Let’s acknowledge the elephant in the room right away: Sensors don’t automatically give you the optimum sharpness from your lens, regardless of the lens quality. All digital images need sharpening to get the most from the lens.
The individual photosites or "pixels" on your sensor aren’t completely isolated. To put it simply, they spill information between and among them, which reduces the sharpness from your lens.
If you shoot JPEG, you can have your camera add sharpening to the image while it’s being processed in the camera. Almost all cameras add some sharpening to a JPEG file by default, though you can turn this off or adjust it to a different level in most camera menus.
RAW files have no sharpening applied to the image file at all. You need to apply some sharpening to the image either after you’ve processed the photo in your image- processing software or during RAW conversion. Here are four possibilities.
Unsharp Mask or USM (in the Filter Menu in Photoshop or the Enhance Menu in Photoshop Elements) has been a standard part of sharpening since Photoshop started. It needs to be applied to a flattened image as a last step, after all other processing is done. The reason? There are some adjustments that you make in these programs that can cause problems if the image has already been sharpened. Plus, an image should be sharpened at its final size.
USM has three parts: Amount (the intensity of the sharpening); Radius (the distance sharpening occurs around a pixel); and Threshold (when sharpening starts to occur when two points are different in brightness). There are many formulas for these, and frankly, they mostly all work because different subjects need different amounts of sharpening. I find these numbers work well for me: Amount—100-180 (depending on the subject); Radius—1-1.5 (larger images typically need the higher amount, but watch for unwanted rings or halos around contrasty objects); and Threshold—3-6 mostly, with a maximum of 10-12 (mainly used to avoid sharpening noise).
Smart Sharpen (in the Filter Menu in Photoshop) and Adjust Sharpness (in the Enhance Menu in Photoshop Elements) are the same sharpening function, just with different names—a fairly recent addition to Photoshop products. You still need to sharpen a flattened image last in your workflow. This is a very good way to sharpen your photos, and its algorithms work well. You have two main controls: Amount (intensity) and Radius (distance).