jquery - Creating a viewhole or round circle into an element with background image to see through? -

what trying achieve this:

a sidebar slides in, not 1 still image animation. trick is: not 1 color, background image used in sidebar blurred image of sharp background image. if scroll down, scroll position of blurred background image along, gives blurry lense effect.

people afterwards can scroll down , viewhole should adjust. solution can think of duplicate background image in front of slidebar in element circle, , scroll accordingly well. feels overkill. there no better solution?

i reading here not seem there way allow background images.