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.
You may find a blue filter a bit much. As above, a green filter may be a better bet. But a 100 ISO film or slower, a sharp lens and a little over development might be what we're seeing in your samples.
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