Parameters: Lens Diameter: 30 mm Focal Length: 120 mm Weight (include guider ring and dovetail): 250 g Back Focus: adjustable,（0~20 mm） Focuser Type: front part focuser Tube travel: 20 mm Dovetail includes 1/4″ screw hole.Lens Diameter: 30 mm Focal Length: 120 mm Weight (include guider ring and dovetail): 250 g Back Focus: adjustable,（0~20 mm） Focuser Type: front part focuser Tube travel: 20 mm Dovetail includes 1/4″ screw hole.