This device is designed to correct the problem of a camera sensor being non-orthogonal with the optical axis of a telescope. If you have read the page about my field flattener, you'll be familiar with the issue of field curvature, which means that sometimes not all parts of an image are in focus at the same position of the focuser mechanism. This device deals with a similar issue in which the optimal position of focus is different for a different reason.

With all of the components that have to attach together it is almost impossible to avoid some imperfection in alignment. Whether it's some sag in the focus drawtube, an imperceptibly small bend in the threads of a flattener or filter wheel, or even an imperfect installation of the sensor in the camera body, the best images can only be created if adjustments are made to ensure the camera sensor is perfectly square to the telescope's optical axis.

The necessary adjustments can be made by tightening the appropriate conical adjustment screws around the edge of this device to eliminate any tilt that may be present. These adjustments are generally not ones that can be made based on simple observation of images, or even by measurement of the spacing. The tool I used to adjust is a plugin for the package 'N.I.N.A' called Hocus Focus, which takes a series of images and analyses the size of stars at various positions in the frame. By doing this it is able to optimise both the spacing from the flattener to ensure correct backfocus, and also to eliminate tilt by indicating which corners of the sensor are closer or farther from the telescope.

More information about this device can be found on the Gerd Neumann website.