This article is written for the virtuoso large format photographic artist.
If you are a beginner or just shooting a 35mm or digital camera then this article addresses issues which won't bother you at reasonable apertures. Just use a tripod and choose the smallest aperture you have if you need depth of field. Avoid apertures smaller than f/8 or f/11 on digital cameras.
This article is for people shooting film cameras that stop down to f/32 or smaller. At this point the effects of diffraction can start to blur the image more than the effects of defocus due to limited depth of field. In this case one has a paradox, since no longer will using the smallest aperture give the best results. Determining which is the best aperture taking into account both depth of field (which gets better at small apertures) and diffraction (that gets worse at small apertures) becomes a little more involved, and has never been considered in the depth of field charts that everyone has been using for decades.
