At midday on a bright sunny day with crisp shadows, which aperture is advised and how should it interact with ISO speed?

Choosing an aperture of f/16 during midday on a bright sunny day is advised because this setting helps achieve a deep depth of field while allowing for proper exposure in such bright conditions. At f/16, the shutter speed can remain faster, which is beneficial for capturing sharp images devoid of motion blur, especially in well-lit environments.

Using f/16 also contributes to capturing the distinct details in a scene, as more of the image will be in focus from the foreground to the background. Since the light is abundant at midday, it is essential to select a higher f-stop to control the amount of light entering the lens. In terms of ISO speed, when the aperture is set to f/16, a lower ISO (like 100 or 200) can be used without resulting in overexposure, allowing for great image quality with minimal noise.

While f/22 could provide an even greater depth of field, it can also introduce diffraction, which can soften the image. This makes f/16 a more favorable option as it balances depth of field and image sharpness effectively.