Hi Jorge,
Another idea, though more expensive, would be to use something like an OCS unit from Denkmeier (
www.denkmeier.com) to extend the focal point further out. Depending on the amount of inward focus you have available these types of unit will allow you to achieve focus on a camera that wouldn't normally focus.
I use the OCS unit (which is the "corrector" element from the front of the binoviewer) screwed straight into the 2" camera adapter and my scopes will reach focus with a Canon DSLR without moving (and somewhat de-stabilizing) the primary.
The OCS also has the benefit of coma correcting the field as well, but it does add a slight magnification factor to the focal length. Possibly a TV Paracorr or the like might also do the trick depending on your focusers available travel.
All that said, springs are cheaper though.
Regards,
Rob