To sharpen, or not to sharpen, that is the question? not exactly Shakespeare I'll admit but it's a question I often get asked.
So whats the answer? Well pretty much all digital images need some sharpening. You see the way digital cameras work actually softens the image slightly, theres a filter over the sensor in most cameras called the Anti Alias filter, this is a bit of clear glass but slightly blured like a bathroom window, it's job is to smooth out the light on the sensor and to help remove moire patterns (that sort of checker pattern you sometimes see on clothing with a fine texture or pattern) Trouble is it removes a little of the sharpness in the camera, this is where capture sharpening comes in to replace this effect.
Now there's lots of differing opinions about sharpening, but the top people generally agree a 3 step sharpening route is the best way to go.
Step 1 Capture sharpening, this is a mild sharpen just to replace the sharpening lost to the AA filter.
Step 2 Creative sharpening, this is where you sharpen only parts of an image for effect, maybe just the eye's and hair in a portrait, or the in focus foreground in a landscape, usually done with layer masks to limit the effect.
Step 3 Output sharpening, this is where you sharpen the whole image to the final size and output type, printing needed more sharpening for matt papers and larger sizes etc.
Now not everybody uses all 3 steps, but the first 2 are the most important (some printers add sharpening by default anyway)
Then there's different ways of sharpening, one of the more popular with the more advanced photographers is the "Hi-pass" sharpening, often mentioned in hushed tones by tog's huddled in corners, the way it works is pretty much edge sharpening (over simplified) The way to do it is to create a duplicate layer, then filter/other/ high pass, set about 10 as a starting point then change the layer blend mode to hard light, now ajust the opacity of the layer till your happy.
In the image above I have just used hi-pass with no other sharpening on the left half, the right sides had no sharpening at all.
Wayne