All three photographs were taken with a Nikkor 50mm 1:1.8 AF-D lens on my Nikon D50. Focal length equivalent of around 75mm on a full frame camera. ISO was set to 200. Shutter speed varied according to the aperture.
f1.8: A very narrow depth of field; almost everything except for a narrow band down the centre of the image is out of focus; moving out from the focussed strip the quickly becomes very blurred indeed.
f6.3: A wider area of brick is in focus, stretching with a greater increase to the right of the image, where the wall was further away from the camera. The entire image is now readable as brick.
f22: The strip widens again, and – unless you look closely – most of the picture seems clear, if not completely sharp. This time the increase seemed evenly spread on either side of the original in-focus area, which suggests maybe I knocked the point of focus off to the right when I was changing the aperture.
Nothing to add to this really; the smaller the aperture the greater the depth of field. It’s always interesting to do exercises like this and see in practice what the theory says…