When Roland Christen (founder of Astro-Physics, Inc) was asked why AP did not offer carbon fiber tubes on their APOs, Roland said that a three element APO lens experiences a focal length decrease as temperature drops. The rate of focal length shrinkage of the lens is very close to the shrinkage experienced by the aluminum tubes they use on their scopes. As a result, there is only a small focal plane shift with dropping temps with their scopes. I do not remember which one shrinks more. When carbon fiber is used as the OTA material, it does not shrink and, as a result, there is more focal plane shift with carbon fiber tubes. So, no carbon fiber at AP.