Large scopes issue

I have implemented a 4x scope like in the first image. But the tunnel looks really awful here. In other games like pubg it is removed and some vignette effect is added. Can anyone tell basically how to remove this tunnel look while scoping? You can see in the second image what I actually want to achieve. Thanks.![alt text][1]

You can’t just zoom in on the mesh I’m afraid, you probably need to do it on the HUD.

There are plenty of scope tutorials on youtube: