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Audine CCD camera with Newton telescope 165/1145



14 October 2009
After 2 weeks of rain and clouds, the good weather comes back on Netherlands ! Perfect night, no clouds, no Moon.
Bubble nebula = NGC7635
Composition of 60 x 20 sec exposures, offset, dark and flat corrected with IRIS v5.57
Sigma clipping addition, personal software based on CFITSIO

The slightly noisy aspects come from the logarithms used in the processing, to avoid saturation of the bright parts of the nebulae. In both cases, the signal-to-noise ratio was quite good. Limit magnitude is now around 17.7 according to Astrometrica : as compared to my previous M27 picture (see below), improvement in magnitude comes from (1) sky more transparent with less cirrus clouds (2) higher declination of observed object (3) longer exposure times for individual acquisitions, that reduces read-out noise.


 IC 1470, small nebula in Cassiopea
Composition of 36 x 20 sec exposures, same treatment as above



18 September 2009

The following pictures are combinations of a large number of 10 sec acquisitions. The current stability of the mount does not allow much longer times.
Limiting magnitude is 17.0 (checked with Astrometrica / USNO-B 1.0).

 Dumbell nebula = M27
Composition of 80 x 10 sec exposures, offset, dark and flat corrected with IRIS v5.57
Sigma clipping addition, personal software based on CFITSIO


 NGC 7008, planetary nebula in Cygnus
Composition of 49 x 10 sec exposures, same treatment as above



16 September 2009 = oriented noise features due to bad dark correction

Both pictures below show some background noise with oriented features.

 North America nebula
Composition of 90 x 10 sec exposures, offset, dark and flat corrected with IRIS v5.57


 Veil nebula in Cygnus, NGC 6960
Composition of 120 x 10 sec exposures, offset, dark and flat corrected with IRIS v5.57


This kind of defect comes from the fact that the image used to correct dark noise (10 sec exposure with closed shutter) was taken another evening. Probably, the camera was in different temperature conditions and I could not make properly the dark correction. The pictures are obtained by adding a lot of shortly exposed images (I use short exposures to remove effect of mount vibrations during acquisition). There is also a small spatial shift between all added images, due to the slow drift of the unperfectly aligned equatorial mount.

The combination of these three factors : a lot of images + a slow drift + bad dark correction, creates the oriented noisy features. Due to bad dark correction, a residual constant noise pattern which remains in every image, and when you add everything this creates the noisy features which are oriented in the direction of the mount drift.

To avoid this in the future I will have to improve the dark correction. So I will take offset + dark measurements every night of observation ! The best would be to take dark measurements before and after the acquisitions, with the idea of using the average dark for the treatment of the final pictures. I suppose that this will remove all effects of a linear temperature drift, so the correction will be better.