wisecrafter wrote:
I have a "Hoya special effect filters" users instructions pamphlet, and Chapjon is correct, it is a Center Spot. The center spot is a close-up lens of approximately +2 diopters with a hole cut in the center.
As a side note, CS also designates Color-spot. You can tell if it is a Color-Spot because it will have a hole in the center and comes in Red, Green, Yellow, and Gray.
Here is the heading for the first filter pictured below and currently up for auction on ebay. It is labeled CS on the ring. Hopefully you can see it:
The second filter is a Center Spot found on Google Images. It is labeled Center-Spot on the ring. Hopefully you can see it.