This is a reducer designed specifically for flat field telescopes like the CDK. This reduces the f ratio of the CDK telescope 66%. The f/6.8 telescopes will be reduced to about f/4.5 and the f/8 telescope down to f/5.3.
There are two different models, one for the CDK12.5, CDK14, and CDK17; and one for the CDK20 and CDK24. Though these are optically identical, they are mechanically different. See chart in the image gallery for specific performance applications.