Exercise 3: Focus at different apertures

This turned out to be a strange exercise and definitely did not yield the results that I had expected. The brief here was to take the same picture with the same focus point at different apertures (widest, middle and smallest aperture) I used a 50mm prime and took 4 photographs at f1.8; f5.6; f11 and f22. We were asked to ensure that the shutter speed adjust accordingly so as to ensure an even exposure value across the photographs. I decided to shoot in Aperture priority and set the ISO to automatic. Shutter values were, respectively 1/4000; 1/400; 1/100 and 1/500. ISO remained constant at 100 except for the f22 shot where the camera increased ISO to 200.

Despite the even exposure I was expecting to see some drop in brightness, but the camera performed very well, certainly at a causal glance there is very little difference in brightness to the images. I was expecting softness away from the focus point, what I wasn't expecting was the lack of sharpness at the focus point when the lens was wide open and also when the lens was at it's smallest aperture. I had always assumed that at it's widest aperture, while most of the image would be soft, the focus point would be sharp and detailed. Not so. I deliberately chose to shoot trees on southbank from across the river. The f1.8 and f22 photos are surprising soft and lack detail even at the focus point, while the f5.6 and f11 photos are crisp and clear across the whole photograph, not just at the focus point. what is  nice about the f1.8 shot is that the branches in the foreground are nicely out of focus and it mimics the way the eye will hone in on on the specific point of  view. It detracts less from what is being observed. What was also surprising was the level of chromatic aboration which disappeared as soon as the lens was stepped down to f5.6

It's hard to tell from the resized images, but at full size at 100% you can read the names of the boats and the signs on the buildings in the f5.6 and f11 photos, whereas at the extremes in the aperture range the signage is difficult to distinguish clearly.  Photographs below with focus point marked as a red dot: