Northwest Astro

Went down to OSP this year, and it was a great experience, minus the heat and the sun which I was very unprepared for. This was also a perfect place to test out some new gear, get access to really dark skies, and let loose.

Unfortunately, I’m still recovering a bit from the amount of sun exposure I got, so I only did some quick work to get the images I captured finished up and posted. They are in the gallery.

More on the trip itself later after some rest.

Badly Processed M81

Better Processing on M81

Take a quick look at the two images to the right. One is a bad example of how to process M81. Maybe not bad for a first attempt (which it was for me), but not a great galaxy in general. It has very little in the way of features, and you really only get a vague idea of what shape and details it has. One is a better example of how to process the same target. While it is noisy, it still has much more detail visible in the galaxy. You can see the characteristic dust lanes near the core, and more detail in the spiral arms. Overall, it is a much better image.

Both images come from the exact same data. 16 exposures of 5 minutes each, aligned and stacked. In fact, they both come from the same final stacked image. So why is there such a huge difference between the two?

When processing, I’m finding out the hard way that you can’t be too heavy-handed when you do the final stretching work and post-processing. If you start doing that, then you risk losing the very detail you are trying to extract from the noise.

Don’t fall for the temptation to do curves adjustments in one or even two passes. Take time on it, and do it very gradually if you have to. And resist the temptation to ‘clean up’ the image too early. Noise reduction, darkening the sky background, and so on should be left for last once you have exposed the target. Do it too early and you will lose important faint details, or will simply wash out other details.

Now, that isn’t to say you can perform miracles with bad data. While the second image is better processed, I can only do so much due to the noise in the stacked image, and the fact that the galaxy’s data is buried in the noise. My method of collecting Darks for the DSLR seems to not really do much to combat the noise. So I’ll need to take longer exposures to also help get the signal above the noise. On top of that, the focal reducer used tended to bloat the stars and probably had an adverse affect on the galaxy as a result. Since this image was originally taken, I’ve moved to a different focal reducer which has helped there.

The upside is that with extra practice on existing data (one reason to always keep around raw data as long as possible!), I’ve gotten better at processing, and should be able to tackle M81/M82 again in the near future when the weather cooperates and make a second real attempt.

M81/M82

This is a rather late post, but I’ve finally gotten the CGE out for astrophotography. As I am a bit of a glutton for punishment, I figured I’d take this opportunity to make this my first attempt at a galaxy shot as well. So I pointed my setup at M81 and M82 and started taking some 5 minute exposures.

I wasn’t really expecting to actually get an image out of this. I really just wanted to see how good the tracking was on the CGE, and how well it would run while autoguided by PHD. The tracking seems to be holding up just fine, so I am pleased with the performance I am seeing with the CGE. With the LX200 on its fork mount, I was having frustrations keeping the guiding running well beyond 2 minutes or so, while this gave 5 minute subs no sweat.

Now, that isn’t to say there aren’t things I’ve learned this time out:

• I think the filter I used impacted the brightness, and I didn’t take long enough exposures to really get the detail I could have gotten here.
• I did figure out how to user layer masking to restore M82’s core after stretching to make M81 visible, which led to a fair amount of preserved detail there.
• Noise is probably gonna kill me if I keep shooting galaxies like this with not enough exposure. You can see a fair amount of noise creep into M81 on the right, and really if I need to take longer exposures, the DSLR I am using will start becoming the weak link. Dark frames will help less and less, and more noise will be even more visible with longer exposures, and it will be even harder to get more exposures to balance that out. And it will require even longer exposures to get the signal above the higher-level noise.

Although for now, enjoy.

Lunar Terminator

I’ve been reorganizing all the shots I’ve taken so far, and revisited the Lunar mosaic like I wanted to. With some better stitch tools, this came out absolutely fantastic. I’ve also posted a saturated version of the mosaic as an example of just how much detail of the lunar rock and dust we can actually see from down here with a modest telescope.

As a little bonus, I have managed to salvage a moon shot I took awhile back. I was originally going to use it back in the Sept DSLR bright imaging contest on Cloudy Nights, but the target was already in the lunar shadow.

