set2: 1 x Short calibration eyepiece + 1 x Long Calibration Eyepiece Economical collimation tool ensures that your reflector telescope's optics are in precise alignment. Combination 5inch long sight tube and 1.25inch Cheshire eyepiece. For aligning optics of Newtonian reflectors, Peephole in top and crosshairs at bottom enable precise optical centering. Compatible with 1.25inch telescope focusers or 2inch focusers with a step-down adapter for using 1.25inch accessories To get the most out of your Newtonian scope you really need to align or collimate the mirrors. It can take some time used to aligning both the secondary and primary mirrors and this short collimator can much easier. The short collimator for mirror (reflector) telescopes has a 45 degree plate for easier visual accuracy. Collimation is the alignment of elements inside an optical system like a telescope. Colimating a telescope consists of adjusting the tilt and position of the mirrors and lenses to that the point reaches optimum focus at the point from Size: 4.2 x 4.2 x 15.2cm which the image be viewed (the eyepiece or possibly a camera). colour:black Material:Aluminum alloy Package Contents: 1 x Short calibration eyepiece 1 x Long Calibration Eyepiece 2 x boxes 2 x opp bag Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.