jase
15-11-2008, 11:57 AM
Hi All,
I’ve been sitting on this image for sometime and believe now would be an appropriate time to release it. I produced this image exclusively for Lightbuckets (http://www.lightbuckets.com) to display at the AIC2008 conference which is presently being held in San Jose, California. I was looking for something rather unique and intriguing. So without further ado, I’m pleased to present IC4633 in Apus (http://cosmicphotos.com/gallery/image.php?fld_image_id=161&fld_album_id=12).
About the target;
IC4633 is a spiral galaxy (Sc type, mag. 13) located in the constellation Apus. The galaxy is almost obscured by a vast and very faint interstellar nebulosity known as Integrated Flux Nebulae (IFN). This type of nebulae is illuminated not by a single star, but the energy from the integrated flux of all stars in the Milky Way. The nebula consists of hydrogen, dust particles, carbon monoxide amongst other elements and has been designated MW9.
Some words on the image;
Something for those that like targets off the beaten track. The image is an LLRGB composite with a total exposure time of 9 hours (L:280min,R:90min,G:80min,B:90min). It was acquired using Lightbucket’s 14.5” RC (~3315mm FL) located in Pingelly, WA. Despite the ample planning, dark skies and instrument utilised, I really had a hard time with this image. At Pingelly, IC4633 crosses the meridian at 44.5 degrees which made obtaining good resolution difficult – the further south you’re located, the better. This took additional planning where I only acquired the luminance data over successive nights when the object was at the highest point. I feel the stars reflect the lack of resolution, considering they appear rather soft...in some cases looks like a guiding issue, even though there wasn't one! The luminance data was combined using Sigma Reject in MaximDL and placed through two iterations of deconvolution using CCDSharp. The IFN is faint, so realised it needed to be stretched reasonably hard to extract it’s wispy features. Having played around with curves to stretch the data, I was not obtaining the desired result. I used DDP, something I don’t often do to achieve the task, and ensuring no data was clipped in the process. The reasoning behind the DDP decision was also the management of stellar profiles in one-step. I duplicated the original luminance frame and stretch it using conventional level and curves to a point where the galaxies showed good structure with no clipping. Selective processing through PS layers was invoked to combine the two. Subtle intensity differences between the layers were addressed with PS brighten/contrast control. Layers were flattened and relayered again with RGB data to manage detail and colour saturation. Talking RGB data, I struggled with getting it looking “correct”. While the flats applied were correct for the PIR angle, I experienced colour shifts between the filtered exposures, perhaps due to the low altitude. This resulted in mottling which is visible in the presented image. While I’ve chased this effect before in other images using a Gaussian blur mask, I found it too much of a tedious job when dealing with a background that isn’t uniformly dark due to the IFN. There maybe other ways of dealing with the issue, but I have yet to come across one which is effective. I reduced the impact of the mottling with a low frequency invert mask created in noise reduction PS plug-in Neatimage with a reduced fill effect, blended as colour. Not ideal, but worked ok. Always willing to try something different to see if the step leads to improvements. Being low in the sky (even at its highest point), the blue channel could have done with considerably more data to compensate for atmospheric extinction. I did however apply a multiplication factor which appeared to restore the weight, be it subtly. The dusty characteristics of the IFN are perhaps too colour saturated, but think the effect works well with the contrasting blue hue of the spiral galaxy. This is a fascinating region in which I’ve previously targeted with the FSQ, but have insufficient data to work with. Maybe next season, I’ll complete the mission if not distracted to move down the target list for the season in the meantime.
I’d like to thank Steve of Lightbuckets for providing the opportunity to nail this target and permission to post on the website.
Thanks for checking it out, hope you like it. As always, all comments welcome.
Cheers
I’ve been sitting on this image for sometime and believe now would be an appropriate time to release it. I produced this image exclusively for Lightbuckets (http://www.lightbuckets.com) to display at the AIC2008 conference which is presently being held in San Jose, California. I was looking for something rather unique and intriguing. So without further ado, I’m pleased to present IC4633 in Apus (http://cosmicphotos.com/gallery/image.php?fld_image_id=161&fld_album_id=12).
About the target;
IC4633 is a spiral galaxy (Sc type, mag. 13) located in the constellation Apus. The galaxy is almost obscured by a vast and very faint interstellar nebulosity known as Integrated Flux Nebulae (IFN). This type of nebulae is illuminated not by a single star, but the energy from the integrated flux of all stars in the Milky Way. The nebula consists of hydrogen, dust particles, carbon monoxide amongst other elements and has been designated MW9.
Some words on the image;
Something for those that like targets off the beaten track. The image is an LLRGB composite with a total exposure time of 9 hours (L:280min,R:90min,G:80min,B:90min). It was acquired using Lightbucket’s 14.5” RC (~3315mm FL) located in Pingelly, WA. Despite the ample planning, dark skies and instrument utilised, I really had a hard time with this image. At Pingelly, IC4633 crosses the meridian at 44.5 degrees which made obtaining good resolution difficult – the further south you’re located, the better. This took additional planning where I only acquired the luminance data over successive nights when the object was at the highest point. I feel the stars reflect the lack of resolution, considering they appear rather soft...in some cases looks like a guiding issue, even though there wasn't one! The luminance data was combined using Sigma Reject in MaximDL and placed through two iterations of deconvolution using CCDSharp. The IFN is faint, so realised it needed to be stretched reasonably hard to extract it’s wispy features. Having played around with curves to stretch the data, I was not obtaining the desired result. I used DDP, something I don’t often do to achieve the task, and ensuring no data was clipped in the process. The reasoning behind the DDP decision was also the management of stellar profiles in one-step. I duplicated the original luminance frame and stretch it using conventional level and curves to a point where the galaxies showed good structure with no clipping. Selective processing through PS layers was invoked to combine the two. Subtle intensity differences between the layers were addressed with PS brighten/contrast control. Layers were flattened and relayered again with RGB data to manage detail and colour saturation. Talking RGB data, I struggled with getting it looking “correct”. While the flats applied were correct for the PIR angle, I experienced colour shifts between the filtered exposures, perhaps due to the low altitude. This resulted in mottling which is visible in the presented image. While I’ve chased this effect before in other images using a Gaussian blur mask, I found it too much of a tedious job when dealing with a background that isn’t uniformly dark due to the IFN. There maybe other ways of dealing with the issue, but I have yet to come across one which is effective. I reduced the impact of the mottling with a low frequency invert mask created in noise reduction PS plug-in Neatimage with a reduced fill effect, blended as colour. Not ideal, but worked ok. Always willing to try something different to see if the step leads to improvements. Being low in the sky (even at its highest point), the blue channel could have done with considerably more data to compensate for atmospheric extinction. I did however apply a multiplication factor which appeared to restore the weight, be it subtly. The dusty characteristics of the IFN are perhaps too colour saturated, but think the effect works well with the contrasting blue hue of the spiral galaxy. This is a fascinating region in which I’ve previously targeted with the FSQ, but have insufficient data to work with. Maybe next season, I’ll complete the mission if not distracted to move down the target list for the season in the meantime.
I’d like to thank Steve of Lightbuckets for providing the opportunity to nail this target and permission to post on the website.
Thanks for checking it out, hope you like it. As always, all comments welcome.
Cheers