The Cokin Center Spot Red filter has a clear spot in the center and allows for the portrayal of an object in a red colored surrounding. The filter effect is directly influenced by the f-stop and the focal length. The transformation is softer with wider apertures. The size of the clear circular area increases relatively with the selection of longer focal lengths.
The exposure determination should be done without the filter. If the camera has the capability of spot-metering, then one can measure with the filter in place.
This filter measures 85 x 85mm and fits the Cokin P series holder.