Lens Diffraction

Objective
Determine the fall-off point for resolution/sharpness for my 10-18 mm lens.

Context
Resolution/sharpness is affected by the size of the aperture. At larger apertures (2.8 or 5.6, for example), the light reaching the sensor is well resolved and the image retains sharpness. As the aperture size decreases, some of the light hits the edge of the aperture and does not land ‘straight’ on the sensor, reducing sharpness. The effect is worsened at even smaller apertures, because less light is reaching the sensor at the angle of incidence.

F Stoppers, What Is Lens Diffraction And How Does It Affect DSLR Photography?
Spencer Cox, What Is Lens Diffraction?

Process
I want to determine the range of apertures at which I can retain a high degree of resolution. The camera will be tripod mounted and I’ll be shooting at a fixed focal length using the following f stops: f/5.6; f/8; f/11; and f/16. In PS, I’ll zoom to 100% and compare the sharpness and resolution. 

Expert Photography, How to Easily Understand the Exposure Triangle

Exposure

At constant ISO = 100, the shutter speed was adjusted to +1 stop for every stop down in aperture.

Results

f/5.6, uncropped
f5/6, cropped to 100%
f/8, cropped to 100%
f/11, cropped to 100%
f/16, cropped to 100%
Comparative cropped

Conclusion/Final Thoughts
I chose my composition because it had a lot of edges and straight line detail, which I thought would show the differences well. The drainpipe, chimney stacks, and the roof eaves in particular are subtly yet evidently sharper when shot at the bigger apertures.

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