Note the G1 X II lens is 24-120mm 35mm film (FF) equivalent[/b] . With the 1.92 crop factor, the lenses aperture is FF equivalent to f/3.8-7.5, not exactly fast! You can use a f/1.2 or 1.4 primes on the EOS-M and for FF equivalent apertures of f/2 to f/2.2, something the G1XII can't get close to.
The f-ratio of the lens didn't change... the field of view is equivalent to 24-120mm 35mm FF.
Have a nice day.
I didn't say the f-ratio changed, that is the ratio of the focal length divided by the diameter of the entrance pupil of the lens. However, the equivalent f/stop is different when comparing cameras with different sensor sizes.
The attached article explains it much better than I can. Note the "Depth of Field Equivalents" calculator and explanation half way down the page.
Canon apparently created a new sensor size for the G1XII (according to this description from their website: "Focal Length - 12.5mm (W) - 62.5mm (T) (35mm film equivalent: 24-120mm)". So, this would be a 1.92x crop factor, which is very close to the micro 4/3 sensor on the chart (2x crop factor).
This is a quote from the Cambridgeincolour article:
As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance). This is because larger sensors require one to get closer to their subject, or to use a longer focal length in order to fill the frame with that subject. This means that one has to use progressively smaller aperture sizes in order to maintain the same depth of field on larger sensors. The following calculator predicts the required aperture and focal length in order to achieve the same depth of field (while maintaining perspective).
Have a good day!