The sharpness will come from the lens itself and your technique in using it. Filters can change the contrast between colors. A red filter will lighten reddish freckles, for example. If you want to accentuate reddish freckles you can use a green filter. Some people use a green filter to approximate the look of orthochromatic film. A blue filter can also be used to darken reddish skin markings/shadings. There are various shades of blue filters which can be used. Making a darker print can also show more details if you like that look. Contrasty lighting will also show more detail.