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.

I’ve only had a couple clear days in the past month and have found that I still have quite a bit to figure out about shooting from urban skies. I’ve been attempting M81 again, only to find out that I am just not getting enough subs to bring out the detail from the noise that I want.

Looks like my next attempt will be M13 again. While I plan to do a multi-night shoot on a harder target.

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.

So, a couple days after getting the shot of M81 and M82, I took the scope out again to experiment with shooting M81 by itself through the LX200. Although I made a couple mistakes. First, I shot on the day after full moon, and second, I ran shorter exposures on the LX200 than I did with the Orion and the widefield shot. Some napkin math tells me I should have upped the exposures to 9 minutes from 5, but I was trying 2 minute exposures instead. So the end result is that I got pretty much nothing for my hour of exposure time.

But, determined to not let the clear night go to waste, I turned the scope to the moon, and tried out a polarizing filter I picked up awhile back. I knew a lot of people swore by these things, but I didn’t quite expect what I was able to see. I saw quite clearly, all the gradients in the surface of the moon. The sort of things you can usually only make out on a super-saturated photograph. I thought I saw color, but at the same time, it could have been false color introduced by the filter. I’ll have to try it again to know for sure.

I also noticed Saturn was up for the first time since I got the LX200, so I pointed the scope at it as well. With the ETX-125 that I had previously, I only ever saw Titan next to Saturn when I was at home. At a dark site, I was able to pick up a second moon (never knew which one). The first thing that jumped out to me was that I could see 5 moons. My collimation was off, but I could make out the gap between the rings and the planet, and 4-5 different bands across the planet itself. More detail than I had ever seen of the planet to date. I’ll definitely have to revisit Saturn later and try some planetary imaging again.

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.

M42 Capture

I have been having trouble getting guiding to cooperate during the last couple nights out when the skies have been clear, and have been trying to reduce various sources of vibration and other error (that I have control over, anyways).

This weekend was actually pretty clear, and so the scope came out. I finally decided to try training the PEC on my mount for the first time. I used PHD Guiding through the LX200 to train the PEC on one of the stars in Orion. After training, I turned the scope to M42, imaging through the LX200 at f/6.3, and guiding using the Orion 80ED refractor at f/7.5. Guiding has definitely improved, and I am seeing a lot fewer ‘jumps’ in the guide star. Haven’t even bothered to try to measure the periodic error yet.

Above is a single 5-minute exposure at ISO 800 taken through the LX200R, showing the full DSLR frame. Stars still aren’t quite round, but they are worlds better than the last time I tried to take 5-minute exposures (they were previously long streaks, even when guiding with the SCT, and imaging with the refractor). Getting the periodic error down a bit has made it easier on the guiding, and I don’t see large adjustment spikes anymore.

For anyone else who is just starting out and having problems getting their exposures to last a bit longer: make sure you have trained your PEC, if your mount supports it. Even though training with an autoguider isn’t perfect, it is hands-free, and does help in a big way versus an untrained mount.

When pairing up two cameras for astrophotography, I’ve run into issues where the cameras and scopes are mismatched in such a way that autoguiding software, even with an automatic calibration tool can’t quite configure it so that you get good guiding. Instead you get all sorts of streaking introduced by the autoguider compensating in ways it doesn’t need to.

Almost all of it comes down to really just trying to make sure the light coming into the imaging camera doesn’t move a whole lot. The first step is to figure out the image scale for each camera. The formula for calculating that is:

Arcseconds/Pixel = (206.265 / (focal length in mm) ) * (pixel size in microns)

In the case of a Canon Rebel XSi that I use, the pixels are 5.2 microns in size (µm). The guide camera I am using has pixels that are 4.65 microns. I use a 10″ LX200 and an Orion 80ED. Say I am running the LX200 at f/8 and the Orion 80ED at its native focal length as a guide scope.

