High-resolution images almost always require some level of sharpening. It's the price we pay for having to image through a turbulent atmosphere. There are many ways to improve the resolution of your mosaic. The nuances of the many image sharpening and deconvolution techniques are way beyond the scope of this article. However, if you have Photoshop you need not look any further than the Unsharp Mask (Filters | Sharpen | Unsharp Mask). The best way to learn sharpening techniques is to experiment. Try using several iterations of the Unsharp Mask (see Figure 8). First use a large radius to sharpen large features and then use progressively smaller radii to sharpen smaller features. Each time you apply the Unsharp Mask duplicate the top layer (Layer | Duplicate Layer...) and use the layer properties of the previous layer to document the parameters used for that layer (Layer | Layer Properties...). For example, "Unsharp 135%/0.9/0." That way if you ever decide you went too far or not far enough, you know what you did earlier, and you have the option of returning to the original image data and starting over.

Use moderation. When sharpening, it is easy to go too far. You know when you've gone too far when the image starts to look garish or noise and graininess become noticeable. When you get to a point you like, it is a good idea to back off just a bit. It's always better to have a slightly soft image than one with too many artifacts.

Figure 8. Despite its name, the Unsharp Mask is very useful for sharpening the image. Experiment with Amount and Radius until you get a good result. Try toggling Preview on and off to see the before and after effects.