Hoya Color-spot filters have a clear spot in the center which allows the portrayal of an object in a different 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