Patent ID: 7259910

Claim:
A focal device for a telescope comprising: an eyepiece clamping member tightened by a tightening ring to fix an eyepiece with its one end and a focus adjusting tube fixed with the other end of said eyepiece clamping member; said focus adjusting tube having male threads on its exterior wall and limited to move axially only by a direction restricting member and able to extend into the inner side of said eyepiece tube with its one end; a focus adjusting ring formed as a hollow cylinder and having female threads in its interior wall for engaging with said male threads of said focus adjusting tube to let said focus adjusting tube pass through and limit said focus adjusting ring to rotate only and unable to shift axially; said focus adjusting ring rotated clockwise or counterclockwise to activate said focus adjusting tube to move axially so that the axial force line may overlap totally with the eyepiece axial line and the telescope axial line to acquire a perfect precise focusing; wherein said focus adjusting tube possesses plural axial projections spaced apart equidistantly on its exterior surface, each said projection having male threads; said direction restricting member is fixed in said main body, having direction restricting grooves coordinating to said axial projections respectively so that said focus adjusting tube can only shift axially; wherein a fixing washer is confined between said main body and said direction restricting member, unable to shift axially, having plural holes spaced apart around; said focus adjusting ring has a shrinking neck at its one end and threaded holes in the annular surface of said shrinking neck, said threaded holes coordinating to said holes of said fixing washer so that bolts can pass through them to keep said fixing washer and said focus adjusting ring fixed together, enabling said focus adjusting ring to rotate only but not shift axially.