Finally, in most cases, you're probably not going to want stars in every image on a particular shoot, so a lot of screwing and unscrewing the filter might be in order.
Star filters, like polarizing filters, can rotate, and spinning the filter rotates the star points around the light source, so the filter allows for a little bit of customization
This is a simple effect, a star quality that may enhance your image the way you want it. And actually this is at a fraction of the price for a regular star effect app.