In this exercise I saw the impact of varying the aperture whilst leaving the camera in the same position, framing the same shot and using the same point of focus. I actually took 19 photos stepping through apertures from f1.8 through to f22.0 taking avantage of the range available on a 50mm prime lens. The three shots below are at the extremes plus one in the middle (f9). The camera was set to ‘aperture priority’ meaning whilst I took manual control of aperture, the camera was adjusting the shutter speed to ensure the best exposure for each shot.
Whilst aperture is not the only way depth of field can be altered, this is a good learning exercise of what it can offer in terms of control.
This is the photo with an aperture of f1.8, the point of focus is the first post, the depth of focus looks to be about 2-3 squares of fence to the left of the post and no more than 3-4 squares to the right. The next fence post is very much outside that depth.
This is the photo at aperture f9, the same point of focus (the first post) but this time all the fence to the left of the post seems to be in focus and the right, the second post is now also in focus, the depth of field (to my eye) extend around 3/4 of the way along the fence to the third post before trailing off.
The final photo, with an aperture of f22, this time the posts seem to be in focus as far as the eye can see.