RBA & AF Astrophotography

Comet Garradd and the Coat Hanger

Posted: September 3rd, 2011



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Sweeping through planet Earth's night sky, on September 3rd, 2001, Comet Garradd (C/2009 P1) visited this lovely star field along the Milky Way in the constellation Vulpecula. Suggestively oriented, the colorful skyscape features stars in the asterism known as the Coat Hanger with the comet's tail pointing toward the southeast. Also known as Al Sufi's Cluster, the Coat Hanger itself is likely just a chance alignment and not a cluster of related stars. But compact open star cluster NGC 6802 does grace the field of view just right of the Coat Hanger, near the edge of the frame. Below naked eye visibility but approaching 7th magnitude in brightness, Comet Garradd has been a good target for binoculars and small telescopes. Still, bright moonlit skies this week will make the comet harder to spot. (Text from APOD).

Here's a different composition framing just the comet and the Coat Hanger:

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Circumpolar at the DARC Observatory

Posted: August 8th, 2011



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Here's a circumpolar image I captured at the DARC observatory on a fine summer night.

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The Dolphin

Posted: July 3rd, 2011



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This is a 2 pane mosaic of the Dolphin asterism, which I photographed attending a request from a loved one during our attendance to the Golden State Star Party 2011.

Besides documenting this area of the sky and this famous and friendly asterism, there are not many significant structures to feature in this image. In the large version you can see PGC 65060, a spiral galaxy between ι Del and ε Del, and some faint nebulosity between 12 and 1 o'clock.

Here's a version with the asterism and star names:

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Lyra: One million stars... and one ring

Posted: June 15th, 2011



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Here's the constellation Lyra. And yes, there's over 1 million individual stars in the image (from an automated count on the uncompressed image). Unfortunately you won't be able to split many stars in the image, but with a bit of effort and knowing where to look, you'd be able to "see" the famous Ring nebula!

The brightest star in the image is Vega, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, with a 0.03 magnitude. It's also one of the vertexes of the famous Summer Triangle asterism.

Here's a small version with the Lyra asterism and star names:

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The Big Dipper

Posted: June 14th, 2011



Here is a 24 panes mosaic image covering the vast area "taken" by the well known Big Dipper in Ursa Major. possibly the most famous asterism in the Northern sky.

It was taken during 7 nights at DARC between May 25 and June 1st. It was the"first light" of my FSQ after cleaning the front lens. Processed with PixInsight, Registar (more as an auxiliary tool, not really on the data) and Photoshop.

I know it's not the typical "in your face" image, but there's something I like about these rarely seen (in photographs) "high res" vast fields, where not one single object captures your undivided attention. Also, as Wolfgang Promper said: It's the fact that it is a deep image and still you can relate to what you see when looking to the sky unaided.

As for the dusty background, as usual, I give a high percentage in its accuracy, but not necessarily for each and every single detail.

Surf around and find the "hidden" owl ;-)

Here's a small version with the asterism, star labels and also labels for all the Messier objects in the image:

I personally had a lot of fun doing things like finding Hickson 50 (it is there, just not an easy catch, and when you find it, it's just a blur!) and other objects (lots of cool NGCs and a few popular Messiers of course)...

I hope you enjoy it!



Little Dipper

Posted: May 12th, 2011




I started this project in January, from the Pinar de Araceil in Spain, during two incredibly freezing nights, imaging only between 4:30 and 6am. After that, I captured more data very slowly, as I only wanted to capture data when the bowl of the constellation was high in the sky, and that could only be at the time all you want to do is pack and go home.

Finally, during several nights in April I was able to finish all frames that included the actual asterism, and in 4 more nights in May (all at the DARC Observatory), I completed the areas above and below it, to become the 20 frames (4x5) mosaic that you can now see.

