What is the Depth of Field?

There are plenty of in depth pages on the subject on the internet (Here is a very good one), my goal is not to add one but to briefly summarize.

The Depth of field is simply the zone in your image where objects are going to be in focus enough to look sharp in print . Every camera manual has a little chapter on the matter explaining how to reduce the DoF when shooting a portrait by using the largest aperture available (the smallest possible f: stop) or how to create the largest possible DoF shot by using the smallest aperture (the largest f: stop).

This is all nice and easy but comes the point where you want to get very close to your subject (macro-photography); Unfortunately, two other factors influence the DoF: The focal length (x mm) and the subject-lens distance. Reducing the subject-lens distance reduces the depth of field. See the next image of a metal ruler placed as close as possible to the front lens. The Olympus is set on Manual Focus at 2 inches or 5 cm .The aperture is f:8 to maximize the Depth of Field.

Because we are so close to the lens, the Depth of Field is less than ⅜ of an inch or 1 centimeter, even at f:8

Apparently engineers at Olympus do not measure from the front element of the lens since the camera focuses at 1⅛. of an inch or 2.8cm.
Note that I am in no way complaining about this!

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The photo bellow shows the DoF when shooting a hibiscus with the lens as close as possible to the subject
See how only the top of the stigmas are in focus, the anthers (yellow) are completely blurred because of the narrow DoF.

Here is the same photo after my process.