Daa 1.8 FE has no OSS, therefore cheaper 

No, this is just for the mirrorless canons 

If the gh4 is a micro 4/3rds system then it will work. I have quite a few Nikon and Sigma lenses including the 50mm afs and they all fit and work perfectly. You will have to set your aperture and focus manually but the camera will make all the necessary exposure adjustments itself. Don't forget on a 4/3rds system your 50mm will be 100mm based on a full frame. Make sure your camera is a micro 4/3rds and not a 4/3rds, I have both. 

there are 7 filter ring adapters, included 52mm/ 58mm/ 62mm/67mm/ 72mm/ 77mm/ 82mm, allows you use the nd filter on your kinds of size camera lens. 

Hi 49mm variabel nd you are asking, could you pls tell us your lens type instead of the camera model? Your camera's lens thread size will be marked somewhere on the lens barrel. This number is always preceded by a "Ø" (diameter) symbol. Eg. Ø67mm=67mm thread size. Or please contact us via Amazon, all messages will be replied in 24 hours. Kind regards, K&F Concept