To get the most out of your tonian scope you really need to align or collimate the mirrors. It can take some time getting used to aligning both the secondary and primary mirrors and this short collimator can make it 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 ensure that the focal point reaches the best focus at the point from which the image will be viewed (the eyepiece or possibly a camera). Type: Monocular colour:Black Material:Aluminum alloy size:Calibration eyepiece: 1.24 inch Package Contents: 1 x Calibration eyepiece 1 x Dust cover