Last night, the clouds broke and let me back under the stars in this light polluted suburb. I’ve been itching to use the small refractor on the Double Cluster for a couple weeks now, after I first attempted to get an image using the larger 10″ scope, and realized the two clusters together just don’t fit. Focal reducers help, but you are literally filling up the whole frame, which gives you no wiggle room when it comes to light falloff on the edge, or cropping away artifacts from stacking images together.

Draft

Processed

I managed to get roughly an hour worth of exposures with nearly perfect tracking, despite a rough alignment, and still tracking in Alt/Az. Unfortunately, I forgot to bring out the dew shield for the 10″, so after the images were taken, there wasn’t much hope for doing any visual observing with the big scope. I took my dark and bias exposures before heading in for the night.

This morning, I’ve been cobbling together the work from last night, running the data through pre-processing, and using the Drizzle stacking method for the first time in Nebulosity. I’d say the results turned out rather well after letting it grind on 85 images 12 Megapixels in size. With a DSLR, I find that you really don’t want to let Nebulosity scale your image up too much, as you already have an awful lot of pixels available.

I’ve posted two results. The first is my draft image of the Double Cluster, where most of the work after the stack was done by manually setting white balance and adjusting levels. The second is the more heavily processed version where I let Nebulosity try to filter out the skyglow for me before adjusting the levels, and I more aggressively cropped the clusters. You can more easily see fainter stars in the second, more processed image. Unlike most, I don’t like blowing out my stars to make the faint stars brighter and instead go for a more ‘faithful’ approach, and unfortunately that does have the effect of keeping the faint stars darker. Because the shot was taken at ISO 1600, it does still have a fair bit of grain in the image even after processing with a fairly sizable stack of darks. I am still learning a bit, and may revisit these particular images in the future when my post-processing skills get a bit better.

Ring Nebula

Took the scope out again last night, and decided to try imaging using my 0.5 reducer on M13 and M57. Unfortunately, I picked the wrong order, and so things were not as fruitful as I expected. I started on M57 before trying to image M13, and so M13 was entering the trees by the time I got to it. The end result is that I might as well have been imaging without the reducer at all. It was a total bust, and the colors were off, possibly from stray light off the treetops.

M57 turned out a bit better, but now I fully realize just how much light comes out of these nebula along the hydrogen emission lines. With the stock IR filter on the sensor, it blocked most of the red color, and no amount of post-processing could get it back.

This was also my first night seriously trying to use dark frames, and I think so far the dark frames have been doing what they need to do and reduce noise. Also, I realize this particular focal reducer is not what I want to be using. It exaggerates the curved field to the point where there is a very small area to image with. I should probably sell the 0.5 reducer and get a 0.63 reducer/corrector instead. Although I might keep the reducer for visual observing, as the extreme curvature isn’t as noticeable there, and the views are still rather impressive.

It seems like a rite of passage, as nearly everyone’s first deep sky image is of the Great Cluster in Hercules. It is bright, and you can take good images in under 30 seconds so you don’t need to put a wedge on your tripod to take the picture. At least as long as your stacking software can handle rotation + translation between images.

Half-Moon

Before we went out front to do any observing though, I managed to get a few shots in RAW of the half-moon. One of them turned out to be pretty good. 1/200 second exposure at ISO 100 with the focal reducer. Having a hard time getting focus and I am starting to suspect the focal reducer might be involved.

So after we got the scope set up out front, I showed him a few objects, like Jupiter, M13, M57, the usual starters in the summer sky. Unfortunately the level of light pollution makes visual observing of galaxies fairly difficult. Later on we were looking at the Double Cluster in the f/5 focal reducer and noticing how one cluster looks pretty average, while the other has 3 bright red stars in it. He commented “You should photograph this.”

Draft

Processed

So, I hooked up the DSLR to the scope for deep sky for the first time and tried taking shots of the Double Cluster with the focal reducer in place. Everything seemed curved and stars ‘blown out’ (loops of unfocused light flaring out from the star). Removing the focal reducer, I pointed it at M13 instead and took 50 exposures over about 30-40 minutes. The best 13 frames make the two images you see below.

The one on the left is a little unprocessed, and you can easily make out the skyglow from the moon and light pollution. The one on the right has been processed to try to darken the background as best as possible without using a mask, as well as try to bring out some of the color differences in the stars. M13 is a mix of yellow and blue stars, and I wanted to make that obvious to someone looking at the image.