What I Don't Know About Image Processing...

... can fill a warehouse.

I revisited my earlier M42, M3 and M51 image sets to give them another go around in software.

As it turns out, there's a lot more detail in there which I simply don't know how to extract.

These images are the results of my experiments.  I included both the old and new for comparison.

M42

First pass

Second pass

M3

First pass

Second pass

M51

First pass

Second pass

For each of them, more noise is apparent.  This isn't surprising giving how the image data is being stretched.  These image sets have bias frames applied against them, but no flat frames.

In each of them, I had to brush out dust mote imprints and subtract vignetting in Photoshop as a postprocessing step.  I'd like to try minimize this by pre-processing the raw frames with flat field images. I haven't taken any of those yet.

The two biggest changes I made in processing these images was to:

1. Not overdo the levels stretching.  Watch that histogram closely.  It's more important to get a nice bell-ish curve going (depending on the image) than to try make your background deep and your stars pop. The moment any "blackening" or "popping" occurs, you've probably lost data.
2. Curves!!!  Holy smokes, this made a big difference!  Being able to recognize what you want to draw out, and then manipulate the curves to reflect it, has had the biggest impact.  The same rules with stretching the levels applies.  Avoid any clipping (if reasonable) so cores aren't blown out and faint stars aren't lost.

M3 and M51 with some new equipment!

Tonight was the first night I got to actually use my new Canon 1100D/T3 and SSAG!

The night before was filled with trial and error as I practiced setting up the C6-N with the new equipment.  I had to figure out issues like balance and alignment with and without the camera and autoguider. These two gadgets added about three or four pounds to the mount which really needs consideration.

I also had new software options to figure out now that my new camera is actually well supported by Nebulosity!

Here's what I learned during the prior evening of tribulation:

(Please comment if you know of better/alternate ways.)

Balancing

This started out as a point of confusion for me.  I didn't want to balance the scope without the camera and autoguider, but I also didn't want to align the mount/scope with the camera and autoguider.  I figured I had to try compensate for the weight difference between the two so I could balance and align the scope as though the camera and autoguider were attached.

Luckily, my autoguider's guidescope is the same 9x50 finderscope as the one used on my Orion XT10i.  The difference between the two scopes is that one has the autoguider hanging off the end while the other has the correct-image right-angle eyepiece thing.  So, instead of using the C6-N's lightweight 6x30 finderscope to balance and align with, I used the finderscope from the my XT10i.  The weight's weren't exact, but they were close (enough?).

As a side note for the C6, I generally find that the straight-through 6x30 finderscope is much easier to use than the "correct image" right-angle finderscope.  Being able to use both eyes to direct a star into the middle of the cross hairs makes things go much faster, especially if it's later in the evening and there are more stars out (making it more difficult to distinguish between the alignment star and the others).  For that matter, I found my Meade ETX125's reflex/red dot finderscope to be the easiest of them all.  The first time I took my XT10i out to the relatively dark skies of the Catskills in New York, I had a really difficult time aligning the scope.  I couldn't tell the alignment star from all the rest that suddenly appeared in the finderscope.  From suburban Philly I'd never had that problem before.  (My green laser pointer really helped me here).

I then looked at how to match the DSLR's weight in the eye piece.  My heaviest eyepiece, a 1.25" 32MM isn't the greatest to use during alignment, and I preferred to use my 20mm illuminated centering eyepiece from Orion (ICE).  Neither of them matched the weight of the camera.  So, I rigged a crude weighty necklace made from washers and zip ties to drap around the ICE to bring it up to scale.

I balanced the scope on the CG-5, and was good to go!

Alignment

After I managed to balance the scope as though it had the imaging equipment on it, alignment was pretty ordinary except I spent a bit more time doing the All-Star Polar Align routine.  Autoguider or not, a bad polar alignment will give you drift/field rotation in your exposures.

I'd still like to pick up a polar axis finderscope to see how well the polar alignment routine works with the CG-5 (or to make it easier), but it seems to work pretty darn well!  Turning the azimuth knobs gets difficult, though, the further you have to push the mount over.

I still find it fascinating to watch the mount get progressively more accurate during the addition of calibration stars.  By the time I get to the third or fourth star it, more often than not, gets dumped virtually in the center of ICE.

When I eventually switch out the eyepiece and finderscope for the camera and autoguider, it's nice to know I won't have to hunt for the target.

Software Test Run

After I had spent roughly 3 hours getting all this done, I eventually got to sit down with Nebulosity and the camera.  I was looking forward to trying Nebulosity's frame and focusing routines.  Apart from learning the various quirks of the software and it's interface, it's all relatively straight forward.  I did discover the following points though:

• Live view on the DSLR (pulled into Nebulosity) is very useful for framing.  Not as much for focusing.  I think I should give this another try though.  I take a ton of frames during this procedure, and maybe live view would help extend the mechanical life of the flip mirror enough that I should be using it more.
• Nebulosity's fine focus routine is where the live view shines.  The instant feedback is tremendous.  However, I still use my bahtinov mask during this process.  I've come to heavily rely on observing the diffraction spikes and it hasn't failed me (yet).

