Saturday, March 17, 2018

#128 - Thursday, March 15, 2018 - The Clear Skies Call, and I Must Go

With springtime due to arrive any day now, the weather goes through its usual rough transition as winter grasps each day and refuses to let go.  Cloudy days can turn into sunny days at the drop of a hat, and vice versa, so when I saw it was sunny on Thursday, I waited until the last minute to decide whether to make the trip out to the observatory or not.  The forecasts made it look like there would be occasional clouds rolling through, but nope, it was clear as a whistle the whole evening!  In fact, I saw more stars than I've seen in a while from the observatory, meaning that transparency and seeing were much better than predicted.

I got out there a little after 7 with the hopes of taking flat frames before the sun set, but alas, the sky was darkening too quickly to get flat frames that were all the same exposure time, once I figured out how to use SharpCap's flats tool.  I'll just have to deal with vignetting in my images a little while longer.  I did mark the orientation of my camera to the filter wheel, and the filter wheel to the topmost screw on the club's refractor, with a silver sharpie so that I can align my camera the same way with reference to the telescope every time, so I can keep using the same set of flat frames.

Despite the beautiful skies (or maybe because of them), knowing that luck can only extend so far, I faced a number of other challenges this evening.  After I got the camera attached and marked, I slewed to Dubhe, the star on the top outermost edge of the ladle of the Big Dipper, so focus the scope.  I had a hard time finding the right camera settings that would let me easily see the diffraction spikes from the Bahtinov mask focusing aid (see my little blurb on this here), so I switched to the FWHM focusing mode in SharpCap (SharpCap has some really helpful focusing tools, by the way!) and used that to achieve focus by minimizing the size of the star.  This took a while, especially because even though I finally bought a USB 3.0 extension cable to connect my USB hub to my tablet, which now means I have USB 3.0 all the way through from my camera to the computer, I was still only getting less than a frame per second viewing speed.  I'll have to work on figuring that one out.

My next blockade came with calibrating guiding.  I slewed over to Regulus to calibrate PHD, since it says it will have the least amount of guiding errors if you calibrate on a star between -20 degrees and +20 degrees in declination, and I had such trouble guiding on my last trip.  I had it auto-select a bright star in the region (I slewed a little away from Regulus so that it wouldn't swamp the sensor), and it started calibrating.  But the star didn't move!  Calibration involves PHD moving the mount west, east, north, and south by different amounts to see how the star moves so that it knows how much and in which direction to pulse the mount so get the guide star back into place while it's guiding.  (See this post for more on guiding).  So you will normally see the star move during the calibration process.  I turned on my imaging camera to 30s exposures, and yes, the mount was indeed moving!  So I put the cover over the guide scope, aaaaand what I thought were stars were actually hot pixels!  Usually they're a little easier to differentiate from the stars.  I didn't have a set of dark frames loaded into PHD for my guide camera because I've had issues with it doing the dark subtraction wrong and the image turning out all gray, but I went ahead and took another set of dark frames anyway.  About halfway through that process, I accidentally hit the spacebar on my tablet, which hit the "stop" button and cancelled the whole thing!  So I had to start over...It worked this time, and all but one of the hot pixels disappeared.  So I calibrated (which went very quickly since I was looking so far south), and then slewed back over to M81 & M82, my target for the evening.  My plan was to get the rest of the RGB data I didn't get to collect last Saturday.

I set SharpCap to take repeating exposures so I could center M81 & M82 the way I wanted, but I couldn't see them at all, so I turned up the gain all the way and did 30s exposures to center them.  This took forever.  Finally I got them where I wanted them.  (I really need to learn how to use AstroTortilla, a plate-solving program where you tell it where you want the FOV, and it uses star patterns in the image with shorter exposures to center your telescope!)  I started acquiring the red images and waited for the first one to come in so I could see how it looked.  Well, it looked out of focus - there's always the risk of something moving ever so slightly when you slew the telescope a fair distance across the sky.
Out-of-focus red frame

In-focus red frame

So I took a screenshot of the coordinates where I had the scope set to (I control it from the computer - way easier than moving through menus on the hand controller!) and slewed to Dubhe to go through the whole rigmarole I went through earlier in the evening to focus.  Finally, I slewed back to the coordinates I had saved, which got me close but not exact, so I had to adjust it a little.  But this time, I used Sequence Generator Pro's Frame & Focus routine, and SGP has a tick box called "stretch the histogram," which will stretch the histogram of the preview image on the screen so that you can actually see things.  This let me take only 4s exposures, so centering the image went waaaaay faster.  Remind me to do it in SGP from now on. Finally, an hour and a half after I got started, I was ready to image.