The image at first doesn't seem to impact very much. It is after all mainly dominated by stars and some faint galactic cirrus in the background. Still, I had this project in mind for many months, as I really wanted to see this "small" constellation at a better resolution and depth than what I had been able to see before, and I was just patiently waiting for the right time to capture it.

Down here you can see the image with asterism and star names:






The Volcano Nebula (IFN, M81 and M82)

Posted: May 4th, 2011



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This image covers a "small" area of the mosaic I did in 2010, but in this case, spending more hours on this particular area, and preserving its original resolution.

The field of view shows part of the area of IFN that Steve Mandel named The Volcano Nebula near the famous M81 and M82 galaxies.

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One star, many stars (M13)

Posted: May 4th, 2011



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I spent the nights from April 28 to May 1st at DARC, again :-)

Besides finishing my Little Dipper mosaic and a few other things, at some point late during the last session but still with some night time left, I decided to go for an unusual framing of M13. Unfortunately, after three wonderful nights, that night, the end of this night wasn't so good, and in fact I ended up throwing away all the shots.

Therefore, on May 3rd, I went up to Henry Coe State Park (one of the parks that is scheduled to close in September 2011, sadly) to at least get some color data.

And after that, the next day, on Wednesday (May 4th) I got some courage and went back to DARC, this time capturing about 20x10 minutes of luminance and a bit more RGB. In the end I only used the RGBs from DARC because the ones from Coe seemed a tad out of focus.

Now, about the image I am presenting here, the star in the lower left is Eta Herculis, and the globular cluster is, of course, M13.. The background variations are exaggerated, but they're not artifacts. Still, there's a round dark patch to the right of M13 that, although I haven't investigated it, it looks like it might be a badly deflated dust mote.

People who are familiar with this object and astrophotography would say that the FSQ is not the right telescope to use for this object, M13. Well, yes, they are right. However, I think I managed to capture an interesting image that isn't just centered on the famous globular cluster, and provide a unique view, if not of this object, at least of the area in the sky where it sits.

 



Coma Berenices

Posted: May 2nd, 2011



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Here's an image of Coma Berenices, also known as Melotte 111.

It was after seeing this image that I decided to get a new set of filters to avoid the huge halos around the bright stars - which I did just a few weeks later.

Also, there's a few strange things in this image. Most stars seem to have a rather pronounced color ring, and the brightest stars look quite blurred. One could think this blurry effect was an effect of the post-processing, but it's not.

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Virgo Cluster Deep Widefield

Posted: March 18th, 2011




GOALS
AND PRESENTATION

It would be easy to produce a "standard looking" image with this data. Truly minimal processing would be required, but in this case and at this time, for me that wouldn't be nearly as fun neither challenging.

The goals when producing this image were very precise. Just a glance at the image should reveal what these goals are, and I am somewhat satisfied with the results - meaning the goals were achieved to an extent. Clearly the main goal was to reveal any subtle and faint data - the data that typically sits right above the noise. A secondary goal was to do this while containing galaxy brightness and at the same time, being able to bring out small scale details in such galaxies.
 
To enhance details in the galaxies, a dynamic range compression process was applied to reduce brightness in the larger galaxies, as well as wavelets-based HDR enhancements. Preserving background illumination was accomplished by very careful gradient reduction and further non-selective histogram adjustments.

There may be some people who find all the "dust" in the background distracting, or the small details in the galaxies somewhat the result of processing and not a "natural" depiction of the field, but ...In order to appreciate this image you need to understand the goals set for it, then conclude whether those goals were met or not, rather than whether you would have aimed for different goals.

DETAILS IN THE DUST

In order to better see the "dusty background" I have also prepared a monochrome image that you can see here:

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It may be surprising to see an image with all this dusty appearance in this direction, out of the galactic plane.  To be honest, that is not for me to judge, but this is what came out of my data, and the processing involved was as careful as possible. Data capture wasn't perfect but all the data was taken from the same location, during the same hours on three different nights, and on nights I was very discriminative as to whether  I should capture data for this project or not: all nights displayed an SQM reading of magnitude 21.7 or higher at the zenith at some point during the session, and were all consistently above 21.5 at any time.

