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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.

Shutter dissapointment – part II: The Rubbing It In

Shutters Posted on Oct 13, 2011 17:30

The Canon shutters we tested – see here and here, seems better than the Uniblitz shutter we have – at a fraction of the cost. For very few dollars we could have had a substantially more reliable shutter.

Another problem

Shutters Posted on Oct 13, 2011 17:19

We have come across another problem with the shutter: Not only is it variable when it shouldn’t be – i.e. we have complete frame dropouts and we have a spread in observed counts from sources that are constant – stars at short exposure time excluded here due to scintillation – but we also now have examples of FITS file headers that show the measured to exposure time to be 0.000000000000001s when it is patently not – for instance, the image is fine and shows a well-exposed Moon.

This limits our possibility to use the ‘not simultaneous’ modes of observing – i.e. BBSO and modified BBSO.

Calculated flat field

Bias and Flat fields Posted on Oct 13, 2011 16:02

Flat field calculated using Chae’s method. It is based on 115 lunar images ‘dithered’ randomly around a central point. The dust speks near the middle are recognized from conventional FFs. The two diagonal stripes are also recognized as part of this CCDs extraordinarily strong fixed-pattern. The gradient from blue to pink and white corresponds to 2%. The image is based on B-band images from the night JD2455847.

It turns out that ‘slopes’ in this method has to do with the normalization of the source intensity – the method depends on the source being constant, but the source is not constant if it is partially on the dge of the image frame, is it? We are working on this.