I bought a Olympus 55mm f1.2 from the 70s for a few bucks on a flee market. It has a OM-bajonett. OM used full frame film (24x36mm). Then I bought an OM to M4/3 adapter. I put the lens on my motion picture camera, which has a sensor of 17x13mm, which is a crop factor of 2; standard for m4/3. So I expected an effective focal length of 110mm (in relation to a full frame size).

But after I compared the field of view with a Panasonic 14-140mm M4/3 lens, it showed that it is more or less the same like 55mm on that M4/3 lens. A little bit more, 58 or 60 ca.

I always assumed, that if Panasonic sells a lens for the m4/3 standard, the value for the focal length is converted to the 2x crop factor. So, in their product description panasonic says e.g. it is a 25mm lens, and they add that that is equal 50mm on full frame. Which means, that if you want to have the same angle on a 2x larger sensor, you have to use the double focal length.

Sooo, if this is correct, why the hell gives my old Olympus 55mm lens the same angle on my m4/3 sensor, like my Panasonic 55mm (zoom) lens?