Earthshine blog

Earthshine blog

"Earthshine blog"

A blog about a system to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

Ghost and Dragging

Optical designPosted by Daddy-o May 21, 2013 07:58AM
Here are example sof a 'ghost' and 'dragging':


The dragging is due to no shutter being used - i.e. readout was only way to terminate exposure and hence frame was illuminated as the image was shifted to the 'hidden register' We hav a frame-transfer camera. The image is from the test phase in Lund and no shutter was installed then.

The BS ghost is faintly vissible: It is a copy of the BS and the lower cusp is seen poking out slightly down and to the left of the real BS. This was due to the CCD camera being aligned almost perfectly along the optical axis of the system - the ghost arises as the shiny CCD surface reflects light back into the optical system and reflections are produced at all optical surfaces - the back of the second secondary lens, the front of the second secondary lens, the back of the first secondary lens, the front of the first secondary lens and the back of the primary objective and its various surfaces. At MLO the camera was tilted at an angle so that the reflection from the CCD did not go back up the system. This tilting did not appear to have any adverse effects on focus etc.

Images from lab hard disc recovered from MLO.

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