By changing the focus you can change the point of focus of the image. With this project changing the aperture changed the quantity of the image that remained in focus. With the aperture f1.8 the dof is incredibly short throwing both fore- and background out of focus. The dof is so short that the mushroom itself is not all in focus. As the aperture is reduced in size from f1.8 to f5 more of the image comes in to focus. And by f22 virtually the whole picture is in focus which also adds clutter and for me detracts from the main focus.
The above image demonstrates how an image can be predominantly out of focus yet can present an object more clearly because of it. Also with the large aperture size, the shutter speed can be faster which helps keep the image clarity high. However, it is worth noting that whilst I focussed on the toadstool, it is only partially in focus and perhaps would benefit from a slightly larger depth of field. I personally favour a short depth of field in imagery - I like simpler and less cluttered images and how your eye is immediately drawn to what you intended.
The aperture is slightly smaller in the above image and I think the image does benefit from it. The toadstool is still the main point of focus and it is now entirely in focus and its' direct surroundings are a little clearer. Yet the detail in the rest of the image is left out of focus.