After I had framed and focused on my target DSO, I engaged PHD.  Sadly, my 10 year old Celeron-based Compaq Presario's battery threw in the towel.  A few seconds after PHD started calibrating, everything went dark.  Frustrating, but not entirely unexpected.  I wasted a LOT of time figuring out the issues, and the Compaq's battery only lasts about 2 hours.

The Imaging Session

Tonight, the set up went much better thanks to my experiences from the previous night.  At the same time, I used my mid-2009 Macbook instead of the 10 year old Compaq.  After 3.5 hours of imaging with it, it still had 60% battery left.  Plus it's a vastly more capable machine, power-wise.  It didn't stutter or stall at any time during the evening.

My first target of the evening was M3.  I started with ten 25 second exposures at 800 ISO just to get the hang of the camera control in Nebulosity with the guiding of PHD.

The seeing was apparently not great as PHD would occasionally warn me that the guide star's mass had changed.  Luckily, it always appeared to stabilize a second or so later and PHD never actually lost its lock on the star.

The one thing I learned from this?  Make sure you take off the bahtinov mask before you start imaging.

Next time, I'd like to try image M3 with a greater exposure time to try resolve more of those stars.

Messier 3 (Globular cluster in the north constellation of Canes Venatici)

My second target was M81 and M82 together.  For some reason, PHD had a lot of trouble with the telescope in this orientation.  It was unable to detect movement in the right ascension.  Switching the guide star didn't help at all.

I gave up on Bode and the Cigar after taking a few unguided 2 minute exposures.  I didn't want to waste my time taking shots that would probably be unusable anyway.

I then shifted downwards to M51, the Whirlpool galaxy.  After framing it through Neb, and re-calibrating PHD, I started a run of 10 exposures at 5 minutes each at ISO 800.

Messier 51 (Whirlpool galaxy in the northern constellation of Canes Venatici)

A few learned facts from this set:

• Doggone skyglow.  I've gotta get me one of these clip filters.  I've heard good things about them, and heck, it's my only real option with this equipment.
• Take more exposures than you think.  I lost half of my ten subs from a surprise breeze, satellites, a plane and a late night visit from from a neighborhood dog.
• Bring something else to occupy your time during a long shoot.  Apart from occasionally glancing at PHD to make sure everything is going okay, there's not much to do.

I decided to also try image M101 (Pinwheel galaxy), but it wound up being rushed and just a waste of time.  And overall, the biggest thing I learned:

• Choose one, maybe two, targets to image in a given night.  Bias frames are fast and easy to take, but if you want to also shoot flats, that'll add a great deal more time to the process.

The Orion Nebula - Redux

If a particular DSO can be considered a cliché, M42 is probably it.... but, frankly, I wait all year for The Great Nebula in Orion to appear in my skies.    It can be seen with the naked eye, it's a staggering sight in any telescope of reasonable aperture, and it's an easy target for imaging!

It's a pity it only appears (high enough) in mid-winter.

I couldn't let this winter go by without taking a picture of it with my C6-NGT.  My last shots of Orion were with my Meade ETX 125.  While they weren't horrific, they also weren't great.

Suffice to say, my first attempt at imaging M42 with my C6-NGT went vastly better.  I wouldn't classify this image as "fabulous" (not by a long shot), but for a beginner I would certainly call it "great".

Messier 42 (NGC 1976) - The Great Nebula in Orion

There's a lot wrong with this image, from the ever-present coma, to the overexposed and blasted out trapezium and the lack of whispy volume as the nebula fans out across space.

However, I'm also getting more comfortable with my hardware and software.  Nebulosity by Stark Labs along with tutorials and guidance from sources like the Astronomy Shed on YouTube, the Astronomy Forum and Cloudy Nights has been invaluable.  I learn something new every time I take a picture.

This outing has convinced me that an autoguider would be a very useful addition to my toolkit.  So,  I've picked up the Magnificent Mini Autoguider package from Orion Telescopes and Binoculars.  The included guide scope should work well with the newt, but my mak's 1900mm focal length is likely too much.

Messier 32, not 31 (or is it the other way around?)

I have hard time remembering which is the Andromeda Galaxy and which is the smaller companion gallery.  So tonight I decided to image M32, what I thought was the big one.  Which it isn't.

Luckily, M31 is so honkin' big that it clearly fit in the frame anyway (and then some).

This image of M31/32 was created from 4 subs at 60 seconds each, with the camera's ISO set to 1600... and it's definitely not enough exposure time to bring out the whispy arms of this galaxy.  Oh, the arms of the galaxy are there.  If I dramatically overexpose/level/curve the image, the "lower" arm wrapping around the right edge of the core is easily visible.

