2" CCD Spacer: A CCD Spacer that accepts a standard 2" barrel. These come in lengths of 3.8", 3.3" and 2.8". The back focus of the CDK20 is 5.8" from the racked in focuser and the focuser has 1.3" of travel. To choose the correct spacer, you want the back focus of your camera plus path length of any other accessory plus the CCD spacer to be between 4.8 and 5.8".
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