I acquired 7 more red frames (since I had gotten 8 last Saturday and I wanted 15 total for each channel), and when I got back to swap filters, I realized that I didn't move the dome enough earlier, and part of the scope's view was cut off.  So I lost a few red frames and had to re-take them.  But it turns out I lost more than I thought, so I only wound up with three red frames.

The dome cut off part of the scope's field-of-view - notice the diffraction spikes around the brighter stars.

After that, I changed to the green filter, and those went off without a hitch.  But after the greens were done, it was time to do a meridian flip, since M81 & M82 had crossed the meridian that divides east and west.  Equatorial mounts have to flip around for each part of the sky in order to keep the telescope from hitting the mount.  Doing this always means adding a lot of extra time - usually I have to re-focus again afterwards, and it doesn't always go back to the exact same spot in the sky, so I had to re-center the targets again.  But first, I had to deal with another problem: the guide camera fell out of the guidescope while the mount was flipping around.  This meant that I had to re-calibrate, since it would be impossible to get it back into the exact same orientation it was when I calibrated earlier.  I didn't want to slew all the way back over to somewhere south, so I just calibrated where I was at.  It worked just fine.  In fact, the seeing was good enough that guiding was more accurate than usual - I could see the pattern of the periodic error in the mount, and I was getting nearly only 1 arcsec of error, which is great for this area.

Not the best guide graph there ever was, but not bad...and good enough for how large the FOV of my camera + telescope combination is (1.3x1 degrees)

The blue frames went off without a hitch, and then I finally got to pack up and go home around 1:15 AM (I had only planned to stay until midnight, but I reaaaallllyyy wanted to get the rest of the frames I needed to make a complete image).  I got to sleep around 2 AM, and still had to go to work the next morning!  I didn't feel all that tired on Friday, but I had a very difficult time typing, either on my phone or my computer - I kept making lots of mistakes.  But I powered through!

I've gotten good at stacking LRGB images in DeepSkyStacker (post on that coming soon), but post-processing in Photoshop proved to be a challenge.  Color balance was difficult.  But the synthetic flats procedure I recently learned worked really well (post on that soon too).  I'll eventually write a post on the post-processing process, but here's a quick rundown:

These are the raw FITS files for each color channel.  They look blown out, but they're not - the FITS viewer I use (AvisFV) stretches the histogram a bunch, or else you wouldn't really be able to see them.  Blue is reversed from the others because I had to do a meridian flip.

After stacking in DeepSkyStacker, saved as 32-bit, and imported into Photoshop.  Notice that DSS aligns them (I'll explain how to do this in a future post)

Stretched & flattened with synthetic flats

RGB images combined in Photoshop

Luminance image applied as Luminosity layer

And...drum roll please...after additional work in Photoshop...
Date: 10 & 15 March 2018
Object: M81 & M82
Camera: ZWO ASI1600MM Pro
Telescope: Vixen 140mm neo-achromat
Accessories: Astronomik LRGB Type 2c 1.25" filters
Mount: Losmandy Gemini II
Guide scope: Celestron 102mm
Guide camera: QHY5
Subframes: L: 18x180s
   R: 11x180s
   G: 18x180s
   B: 14x180s
   Total time: 3h3m
Gain/ISO: Unity (139)
Stacking program: DeepSkyStacker
Stacking method (lights): Auto-Adaptive Weighted Average (x5)
Darks: 20
Biases: 20
Flats: 0
Temperature: -30C (chip), 29F & 35F (ambient)

I still didn't manage to get the red hydrogen gas being ejected from M82, but hopefully someday...I'll need to take much longer exposures.  Or use a hydrogen-alpha filter :)

Pretty excited about this camera and my increasing skill level!!

Sunday, March 11, 2018

#127 - Saturday, March 10th, 2018 - Daylight Saving Time, and Other Tales of Woe

The forecast coming up on Saturday night was uncertain - cloudy, clear, clouds at 6 PM gone by 8 PM, clear until 11 PM and then clouds...none of the forecasts agreed, and when that happens, there's sure to be at least a few thin clouds floating around.  There were, but they mostly stayed toward the horizon, so a dedicated few of us from the club layered up to brave the cold and do some astronomy, as well as prepping for next Saturday's Messier Marathon.  (The Messier Marathon is a clear night in mid-to-late March when a dedicated observer can power through all 110 Messier objects in a single glorious night).

Due to getting sidetracked spending the whole afternoon tearing my house apart in search of my Raspberry Pi 2 that I need for a workshop I'm attending this week, I didn't leave the house until sunset, so it was dark by the time I finished setting up.  I had hoped to go out early so I could take some much-needed flat frames (see this post about what those are good for), but I forgot my silver sharpie to make index markings of where I took them anyway.  (All of your gear needs to be the same orientation every time if you want to use the same flats).  I need to get like a LED tracing tablet or something.

I spent the drive out to the observatory contemplating what target I wanted to shoot, and I finally settled on the Cone Nebula, which I have not yet imaged.  It was a risky decision, since I wasn't sure how well it was going to show up or how exactly to orient the image, since the view I see in SkySafari (the astronomy app I use to know where things are) can't tell me which way my camera is oriented with respect to the object.  It was also already across the meridian, meaning it was headed quickly towards the most light-polluted area of sky to the west of the observatory.  But I figured I'd give it a shot anyway.

After spending a while making sure I had good focus and then getting it centered exactly how I wanted it, I was finally ready to start imaging.  I had to take 1-minute-long subframes in order to see it, so centering the image took a while.  (And even then, I had to blow out the image just so I could kind of see the Cone).  I calibrated guiding, started the run for 5-minute exposures, and went inside.

Well, before I went inside, I took a few peeks through the club's 20-inch Dobsonian that the other club members present had pulled out - we looked at M51 Whirlpool Galaxy, M65 & M66 (part of the Leo Triplet), and M42 Orion Nebula, and they looked at a few other things while I was setting up.  M51 showed the two cores quite nicely, and if you used your imagination you could just see the spirals.  M65 & M66 had fuzzy shape to them and looked nice together.  M42 had its usual greenish cast, with the Trapezium nicely resolved in the center, with the giant curved dust lane of M43 just visible against the star that lights up that region.

I came back out 30 minutes and a cup of hot cocoa from the Keurig later to find that guiding was a mess - all of my images had some motion in them.  I stopped and re-started guiding, but was still having troubles, so I finally gave up and decided to image M81 & M82 instead, a photogenic pair of bright galaxies up north in Ursa Major.  After taking much care to get them centered exactly where I wanted them, I went to re-calibrate guiding, and PHD gave me a warning about attempting to calibrate north of +20 degrees declination, since when you're pointed north using an equatorial mount, there is not much motion in the declination axis, which can cause problems with calibration.  But I had already spent so much time centering the image that I went ahead and calibrated anyway.  It worked all right.  I took 20x3-minute subframes in luminance, and then 8 in red (I didn't want to be up too late), and then I started 8 in green and went inside, but when I came back out, the mount was hitting the pier!  The Losmandy Gemini mount that the club's memorial telescope has can go quite a ways past the meridian, so I was hoping to finish before it hit a hard stop, but that didn't work out.  So I did the meridian flip, re-centered the image, had to rotate the camera since it had gotten bumped, re-focused as a result of that, and then finally re-started the green frames, only to have guiding not work (you can flip the calibration without having to re-calibrate).  It was weird - the graph that shows the corrections that PHD is sending to the mount was totally flat, which would normally indicate that maybe the image coming from the guide camera wasn't actually updating, but when I bumped the mount, it sent a correction command (albeit a tiny one).  But I had previously been getting upwards of 1.5 arcsecs of RMS error, a measure of how much PHD was having to correct the mount, and there was no way it was even possible to be flat like that(it would have require perfect atmosphere conditions and no mount tracking errors).  At that point, it was already nearly 1:30 AM, and I had to get up and go to church the next morning, especially since it was Girl Scout Sunday and two of the girls in my troop were receiving a religion award they had earned.  So I packed everything up and headed for home.

To add to this underwhelming night, I left the observatory at 1:45 AM and got home at 3:15 AM - thank you Daylight Saving Time!  Ugh.  I only got 4 hours of sleep, and that was with skipping a shower.  I may or may not have drank coffee during Mass...

If nothing else, I did get a usable stack of L images, although I don't have flat frames for them.  I cropped the image to remove at least some of the vignetting.  It looks promising, though.
Date: 10 March 2018
Object: M81 & M82
Camera: ZWO ASI1600MM Pro
Telescope: Vixen 140mm neo-achromat
Accessories: Astronomik LRGB Type 2c 1.25" filters
Mount: Losmandy Gemini II
Guide scope: Celestron 102mm
Guide camera: QHY5
Subframes: 18x180s (54m), L only
Stacking program: DeepSkyStacker
Stacking method (lights): Auto-adaptive weighted average, x5
Darks: 20
Biases: 21
Flats: 0
Temperature: -30C (chip), 29F (ambient)

Nights like this are a good reminder to all that astrophotography is hard!  There are a lot of things that have to come together in order to successfully make an image.  But if you persevere, great images will result eventually!

Sunday, March 4, 2018

#126 - Friday, March 2, 2018 - Curing Cabin Fever

It has certainly been a cold, cloudy winter this year!  I've only been out eight times since winter began, and one of those was an outreach event.  The last time I was out imaging was over a month ago, so I'm glad to be back!

And I'm especially glad because I have a new camera!!  After saving up for the past year or so, I have finally saved enough to buy the ZWO ASI1600MM Pro for $1,280 (that's the low end for astrophotography cameras!)  It arrived on Wednesday.  Now, the rule in astronomy is that once you get a cool new telescope or a fancy new camera or eyepiece or something you're really excited about, you are bound to have clouds for at least a week or two.  However, I was strategic in my timing: it has been cloudy here for the past few weeks with lots of rain, and now that it was finally cleared a bit, the moon is full.  But!  The full moon gives me a chance to go test the camera to make sure everything works and get some preliminary results on it.  I just had to choose a bright target.
The ZWO ASI1600MM Pro astrophotography camera.

So, of course, I went with the classic first-light target: the Great Nebula of Orion, Messier #42.
I'll get into the details of this camera in a separate post soon.

The weather was cold, hovering around freezing, but there was no wind, so it was tolerable with a sufficient number of layers, as well as my new snowboots paired with my thermal and wool socks.  The Asian beetles inside the memorial dome appear to not have reanimated in the recent spout of warm weather we've had, although there were a few moving flies inside.  The carpet squares on the floor were soaked from the rain, which must have leaked in from somewhere, but the electronics all seemed fine.

Setup went smoothly, thanks in part to some at-home setup - before I left, I scrambled to get the drivers updated and tested.  The ZWO English software site was down, but I managed to find the Japanese version of the software page, where I was able to locate both the latest camera driver and the ASCOM driver, which were necessary to connect this new camera model to my computer.  (I had older versions of both drivers that I had used last May at the Texas Star Party to run the ZWO guide camera I borrowed from my minion Miqaela).  Crisis averted!

My new ZWO ASI1600MM Pro attached to the Vixen 140mm refractor I borrow from my astronomy club.

The atmosphere wasn't great - I was getting around 2.8 for the FWHM of the star I was focusing my guide camera on, and the guiding was bouncing all over the place with a RMS error bigger than 2 arcescs, which lead to unstable guiding (even with 3-second exposures) that squished my stars this way and that way on all of the subframes, but being under a full moon anyway, I was less concerned with that because the main goal was to test out the camera.

I first tried the Horsehead & Flame Nebulae, but they were not bright enough to shine through the moonlit sky, even with a 5-minute exposure.  So next door to the Orion Nebula I went!  I decided to take 60-second subframes since I didn't want too much background light from the moon.  I also took a series of 5-second luminance subframes to composite with the 60s ones so show detail in the core  of the nebula, which was waaaay blown out in such a sensitive camera at 60 seconds.

60-second luminance frame, stacked (39x60s), stretched 

5-second luminance frame, stacked (45x5s), stretched

I tried a technique from this video by David Rankin to blend the two luminance frames in order to capture the dimmer areas and finer detail of the 60s image with the detail in the brightest parts of the nebula of the 5s image.  It worked quite well, and was pretty easy!

After stacking and stretching the red, green, and blue channels, I combined them into one image in Photoshop (I will eventually write a tutorial on this once I have more practice), added the composited luminance frame on top and set the layer type to Luminosity, and set to work tweaking the Levels, Curves, and Hue/Saturation to my liking.  The colors came together amazingly well - I used my new Astronomik LRGB Type 2c filters, which say they are designed to be color-balanced in sRGB space, the standard color space.  That definitely proved to be true - I had to do very little adjustment of the colors, really just reducing their presence in the background (from the moonlight and light pollution). 

All right, here it is!
Date: 2 March 2018
Object: M42 Orion Nebula
Camera: ZWO ASI1600MM Pro
Telescope: Vixen 140mm neo-achromat
Accessories: Astronomik LRGB filters
Mount: Losmandy Gemini II
Guide scope: Celestron 102mm
Guide camera: QHY5
Subframes: L: 39x60s (39m)
                                       L: 45x5s (3m45s)                   
                                    R: 26x60s (26m)                  
                                  G: 26x60s (26m)                 
                 B: 22x60s (22m)
Total time: 1h57m
Gain: 139 (unity)
Stacking program: DeepSkyStacker
Stacking method (lights): Auto-Adaptive Weighted Average (x5)
Darks: 25 (60s)        
 30 (5s)
Biases: 21
Flats: 0
Temperature: -30C (chip), 29F (ambient)

The fine details in the nebula clouds are so amazing!  No longer are they lost due to noise.  I didn't have to do any noise reduction on this image, even with the short exposures.  I feel like I can reach out and touch it!  I also saw that if I crank up the exposure a ton (which makes it look kind of terrible), I also caught a lot of the very dim background of this nebula, so maybe I'll do some much longer exposure images of it as well and composite those together to make a very high dynamic range image.  Also, the giant blue stars are a result of using an achromatic refractor-type telescope, so at some point I'll need to image this again with my apochromatic Borg to get some better-looking stars.  But anyway, despite a full moon, I am super happy with this image, and can't wait to see what else I can do with this camera!  Time to take things to the next level!