Features: 1.25 inch calibration eyepiece is of short size, made from aluminum alloy and finished by CNC manufacturing. Used to calibrate the optical axis of a reflector, put the collimation eyepiecre into the tube. Make sure the black spot is in the center of 2 lines of collimation eyepiece. Please adjust the screws if it is not in the center, in this way, you will collimate sucessfully. A wonderful accessory for both photography and astronomy lovers. Specifications: Condition: Brand New Material: Aluminium Alloy Color: Black Caliber Diameter: 1.25in * Suitable for reflecting telescope length: Approx. 64 mm / 2.52 in Diameter: Approx. 35 mm / 1.38 in Weight: Approx. 92 g Package List: 1 * Eyepiece Package List 11.25 inch calibration eyepiece is of short size, made from aluminum alloy and finished by CNC manufacturing. 2Used to calibrate the optical axis of a reflector, put the collimation eyepiecre into the tube. 3Make sure the black spot is in the center of 2 lines of collimation eyepiece. 4Please adjust the screws if it is not in the center, in this way, you will collimate sucessfully. 5A wonderful accessory for both photography and astronomy lovers.