From George Douvos:
TrueDoF is a major step forward in working with depth of field:* The TrueDoF family of depth of field calculators uniquely takes into account the effects of diffraction (the blurring caused when light passes through small apertures).In using the app, you will notice that, as you increase the f-number, you reach a point where the depth of field actually begins to drop. This is due to diffraction. At some large f-number, the width of the region of acceptable sharpness drops to zero. This is because, at such an f-number and above, diffraction produces so much blurring that you cannot achieve the sharpness standards you have specified on the settings screen.That the effects of diffraction be taken into account is particularly important for users of digital cameras with sensors smaller than 35 mm format, where diffraction seriously compromises image quality at the top end of the aperture scale. Lenses on 35 mm cameras stop down to about f/22. Theres a reason why they dont go any further. But f/22, or even f/16 or f/11, is too much for cameras with smaller sensors. With TrueDoF, you can avoid using aperture that are damaging to image quality.* Depth of field depends not only on focal length, focus distance and aperture, but also on the desired output quality. With TrueDoF, you work directly with the desired output: How big a print do you want? How sharp an image is sufficiently sharp for you? Stick with the default values, set them to your own personally acceptable default values, or vary these quantities as the need arises. Whatever you choose, its all intuitive, simple and fast.A note on intended use:TrueDoF is designed for photographers who want an accurate, versatile and easy way to calculate the depth of field produced by their chosen camera settings.There are some types of photography, e.g, landscape photography, where it is preferable to work the other way around, i.e. first specifying the depth of field you want (by setting the distances to the nearest and furthest objects that you wish to appear sharp in your photograph) and, from that, determining the camera settings (focus distance and aperture) that will give you the sharpest possible image. For that approach, check out OptimumCS-Pro, the unique optimum camera settings calculator, also available on the App Store.And, if you would like to achieve insanely huge depth of field - with astonishing image sharpness - try the FocusStacker app. Now it's remarkably easy to achieve consistently excellent results when using the focus stacking technique in landscape and architectural photography.