Yes, no other accessories needed. The filter can be directly screwed on your camera lens. 

EOS-FX,You can use Canon EOS EF / EFS Lens on a Fujifilm FX Mount Camera body,, Your canon ef 75-300 1:4-5.6 is canon EF mount lens and fuji x-a3 is X mount camera body. so the adapter ring fit for your camera and lens. but pls notice, your lens is telephoto lens,we do suggest you could use one telephoto lens bracket that could be attached to the tripod to increase its stability. because the canon lens could not adjust aperture,so suing our adapter ring could not adjust aperture 

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 

Don’t forget that it’s a manual lens adapter. Works with full manual lenses. If your lens has no physical aperture ring, you cannot control it from your camera 

This filter will fit any lens with a 49mm filter thread