When installing ESATTO 3" in a telescope with a long travel focuser (such as those usually found on refractors), it is necessary to take into account the lower travel of ESATTO 3" since it's a micrometric focuser. For this reason we have designed this 40mm extension that can be installed between ESATTO 3" and the telescope tube. A precise dovetail coupling system with 3 screws set at 120° allows you to manually rotate the focuser.