Another tip....never use the sharpen filter on a scan. Instead, use the "Unsharpen Mask". If you are using Photoshop, set the Radius to .3, the Threshold to 8, then move the slider up till you get the desired sharpness.
Okay, now, if you are using Photoshop, once you have finished editing the picture, use the sharpen tool to accent certain features to make the picture look sharper than it really is. I set the strength to 30%, and use a brush that is small....maybe 15 pixels, and I use a hard brush. I will apply this brush to the model's eyes, hair, nose, lips, teeth, nipples, belly button, any jewelry she's wearing, fingers, toes, and her vagina. By doing this, it will make the picture look sharp.