Hi,the filter kit (SKU.1877) has adapter rings(67mm/72mm/77mm/82mm) and separate 49mm/52mm/55mm/58mm/62mm adapter rings to sell,it can fit if your lens size is included. 

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 

Since the Olympus e520 is a Four Thirds sensor this adapter will NOT work with it. It is made for Micro 4/3 sensors, not 4/3. 

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