I've known for some time that there are adapters to allow Nikon / Canon fit lens to work on the Micro Four Thirds (MTF) system.
I was able to borrow a MTF to Nikon adapter along with a Sigma 150-500mm lens from a friend (thanks Mr P) so I was able to test out to see just how well it worked.
Cameras used for this test were Olympus OM-D E-M1 with the Sigma and the E-M5 with the Olympus 75-300mm lens.
With its x2 crop factor the 500mm worked out to 1000mm full frame equivalent.
My first problem was not being able to change the aperture of the Sigma. The bigger problem being that the aperture seemed to be stuck toward at its maximum aperture of f/28. With no way of changing this it meant for a far too slow shutter speed, and a the need to use a fairly high 1600 ISO.
With none of the auto functions of the lens working, it was manual focus only. Not a huge problem for the static subjects I was shooting while testing.
Due to the problems with the aperture the comparison shots here aren't really fair, with one of the images at 200iso and the other at 1600iso. I'll include them so you can at least see what the difference in reach is.
The only way of perhaps changing the aperture of the lens would be to put it on a Nikon body. I know that sometimes you can fix the aperture on the lens by selecting it via the camera body, and then removing the lens without turning the camera off. Would that have worked in this case? I simply do not know. Something for someone else to test.
In conclusion, would I buy myself a big lens to use on a small camera, probably not unless it was designed to work fully with said small camera.