Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It only takes a minute to sign up.
Sign up to join this community
When you adapt a lens for a larger system (full-frame or APS-C) onto a micro four thirds camera, you are essentially cropping the image. Many lenses do not have a problem with this since the focal length is essentially the same from the center to the corners, but fish-eye has a different effect that is critical to the corners.
Do you lose the some/all of the fish-eye effect if you use an adapter, or does an equivalent of the effect carry over to the MFT sensor?
You will crop away the outer edge of the image and this will cause you to lose the highly distorted edges of the photo.
this is particularly obvious when you are dealing with a very very wide angle where normally a circular image would be seen but due to the crop you see a square image.
This review of the Canon 8-15mm fisheye contains a picture how the image will look like on a crop sensor: 
