Tiffen 77mm North Star/FX Special Star Effect FilterI ordered mine from here.
This is a special effects filter used to jazz up photographs of shiny objects such as jewelry and other sparkly things.
It is not cheap, costing over $100 even from Chinese sellers on eBay, but its effects and really make an image "pop."
The filter screws on fine, and lets you spin the glass element with the filter firmly attached. This way you can rotate the sparkle effect to get the lines in the desired orientation.
This rotating end makes the fixed portion of the filter slimmer and a little harder to remove, if you have it well tightened.
I highly recommend for product shots, such as rings, that you use some sort of flash to really get the specular highlights to reflect back at the camera to produce the sparkle effect.
Other uses for the lens include the sparkle on a stream and the chrome on a hot rod.
There are many star filters with multiple points, and most of them are a lot cheaper than this filter. But, their results are a little plain and average. This filter stands out from the rest with its star pattern like that of the Northern Star (hence the name of the filter) and I highly recommend it to have your shiny photos stand out from the competition.
Following are some sample photos to demonstrate the power of this type of lens and some general uses which will likely yield good results. If you shoot things like these, then this lens may be a good one to think about adding to your camera bag.