Focus stacking
Focus stacking combines several photos, each with a different point of focus, into one image that's sharp throughout. It's essential for macro and landscape, where a single shot never gets everything sharp front to back. The software takes the sharp parts from each photo and merges them.
From a tripod, shoot a series in which you shift the focus point a little each time, from front to back. Then merge them in Photoshop (auto-align and blend layers) or in specialized software. Make sure there's enough overlap in sharpness between shots, or you'll get blurry zones between the layers. It's a technique that takes patience, but for macro it delivers a sharpness that no aperture can achieve in a single shot.
Read also the in-depth explanation: Focus stacking explained.
Related terms
Prefer a look in one click?
The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.