What if you failed to make any of the sharpness checks just described and are faced with a soft image? Or at least soft where it counts? Yes, there is a software solution, up to a point. Standard USM (Unsharp Mask) Sharpening is not much help, as it doesn’t address the root cause, but instead tries to fix things by heightening the contrast across a few pixels. You might get some apparent improvement by applying some USM to selected areas only, but this kind of sharpening becomes obvious and objectionable when used even slightly aggressively. What’s needed is software than can calculate the exact amount of blur and then attempt to restore it. De-blurring software, in other words. The procedure is called deconvolution, and involves finding the amount and shape of the original blur, then reconstructing the image by reversing the blurring. It is process-intensive and complex, and while de-blurring receives considerable attention in research papers and for security uses, there is very little available commercially.

Just how important is focus to your composition? Many photographer gurus often describe it as the very basic skill to learn in photography. Without focusing skill, you will be able to achieve abstract images only, distorted images which you can't tell what it is or an image that looks like its a whole background. You can read more tutorials and guide here: Digital SLR Photography Guide.

Luckily, Photoshop has a filter that attempts this (Filter > Sharpen > Smart Sharpen, then either Focus Blur or Motion Blur), but dedicated software appears, at least on the test, to perform more effectively. One plug-in that works well in many situation in Focus Magic, which includes a function for estimating the amount of blur (this is measured in pixels). A warning, however-the maximum softness of focus that is correctible is in the region of about 20 pixels.

A focus mistake is often achieved in which the lens aperture was wide, and thus gave a shallow depth of field. Focus can be repaired using Focus Magic, a Photoshop plug-in, on a duplicate layer.

Motion blur can also be tackled by the same software, and the result are often more striking, as doubled and streaked features spring back into recognizable features.

Read more DSLR Photography Guide on the official site: Digital SLR Photography Guide.