Messier 31 and 32 (NGC 224) - Andromeda galaxy in Andromea

This image makes me want to get an autoguider even more so I can more reliably track these guys for longer periods of time.  Despite the lack of definition in this image, it's still tremendously exciting to see massive, faint, far flung objects appearing in front of your eyes.

The Bow Tie Nebula

To finish off this weekend I tried to photograph something I hadn't looked at before.  What I learned about Caldwell 2 is that I'll probably want to barlow it when using the newt, or try capture it with my Maksutov instead.

The nebula was tiny.  Also, since the DSLR has a (relatively) large sensor compared to some dedicated entry-level CCDs, the DSO was even smaller in the result. At first, using the LCD display of the DSLR, I thought my subs weren't capturing anything but some colorful noise in the center of the images.  However, the noise was a little too consistent and large.

C2 (NGC 40) - The Bow Tie Nebula in Cepheus

One thing I've come to appreciate with the CG-5 is how consistently it pinpoints and centers the target in the eyepiece.  Chalk it up to good mechanics and/or a great alignment, but it sure helps the night go more smoothly!

I've really started noticing now how much coma is in some of these images around the edges.  Although I'm able to crop out some of the vignetting and coma, I'm beginning to understand why a field flattener or coma corrector is needed with these faster scopes.  Maybe this is also why people enjoy imaging with catadioptric scopes, too.  The higher focal length helps reduce some of the coma.

The Mak and the CG-5

Since getting the Meade ETX 125, I'd wanted to try take photos of the sky using it.  When I got the C6-NGT, I suddenly had a good mount to try it!

Since the ETX 125 OTA already has a mounting block with dual 1/4-20 holes in it, I just had to find an adapter to marry the scope to the CG-5.  Luckily, ScopeStuff sells just the thing!

Given how much slower the Meade mak (f/15) is to the Celestron newt (f/5), it's not a surprise that the images produced by the mak were much "dimmer".  All things equal, from the camera's perspective (exposure length, ISO), the C6 produced much brighter images.

What I don't recall, and what will necessitate another trip out with the mak, is how much coma was present.

My first shot with the mak and CG-5 was Albireo:

Albireo - Double star in Cygnus

I don't have a good grip on photographing stars yet.

My second shot was a single frame of M57:

Messier 57 - Planetary nebula in Lyra

As an experiment, I decided to do a comparison between a 30 second exposure and a 60 second exposure with all other things being equal:

Messier 57 - Planetary nebula in Lyra

Once I get an autoguider, I'd like to try thing experiment again, bumping up the exposure time incrementally to see how things are affected.

The C6-NGT and Astrophotography Take 2

On this night I decided to try image two targets.  One that I could clearly see with the telescope and another that I couldn't.

This round, two things were different:

1. I spent the time ensuring I had a better alignment.  It took a great deal longer, but the results blew away my first shoddy attempts at taking pictures with this gear.  Instead of doing a simple two-star alignment with an additional calibration star, I did a two-star with several calibration stars AND I performed Celestron's All-Star Polar Alignment routine.
   
   Assuming the All-Star routine really works (which is evidently does), it's really amazing how far off my mount was in pointing to the north celestial pole.  I don't have a polar axis scope, and given other amateur astronomers feedback on the All-Star routine it looks like I may not really need it!
   
   On a good night, the alignment routine will take me 15 minutes.  This is a far cry from the 45min+ needed for a good drift alignment.  I also assume it's not as accurate as a carefully applied drift alignment.  Regardless, the All-Star routine gave me one minute exposures with virtually no trailing.  Maybe I was just lucky!
2. I bought a bahtinov mask from Farpoint Astro.  This took all the guesswork out of focusing and as far as I'm concerned, is a cheap no-brainer accessory to add to your imaging toolkit.  I couldn't imagine focusing without it.  I first tried to make my own, but I eventually decided that $18 bought me a piece of equipment vastly superior to what I could make.

The Easy Target

M92, a globular cluster in Hercules is nice and bright in the eyepiece.  You can easily see it in a short exposure and is therefore easy to locate and center.  You don't have to spend hours imaging and processing to discover that your target is being clipped accidentally.

M92 - Globular cluster in Hercules.  4 x 30"

The alignment is definitely better, with little to no trailing.  However, evidence of coma clearly shows around the edges of the image.  Darn newt.  Well, maybe when I get better at this I can look into a coma corrector.

The Hard Target (for me)

Caldwell 34 -- the Veil Nebula in Cygnus -- is a DSO I can't see from my home with my telescopes, although I have seen it in my 10" newt at a dark(er) site.

I only took one sub of the Western Veil (30 seconds at ISO800) and at first glance I could see nothing...

C34 - Veil Nebula in Cygnus

... but it's there!  This was my first face-to-face with a DSO that would need more subs, a longer exposure and heavier processing to draw out the details.

Here's a Photoshopped version of the same image to help draw out the nebula: