What is the focal length of the Fujian 35mm on a micro four thirds camera?

Doesn't matter what mount and what format the adapted lens was for. On m43, just double the focal length. In this case it is 70mm.

 

So a 50mm lens (full frame) and a 50mm (APS-C) and a 50mm m4/3 all project the same image onto the sensor.

A 50mm full frame lens just projects a larger image around the sensor that a 4/3 would ignore.

So unless it is a "35mm full frame equivalent C-mount lens", the field of view will be 35mm (m4/3) and 70mm equivalent full frame on a m4/3 camera.

 

35mm

 

Doesn't matter. A 35mm lens is a 35mm lens. The sensor size of m43 is what makes that 35mm transform into the equivalent of a 70mm.

An Olympus or Panasonic 25mm lens is the equivalent of a 50mm lens, yet those lenses are still a 25mm lens. If it was possible to adapt m43 lenses on a FF camera, they would be 25mm and on an APS-C, they would be a 43mm lens.

Simply, don't worry about anything else and just double the focal length of the lens itself.

 

Yes. Lenses are always specified as their actual focal length.

 

It's NOT the focal length that changes, it's the CROP.

ie - A 35mm lens acts like a 35mm lens, but on M43 you get 1/4 the image than if you used the same lens on a 35mm sensor equipped camera. In other words - 2 x crop (The image is 1/4 the size, but the dimension in terms of width, height or diagonal is 2 x on a 35mm vs M43 - well, within reason, as they are different aspect ratios, but lets keep it simple).
Z...

 

Well, the usable image may be closer to a 3X crop factor, which would be a field of view equal to 105mm full frame / 52.5mm m4/3.

But exactly how you crop will be up to you, and the effects/vignetting you want to achieve.

 

Yeah, that's sort of how I read the question (on the basis of vignetting / real usable area), but it sounds like it was just about the mechanics of sensor cropping.

 

+1
or more properly, the field of view.

A 35mm lens on m4/3 has approximately the field of view of a 70mm lens on 35mm full frame. It is not the "equivalent" of a 70mm lens in any other way. Saying so without specifying that you are referring only to FOV is simply wrong by virtue of the omission. It is this omission on so many discussions that causes all the confusion.