I’ve been meaning to capture a new version of this nebula as the previous one, done on the Astrotrac exhibited quite pronounced trailing. This will be one of my final images done with the WO Zenithstar 70 as I’ve purchased an ex-demo Takahashi Baby-Q (FSQ85-EDX). I’ve enjoyed working with the Zenithstar and I’ve learnt a lot in the years of using it but the time has come to upgrade to something with rather better colour correction and a flatter field.
While at Kelling Heath in October I took advantage of the darker skies to leave the scope collecting data until dawn of this area just to the west of Rigel in Orion. The Witch Head is very faint and being low in the southern sky is swamped by light pollution at home. This is a re-processed version of the image that appeared on the club Facebook page some time ago and I was planning to add more data over the course of the winter. However, having just purchased a new refractor this isn’t going to happen and I’ll start over with the new telescope.
Even from Kelling there were severe light pollution gradients on these images which I removed using Pixinsight. The club’s dark skies site at Haw Wood on the Suffolk coast will probably be the location of choice for any new attempt.
I came upon this object whilst looking at my copy of Sue French’s book Deep Sky Wonders. I was looking for a suitable photography target and this appealed due to it’s large apparent size, high altitude and relative obscurity. Located on the Cassiopeia / Andromeda border it also features a subject that engages me; dust.
Dust can be tricky to photograph as it doesn’t emit any light of it’s own. All you get are reflections from nearby starlight or absorption of light from more distant stars. This means that it’s often dark and usually very faint so you need a reasonable sky quality and long exposures to capture it.
With a rural UK sky and only 150 minutes total exposure (in 10 minute subframes), faint detail is still elusive in this image. This is definitely one to revisit from a darker sky and a lot more exposure.
This is another image from the beginning of last week and I’ve reprocessed this from the version that I posted on the Breckland Facebook page. The background stars are a little less harsh, I’ve increased the contrast in the nebula and it’s a slightly closer crop. This is nine 10 minute subframes.
NGC 1499 in Perseus is a large, bright emission nebula created by the bright blue star Xi Persei irradiating a hydrogen gas cloud with UV. The brightest part of the nebula spans 5 degrees on the sky and just fits on the sensor of my QHY9 when used with my Zenithstar 70 and 0.8x reducer.
This is 110 minutes of 10 minute frames captured on Tuesday evening, processed with Pixinsight.
Friday night was clear until the moon rose at about midnight so I took the opportunity to add another 2 hours of data to that I’ve already collected on NGC 7000. The mount tracked well despite the brisk breeze and all 12 10 minute frames were good.
After calibration and stacking in Maxim DL, I opened Pixinsight for further processing. I’ve been playing with the Masked Stretch script but this has an unfortunate side effect of emphasizing the blue halos around bright stars and I haven’t worked out how to reduce this effect yet, so I used a basic histogram stretch. This was followed by an HDRMultiscaleTransform to push down some of the highlights and a LocalHistogramEqualisation (using a mask to protect the stars) to increase the contrast on dark structures. A morphological transform was used to reduce the intensity of the field stars.
After this, a TGVDenoise and saturation curves application completed the image.
The autumn event at Kelling Heath has come and gone for another year. Friday evening was cloudy meaning I could catch up on some sleep. Saturday was partly cloudy, clearing for an hour and then it clouded over completely until early on the Sunday. I’d booked an extra night for the Sunday and this turned out to be the best night with clear skies from dusk until dawn.
As soon as it was dark enough I started taking pictures of Sh2-155 in Cepheus again as I want to complete the right hand side of the Cepheus mosaic. Once Orion was high enough I started a mosaic of the Witches Head and left CCD Commander taking images until dawn while I caught up on some more sleep.
When processing, I decided to try something different and followed a workflow tutorial on the Pixinsight website for dynamic range compression. This uses HDRMultiscale as usual but replaces the stars with ones generated using the masked stretch script.
The initial result is here. Next step will be to add in the remaining data from Saturday evening and then combine the frames into the Cepheus mosaic.
No complaints about the British weather this weekend. The clear nights at the Haw Wood star party were a treat. This weekend, with the moon waning, both Friday and Saturday night were forecast to be clear.
Friday night had some cloud drifting through from time to time. I was also trying to get to grips with CCD Commander before it’s trial license expired so I had some work to do. In the end, I gathered about 3 hours 40 minutes worth of 10 minute sub frames of this pretty pairing in Cepheus.
An initial look at the data looked promising. I did have a problem with the flat field frames though. These were taken at dawn by CCD Commander but I’d turned the coolers off beforehand. As a result, the flat wasn’t a good match for the light frames so I needed to redo these. I haven’t measured the bias levels at different temperatures but I suspect that it varies wildly.
On Saturday I setup early for dusk flats then waited for dark. During the day I’d taken the step of installing the new NoMachine remote control software, both on my Netbook and main PC. As the Netbook is Windows 7 Starter edition, I don’t have the option of running Remote Desktop Protocol (RDP). The new software has the advantage over the popular VNC of passing sound to the client PC. This should enable me to hear audible alerts from Maxim inside the house.
I collected a further 3 hours of data. taking me up to 6 hours 30 minutes. This is the longest I’ve ever exposed on a single target. The bright blue foreground stars create a severe challenge for the doublet Zenithstar which shows significant colour fringing.
The original intention with this picture was to take 5 hours of sub frames of the Cave nebula (Caldwell 9), aka Sh2-155 in Cepheus. However, a problem with the focusser meant that after the first 90 minutes the remaining images were offset in RA. Fortunately, there was enough overlap to enable me to join the images in a wide field mosaic. The bright cluster bottom left is M52.
There’s some residual light pollution down the centre of the image. This is very hard to deal with in mosaics. Also, there’s a lot more noise in the right hand side due to the relative lack of exposures.