AoP: Exercise 3 - Focus at different apertures

Exercise 3 asked us to shoot the same scene using a range of different aperture settings.

Again I used the collection of 3 film cameras and focused on the press camera in the middle.  I then took 3 exposures with decreasing aperture size.

f/5.6

f/11

f/22

I was shooting in my living room and was keen to avoid the harsh overhead lights, or the camera's onboard flash.  With these considerations I was already shooting on fairly long exposures whilst wide open.  The small aperture required for some of these shots meant long exposures (25 seconds in the last shot).

Conclusion:  

Everything else being equal, depth of field increases as the aperture decreases in size.  With the aperture wide open we can use the shallow depth of field to draw attention to our plane of focus.  With the lens stopped down, more of the picture becomes sharp.  Whilst the limits of acceptable focus are fairly subjective, it cannot be denied that the in focus area is increasing in depth as we progress through the 3 images.

Looking at hard copies of the images I noticed another effect; the in-focus areas of the f/11 image look sharper than the in-focus areas of the f/22 image (although more of the f/22 image is in focus).  There are lots of possible explanations I can think of for this:

1) A comparative effect.  With something softer to compare it to we might perceive the sharp bits of the picture to be particularly sharp.

2) A diffraction effect.  When the lens is stopped down a lot the lens starts to behave like a pinhole and light rays will become diffracted as they pass through the small aperture.  This could produce an overall softening of the f/22 image.

3) Camera wobble.  The f/22 image required a very long exposure time to compensate for the low amount of light that was being transmitted through the small aperture.  Camera wobble over the duration of the shot could have caused the shot to soften.

My shot notes for this exercise can be seen below: