How do I blur a part of the screen only? (Not being selective of objects, but a visual part of it)

As you can see in the picture above,
There’s 2 cameras, the Main camera, and the Blur camera.
And the entire screen has been blurred by the Blur camera, over the Main camera.

I only want the area of the blank panel to be blurred, not the entire screen.
The rest of it, I want clear view, as intended (by the main camera, which is exactly the same as the blur camera except for being in a different layer and without the blur).

What I’m looking for, is there a layer mask (like in photoshop) which I can use to alpha out only the portion i want from the blur camera?

Most other questions I look at talk about culling objects from a particular camera, rather than an area of it.
(Please excuse my noobishness. I’m very new to unity, it hasn’t even been a month.)

Hey there,

I dont have a lot of experiance with this sort of thing but my first thought would be, if you know the exact size and pos of the non blur section, try to render the non blur camera ontop of the blur camera in just that space, Perhaps this can help Unity - Manual: Using more than one camera