I added the PlaneWave Delta T Heater System to my CDK400 System. The CDK 17 has ambient temperature sensors, temperature sensors on the primary mirror backplate, the primary mirror, and the secondary mirror. Those components are also pre-wired with electronic heating elements. The Delta T system monitors the temperature of all these components and if the difference between them and ambient temperature is such that the optics are in danger of forming dew, it will activate the heating elements and keep them dew-free. The CDK 17 also has a large number of fans that help it reach ambient temperature rapidly and can remove the boundary layer of air on the primary mirror that can distort images.