RC Telescopes by GSO have a long back focus making this system ideal for the use of off-axis-guiders and / or focal reducers. But in standard use, the long back focus may have problematic side effects: In many applications, the focuser must be extended totally and it still needs extension then. This is neither optically nor mechanically a recommendable solution.The GSO extension tubes are placed between telescope and focuserThe advantages of this solution can bee seen clearly: The focuser is always in an optimal position and needs no further extesion with a sometimes problematic lever arm. The free aperture is significantly larger.Technical details:-- Extension tube suitable for Officina Stellare and GSO RCs from 6"-8" aperture (DeltaOptical, Binorum etc)-- M90x1 threads (female on telescope and male on camera side)-- Optical length: 50mm