Measuring master frames

In order to build up a catalogue of master dark, bias and flat frames...

Began by taking bias, dark and flat frames shortly after beginning cooling, in order to investigate the cooling ring which was seen in previous data. Upon taking frames it became evident that the cooling ring effect was only present on light frames, as no evidence could be seen in dark or bias frames.

Flat frames were taken by pointing the telescope at a large piece of evenly illuminated card, and taking exposures close to saturation. Shortly after turning the cooler on the frames were mostly just random noise, with a small smooth elliptical region in the centre [put a graphical example in, 4 at different times?]. Over time this smooth feature grew, and as it did dust rings became visible within it. Also a visible bow in the pixel values across the smooth region is seen, causing a vignetting effect (image appears darker at the edges). Note that this effect will change with focus, and so in the event of needing the refocusing the telescope, this step would need to be repeated.

By taking frames at regular time intervals, the time taken for the ring to disappear from images could then be found. It was observed that when taking dark frames with the telescope cover off, that ambient light could be seen in images. Therefore the cover was left on whilst taking dark frames.

Then master frames were taken in order to be used to accurately describe the background and improve thye signal to noise ratio of the final taken images.

-- DavidHadden - 03 Feb 2016

Physics WebpagesRHUL WebpagesCampus Connect • Royal Holloway, University of London, Egham, Surrey TW20 0EX; Tel/Fax +44 (0)1784 434455/437520

Topic revision: r2 - 03 Feb 2016 - DavidHadden

This site is powered by the TWiki collaboration platformCopyright © 2008-2018 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding RHUL Physics Department TWiki? Send feedback