Which of the following techniques is likely to create the deepest depth of field?

The technique that is likely to create the deepest depth of field is utilizing a narrow aperture. When a narrow aperture is used, it increases the range in which objects are in focus within a scene. This means that a greater area, from the foreground to the background, will appear sharp and clear.

The physics behind this involves the light rays entering the lens through a smaller opening (narrow aperture), which allows less light to hit the sensor but also reduces the influence of lens aberrations and focus fall-off. As a result, more of the scene is rendered sharply in focus from close to distant objects.

In contrast, a wide aperture would produce a shallow depth of field, making only a small portion of the image in focus, while a low ISO affects the image's sensitivity to light but does not inherently influence depth of field. Lastly, using a short focal length can also increase depth of field, but the effect is not as pronounced as using a narrow aperture, which is specifically designed to maximize the depth of field. Thus, using a narrow aperture is the most effective method for achieving a deeper focus in an image.