Hi All,
I was going to post this a few days ago, but thought I'd provide some lead time for Martin's image to get the recognition it deserves - very well done. While I've targeted this area
before, not at such a long focal length. Here's a collaborative effort between Alvin Jeng and I on an object that appears to always be a crowd pleaser and flavour of the month around here...the infamous
IC434 - Horsehead Nebula
The Horsehead nebula (also known as Barnard 33/IC434) is a tower of dark dust and gas which harbours the embryonic stages of young stars. The nebula is surrounded by energised hydrogen which glows vibrantly red. The Horsehead nebula resides approximately 1600 light years away.
The image is an LRGB composite totalling 10.3 hrs (L:170min;R,G,B:150min respectively). Alvin acquired the data on Lightbuckets 20" RCOS in Mayhill, NM. Total data collected was considerably more, but many subs where thrown away due to poor seeing and considerably nasty glare from Alnitak (see attached sub to view the dilemma). The glare streaks were most prevalent in the blue and luminance data. I wasn't too worried about the colour data as you can really blur this to remove these type of anomalies, but the luminance was a different situation. To reduce the impact, I blended the red channel (which was barely impacted by the glare) in to the luminance, then followed up carefully with the clone tool. Still nasty and time consuming, but minimised the impact somewhat. Unfortunately, dithering and data rejection didn't help very much in this situation. No Ha data for this target, just luminance. The Ha may have accentuated the curtain like streamers coming out of the background neb a little more, but I think I would have struggled with the RGB blend.
Slowly getting the hang of CCDStack and its functions...nice tool, but I've got some questions from those that use it...
When you perform a heavy deconvolution, I note that CCDStack draws a border around the image (probably around 15 or so pixel from the edge of the full frame). I can understand why it does this as any image misalignment could result in erroneous data for the algorithm to calculate. Hence the reason why cropping is important when using these types of functions. But what if you've already pre-cropped the image...is there a way you can tell the function to use the entire image? I end up with a dark line (maybe 2 or 3 pixels wide) around the border of the image - how do you get around this, other than bring it into PS and use the healing brush...eeekkk!
Do you need to normalise the individual R,G,B masters before creating a colour image? (this is probably in the manual, just haven't got that far yet). I'm really struggling to get the right colours out of CCDStack. It may not appear so in this image, but let me tell you, it took me considerable amount work to get the colours to what I thought were ok. The severe glare from Alnitak didn't help. I've never had to do this level of adjustment and tweaking in MaximDL. Perhaps its normal?? Just in case you didn't know, you can renormalise over and over as many times as you want or need. Doesn't alter the data (obviously the weights can change) - this was asked at AIC.
On the RGB combine (aka Color | create menu), do you leave the saturation at 1 or lower it accordingly. I find that stars have a magenta hue to them. I'm certain the G2V colour ratio's are correct. When the saturation is lowered they disappear, but so do the other rich colour tones you've worked hard to extract.
Sorry for all the questions, but I sense I'm not getting the maximum out of this tool.
Anyway, it was a bit of fun (correction - a nightmare) analysing and processing, but feel it came together well. All comments welcome, and last but not least, have a safe and joyful Christmas and New Year.
