Saturday, August 26, 2017

A Super-Duper Primer of Astrophotography Part 10 - It Only Takes a Camera!

I suppose I should have made this one of the first posts in this series, but here it is anyway.
Plugging a camera into a telescope and getting those awesome pictures of galaxies and nebulae is fun.  But you don’t even need a telescope to get started – a DSLR and a tripod is all you need.  There is a lot you can do with just a little equipment.

Wide-Field Imaging
You can get some very nice pictures of the Milky Way with the stock lens and a tripod.  This is one I captured from outside Albuquerque, NM, on the side of the highway with a 6-inch travel tripod I threw in my carry-on backpack.


I utilized stacking here like how I do for my deep sky astroimages, using DeepSkyStacker.  Because it has a registration algorithm, there was no need to track the Milky Way.  I used a 18-55 mm lens at 18 mm.  The shorter the focal length, the less star movement you are going to have over a given period of time.  Shooting at f/3.5 with the focal length at 18mm, I can take single frames as long as 13 seconds facing southward before I start getting star trails.  I set the ISO at 3200 – ISO 6400 is too noisy for my taste, even though you will get more light.  But stacking will get you all the light, color, and detail you could want.  The above photo is 19x15s frames stacked.  I forgot to take darks, so you can see the red banding at the bottom still.  Especially from a dark site, you can get some incredible images of the Milky Way this way.  I highly recommend using a remote shutter or an intervalometer (or if your cameras has a built-in interval timer) to trigger your images so that you touching the camera doesn’t jitter the camera in the first second of the image.

There are plenty of other areas of the sky you can image this way – constellations can make for some very nice images as well.  Here is one of Orion I took this past winter.  I turned the tripod westward periodically so keep it in my sights for a longer period of time, and in DSS, you can turn on “mosaic” mode, which will stitch together all of your images in addition to stacking them.  It came out pretty neat, and you can see the Great Nebula of Orion, the Flame Nebula, and even the Horsehead Nebula if you look carefully.

 Orion Constellation, Nikon D3100, 70-300mm lens at 70mm, f/4
136x6s, ISO-3200
I have tried shooting shorter images at longer focal lengths without much success – even after stacking, they still turn out pretty dark.  Feel free to give it a try though, especially if you have a fast (low f-ratio) lens!  This is one of the few that came out decently.

Also, make sure you take these in RAW format so that stacking and post-processing go more smoothly.

Star Trails
Star trail images are actually super easy to do (although they are time-consuming to capture).  They often look like the photographer left the shutter open for hours, but this isn’t the case – if you did that, it wouldn’t be long before you completely saturate your camera chip with background light.  Instead, you take a number of shorter exposures and use software to stitch them together.  You don’t have to be in a dark area for it either, since stars are pretty bright point sources.  Choose an ISO where you are not getting too much background light pollution (maybe 800 or so – I’ve also done 1600).  Use your shortest focal length.  You can take these in JPG rather than raw.   Make sure you have your focus on manual – your camera won’t be able to auto-focus at night.  Also make sure you set your white balance on something besides Auto (I usually use Daylight), and turn off any other auto settings.  Then set your shutter speed for 30 seconds, and run your camera either on its interval timer, and intervalometer, or off a computer using something like digiCamControl or BackyardNikon/ BackyardEOS.  Take them with as short of a pause in between frames as you can.  Let it run for a few hours, probably an hour at a minimum.  After that, I use a free app conveniently called Star Trails to process them.  Basically, it adds the portion of the image with stars in it together and creates a composite image of all of your subframes, and you get those beautiful arcs.  Facing north tends to be the most interesting, since you can see the stars circling around Polaris, and you can eve see Polaris itself move, since it is not exactly above Earth’s axis of rotation, only close to it.  But you will definitely see movement in any part of the sky.  Think about your foreground when composing your image as well – having something interesting in the foreground is just as eye-catching at the star trails themselves.  After Star Trails, I’ll usually take it into Photoshop to mess with it a bit more.  Also, Star Trails has the ability to subtract out dark frames, although I haven’t tried this yet.

Here’s a quick walkthrough.
 

Open the Star Trails app, then click the Open button (picture of the folder).  Select all of your subframes.  Click Open.

Now the next step is super hard!  Just click the "Star Trails" button :D (It's the one next to the sigma symbol in the top toolbar).  It will give you a few options.

I usually choose the "Lighten-Screen-Blend" option.  The "falling stars" one is really cool too.  Then click OK.  Now just sit back, relax, and let it go!  At the end, you'll get your very nice star trail image.  Save it out, and maybe play with the color and contrast a bit in Photoshop or GIMP if you feel so inclined.


Focusing


So, how exactly do you focus on the stars when the camera can’t autofocus, and they’re too small and dim at short focal lengths for your camera to see in Live View?  I have two techniques.

Use Live View on a distant light, or sometimes Jupiter/Venus.


