This is a reducer designed specifically for flat field telescopes like the CDK. This reduces the f ratio of the CDK telescope 66%. The CDK12.5 f/8 telescope will be reduced down to f/5.3. The CDK14 will be f/4.8 and for CDK17 f/6.8 will be reduced to f/4.5
**NOTE - 125166 adapter is compatible with CDK17 that have 10.24" back focus. CDK17 with 8.81" back focus will use the 200166 focal reducer. See instruction manual for details.