The Unsharp Mask command in the Sharpen submenu in the Effect menu focuses blurry images by increasing the contrast of adjacent pixels. This effect is raster-based and uses the document’s raster effects settings whenever you apply the effect to a vector graphic.

Unsharp Mask

Finds the areas in the image where significant color changes occur and sharpens them. Use the Unsharp Mask filter to adjust the contrast of edge detail and produce a lighter and darker line on each side of the edge. This emphasizes the edge and creates the illusion of a sharper image.