f/2 on 4/3 (mFT) is equivalent to 62.5mm f/2.5 on 1.6x (Canon APS-C), 67mm f/2.7 on 1.5x (DX), and 100mm f/4 on FF, where "equivalent to" means:

• The photos have the same AOV (diagonal angle of view) and aperture (entrance pupil) diameter: 50mm / 2 = 62.5mm / 2.5 = 67mm / 2.7 = 100mm / 4 = 25mm.

• The photos have the same DOF (as well as diffraction softening) when they have same perspective (subject-camera distance), AOV, aperture diameter, and display size.

• The photos have the same motion blur and the same total amount of light falls on the sensor when the aperture diameter and shutter speed are the same (usually attained by upping the ISO as required).

• The photos have the same same noise when the same total amount of light falls on the sensor if the sensors are equally efficient (less noise if the sensor is more efficient, more noise if the sensor is less efficient).

• Other elements of IQ, such as resolution, bokeh, flare resistance, etc., as well as elements of operation, such as AF speed/accuracy, size, weight, etc., are not covered in this use of the term "equivalent".

Hope this clears the whole matter up for you!