Blog Image

Earthshine blog

"Earthshine blog"

A blog about a telescopic system at the Mauna Loa Observatory on Hawaii to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

Square aperture for CCD

Mechanical design Posted on Nov 15, 2011 05:49PM

It has become evident that the square aperture in front of the CCD chip can shift – or rather, that the CCD camera can shift relative to the mask. The mask is present to help the frame-transfer procedure by shading the part of the frame that holds the transferred image during readout. If the CCD was not half-shielded the ‘smearing effect’ would occur due to illumination during readout. The mask is a set of adjustable blades, apparently that are fixed wrt the telescope body. The CCD itself is held to the body by a thread and the correct position is indicated by two steel pins that should touch, visible from the outside. It has occurred that the CCD has ‘unwound’ and this caused ‘dark corners’ to appear in the images. The camera had indeed ‘unwound’ a bit and was rotated back into proper position.

Following that incident a ‘black bar’ has appeared in the side of the image – perhaps due to slippage of the camera wrt the blades, or the blades’ motion.

The issue is further discussed here.



Historic material on Earthshine

Links to sites and software Posted on Nov 15, 2011 05:33PM

Leonardo da Vinci’s notebooks: http://www.fromoldbooks.org/Richter-NotebooksOfLeonardo/section-14/item-902.html

A reference to Humboldt in 1774: http://www.britastro.org/journal/pdf/120-4forum.pdf also, Kepler and Galileo.