Although most of the dust above the background you see in this image is likely from our own galaxy, if you look closely, on top of NGC 4435 (the "eyes"), you may see a thick faint tail moving towards 10-11 o'clock, and that is most likely pulled from that galaxy, not a foreground cloud. The "1" arrow in the image below points to this area. There's also some even fainter strikes visible (barely) going from M86 towards NGC 4435. The lines to the right of the "2" in the image show where these strikes are happening. You will need to go back to the larger version of the above image to better discern them (the green lines in the image below are covering the most visible strikes).

There's also some intergalactic "fluff" - though very diffuse in the image - from M87 to NGC 4461 and NGC 4473. And of course, the well-known interaction between IC 3481 and IC 3483 is clearly visible towards the bottom of the image:

Other than that, I personally cannot tell whether other faint signal is intergalactic, it belongs to our Milky Way or, suffice to say, might be an enhanced artifact during capture or processing.

BACKGROUND MODELING

The hardest part in processing this image was the gradient removal process. It's not that the gradients were complicated or severe. In fact, they were very smooth and subtle, thanks to the dark skies of the DARC Observatory, and if I hadn't gone after the fainter signal, it would have been quite easy to deal with it, but there was a great mix of very light gradients from so many frames, and it took me a lot of trials and analysis until I was convinced I had built a background model that would mainly subtract gradient signal and nothing else (and nothing more). Although it's quite possible that not ALL of the faint but visible data is 100% accurate, I believe most of it is. Here's some of the data and processing involved to "flatten" the master luminance data.

Below you can see the master luminance after being cropped (to remove "bad" edges due to misalignment between frames) and with nothing else done to it but a non-linear stretch tailored to reveal the gradients in the image:

And here you can see a non-linear stretch version of the final background model applied to the image:

As you can see the background model is very smooth and gradual even after a strong stretch - obviously when the background model was subtracted, it was in linear form and visually it looked like a completely dark image.

PROCESSING

The processing of the data did not include at any time any curves transformation, DDP nor selective or masked histogram stretch. All data stretching was done by unmasked and non-selective non-linear histogram adjustments.

More specifically, after the gradient removal, a rather standard process was done to the luminance/lightness data, that mainly included:

  1. Slight deconvolution, with masks at three levels: local, global and external. The purpose of the local and global masks was to avoid the Gibbs effect, and the external (lightness-based) mask was used to avoid applying deconvolution to areas low in SNR, and increase the deconvolution effect as the SNR improved.
  2. A first non-linear unmasked histogram stretch.
  3. Masked ACDNR (noise reduction). The lightness-based mask here served the opposite effect of the external mask used for the deconvolution: applying the noise reduction only on areas low in SNR and gradually reduce the effect as the SNR improved.
  4. A second non-linear unmasked histogram stretch. This is because after the noise reduction, our histogram has been altered, and so it allows for a new adjustment.
  5. Masked HDRWT. This is the process that reduced brightness in the larger galaxies and also revealed some of the data and details in them. The lightness-based mask here is also helping avoid ringing.
  6. A third non-linear unmasked histogram stretch. Again, we readjust the histogram because after the HDRWT process we have a different scenario that allows a new adjustment.
  7. Slight masked sharpening using wavelets. The lightness-based mask here kept noise from being sharpened.
  8. Very light masked morphological transform. This process reduced overall presence of the largest stars, bringing them back to their form as they were prior to the last histogram adjustments. A star-based mask is necessary with every morphological transformation process, otherwise we would be applying the morphological changes to structures that shouldn't be affected by it.
  9. A last histogram adjustment.
  10. A last masked Laplacian sharpening.

In between some of these processes, I did integrate scaled before/after images via PixelMath at some stages during the processing, to apply a process only so slightly...