In this case, the XSi is running at 0.53 arcseconds/pixel, and the guide camera is running at 1.59 arcseconds/pixel. This isn’t too bad, as we aren’t capturing beyond the resolution limit of the LX200, nor the Orion 80ED, but we are really close in both cases. We do have one problem though. One pixel of movement in the guide star is equivalent to 3 pixels of movement in the imaging camera (as a ratio of one to the other).

It gets worse too, seeing will affect the size of our guide stars, and will make the centroid of the star appear to move a little bit. For us to image at this focal length well, we pretty much have to be guiding at 1/3rd of a pixel. That isn’t possible, but attempting to use settings that would adjust at these subpixel ranges will likely cause us to overcorrect too much (as a result of seeing, 1/3rd of a pixel is still within the realm of a good subpixel guide program, in perfect seeing conditions). 

So right off the bat, we know that we will likely be unable to guide at subpixel levels with this pairing very often, and will need to lower the sensitivity of the autoguiding software to get better results on average nights. And in fact this is exactly what I encountered the first time I tried to guide with this setup. The guide software kept trying to overcorrect and lead to exposures I couldn’t use. After I turned down the sensitivity, I was getting much better guiding, but still subject to some flexture (likely from the wedge and the 80 lbs of weight bolted to it). Although I will need some more nights before I can nail down exactly how much flexture I actually have.

The clouds haven’t been cooperating for the majority of the winter this year. Unusually strong winter conditions have kept clouds sitting over the Seattle area for the last few months.

What few nights have been clear enough, I’ve run into some issues trying to autoguide with the LX200. I picked up a camera aimed at being a planetary camera awhile back, and it throws most of my settings for guiding out of whack. It has also taught me quite a bit about some of the math behind getting good guiding with two cameras. I’ll have to make a quick post behind some of these new things I have learned.

Some may notice that the header for this blog now has a couple new links.

The traffic being generated has actually been growing, and I have managed to hit spikes in the range of 3GB/day and more in traffic. It means I have to take extra steps to keep the site accessible, and help pay for the bandwidth being used. I have a couple options at my disposal for offsetting the cost:

• Place up ads such as Google Ad Sense.
• Ask for donations directly.
• Offer something up for sale where the revenue can be used to help pay for hosting.

Personally, I love the look of a clean website that doesn’t need advertising. Especially when some of the ads I would pick up wouldn’t be the best or even useful for the target audience. I’d also have no control over what they are, so I couldn’t exactly block ads from a company whom I’d rather not do business with or give traffic to. Or bump up vendors who do a good job serving the customer.

Asking for donations also tends to make me squirm a little. I understand that other sites get by fine on it, and I don’t even have a problem with being charitable (there are a couple sites I do donate to in order to keep the author doing what he/she is already doing). I just don’t like the idea of asking for handouts. I really don’t. I’d rather that someone get something for their trouble.

Sample: Lunar Print

But, one option came to mind: make some of my best images available as prints, suitable to be framed or posted somewhere. After investigating my options, getting samples, re-cropping/exporting/tweaking images, and generally doing a fair amount of work, I am ready to get started. I’ve gone through a couple different online print services, and found one which I think I am happy with, on both the quality of the print and the price of it. Each size print offered is created from the original, full-size, post-processed image and re-scaled and re-cropped for each size print. You can see a sample of the highly-saturated Lunar mosaic to the right. The sample is for an 11×14 print. Larger prints will actually have smaller fonts to account for the larger area, and text will only be on astrophotographs to give a quick idea of the subject.

A couple things to keep in mind:

• These are printed on demand and shipped straight to you from the printer. They will take a couple days to print, and standard shipping will also take awhile. Expect it to take a little over a week to reach you. I will send an e-mail letting you know when the order is placed with the printer.
• Shipping to you is included in the price. International shipping is extra, however.
• Not every image will become available as a print. It doesn’t make sense to turn it into a web store when all I want is to offset the hosting costs.
• If you have questions or requests, you can reach me using the ‘Contact’ link above.

I am working on a couple articles aimed at the beginning astrophotographer, especially those wanting to learn some specific tips and tricks for capture, stacking and post-processing. So stay tuned.

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.