One way of applying sharpness to a photograph
The Unsharp Mask tool is my favourite tool when I want to control sharpness in one of my photographs. It´s a very efficient tool which will give you great opportunities when applying sharpness - but it´s also a tool which effects can be easily overdone - so I would advice you to apply sharpness with caution. An overly sharp photograph looks kind of vulgar, well downright ugly if you ask me. But done with a "light hand" it can produce stunning and delicate results.
And whatever you do - unsharp mask is the last tool to use in the photo editing process. Once applied sharpness gets spoiled by later, and other, editing. So save unsharp mask till the very end.
On this screendump you´ll see a typical version of the tool. On the thumbnail photo you´ll be able to follow the changes applied to the photo on just a fragment of the picture.
When I use this tool, I usually start by placing the "Amount" slider somewhere at the right end of the line. As in this example.
Then I adjust the "Radius" slider carefully, starting from the left side. Just to the point where I think the picture is sharp enough. It´s often overdone if you spot thin white lines along the original edges in the photo. This takes some experimenting and practise to get this right. But don´t panic - everything can be undone. If you leftclick on the thumbnail, you will see the sharpness as it was before you started adjusting. That way you can easily follow what changes are made.
When the photo is sharp enough, you´ll very often - to your regret - find that noise is suddenly visible in the picture. Noise that has been there all the time, but has become visible because of the sharpening. For that we have the "Threshold" slider. Adjust it slowly starting from the left untill the amount of noise is tolerable.
Then fine-tune all sliders till you are satisfied. Save the result as a copy and open it in a viewer. If you´re happy with the result, then congrats. If you´re not, you can try again starting from the original photo.
Or you could try another solution. When having adjusted Amount and Radius, ignore Threshold but instead create a new layer as a copy. Then apply a lot of Gaussian Blur to the new layer - blend the two layers till the point where you´re satisfied, flatten the picture and save as a copy. That usually works in order to remove noise as a result of sharpening.
Good luck with your efforts.