Focus at different apertures Exercise 3

Monday 11th April 2011
Focus at different apertures

Using the same 50mm prime lens with the camera mounted on a tripod and the shutter release cable, I took 3 photo's - f1.8, f11, f22 and compared them after printing.

50mm prime lens f1.8

The red elipse demonstrates the limit of sharpness. I was interested to see it was an elipse shape, as I had assumed the aperture would be a circle. I expected this to be a small depth of field as for obscuring backgrounds and portrait photography I have been taught to use the smallest depth of field possible with the lens used. We have had this lens in the kit bag for some time and I have not worked with it much, so I was keen to experiment as it a good lens for still life photography and low light indoor work.

50mm prime lens f22

The red elipse demonstrates the limit of sharpness.

The middle of this picture is sharp. I expected the whole picture to be in focus. This could be because of bokeh (blurring) and the lens only having 5 blades so it creates a pentagon shape. I have researched this lens on the internet http://www.the-digital-picture.com/Reviews/Canon-EF-50mm-f-1.8-II-Lens-Review.aspx

There is a marked difference between the f1.8 and f22 or f11 because a large aperture gives a small depth of field.

50mm prime lens f11

The red elipse demonstrates the limits of sharpness. I think this is the best photo when printed out as there is more in focus than with the f22. For example, the collars are easy to read.