My Nikon D5300 will auto-adjust Live View to pick up dim objects, changing the shutter speed to as long as about half a second or so.  I’ll turn the camera toward a distant light source, like a street light or house security light or something, and then zoom in on it a ton in Live View.  Sometimes, bright objects like Jupiter, Venus, or even Vega and Sirius will show up in the Live View.  When I’ll rotate the focuser to get it to be as small as possible.  Be very careful when you move the camera after that, as those focusers can slide back pretty easily.  Some photographers have figured out ways to tape their focuser down.  I haven’t done that because I’m sure that applying the tape will move it just a tiny bit, but feel free to give it a try. 

Take short exposures.


If there isn’t a light source or a bright object, I’ll guess at the focus, take a 5-second exposure, and then zoom in a bunch on some of the stars.  When they look pixelated, that is when you are in focus.  DSLR focusers have infinity set at not quite all the way in – this is so that the autofocus doesn’t slam into the stopping point every time.  So bring it all the way in, and then slide back out just a bit to start with, and then adjust from there.  If you see little donut rings, you are farther from focus, and if you see resolved dots but not pixilation, then you are close.  This method takes longer, but your stars will be perfectly in focus.

Final Notes


When it comes to astrophotography, you are only limited by your imagination!  While my telescope rig is busy snapping away, I’ll usually run around with my other DSLR and take all kinds of images – Milky Way, star trails, Iridium flares, ISS passes, meteor showers, whatever is happening that night.  I especially love doing timelapse, particularly when looking out over an observing field full of people or with my telescope moving in the foreground.  Timelapses are especially great when there are clouds.  I’ll have a future post dedicated to that.

Friday, August 25, 2017

I won an astrophotography award!

Okay so they told me a few months ago, but I actually got the award at the Astronomical League conference in Casper while I was there for the conference and the solar eclipse.  It's the OPT/Astronomical League Imaging Award, and I got 2nd place in the Deep Sky category with my image of the Rosette Nebula!

I get a $125 gift certificate to OPT (Oceanside Photo & Telescope), and the ability to say I'm an award-winning astrophotographer!  Haha.  



They didn't have the certificate or the gift certificate there since they didn't know I was coming to the gala (I didn't know either - the email notification I got from them just said "at the AL conference," and I hadn't ordered gala tickets before they sold out, but then I saw in the program that the awards presentation was at the gala, so the organizers very kindly found me a ticket), so they're mailing them to me instead.

Yay!


Wednesday, August 23, 2017

Solar Eclipse Corona Composite

So you may have seen those awesomely epic images of solar eclipses with fantastic detail in the corona.  And you may have looked at your own images and wondered, "How do people capture that?"  I certainly did.  I knew there was some image compositing involved, and I was crossing my fingers that the exposures I took might reveal enough detail to attempt to create such an image of the sun's intricate corona.

Well, folks, image processing has again shown me its power of bringing out details in images that exist, but are hard to see at first.

As I was following the steps to create this, my sense of anticipation began to grow...and then there it was, so beautiful and wonderful!  I am simply awe-struck.
Composite of 9 exposures of the 2017 solar eclipse from Casper, WY.
Nikon D5300 on my Borg 76ED refractor.
Buy on Zazzle
Right????????

What is the corona?

Before I dive into the process, I'll take a second to talk about some science.  When I was in Casper, shortly after totality when I was showing off the images I'd captured, I had a gentleman ask me what the white cloud we were seeing around the sun was - was it the sun's light refracting through the atmosphere, or around the disk of the moon?  Now, while there were some clouds that were scattering and reflecting the light of the sun and the corona, the corona itself is essentially the outer atmosphere of the sun.  It appears to extend far from the sun, and it does - in fact, it extends far beyond the sun, and even Earth's orbit, out beyond the orbit of Pluto, to encompass the entire solar system.  The corona is a stream of charged particles coming off the surface of the sun.  It has a temperature of over 1 million degrees (Kelvin, but that high, Fahrenheit, Celsius, and Kelvin are all basically the same), which is much hotter than even the surface of the sun itself.

Normally, we can't see the corona because the sun is so much brighter that it gets lost in the glare.  NASA has a spacecraft called SOHO (Solar and Heliospheric Observatory) that studies the corona constantly.  It has an obscuration disk that blocks out the sun's light.   
SOHO satellite image, courtesy of NASA

Basically, the SOHO satellite is in its own permanent eclipse.  However, because the sun is so bright, the obscuration disk is larger than the sun - in SOHO images, you can see the size of the sun shown as the white circle.  So it is only during solar eclipses that we get to see and study the inner corona.

You might expect that the sun's outer atmosphere might be like Earth's, where it's mostly the same in every direction.  However, we can see in images and even with our eyes during total eclipses that there is structure to the glow.  This is because the sun has a strong magnetic field.  Magnetic fields have lines where it is more concentrated, which we can see in the corona.  Prominences, solar flares, and coronal mass ejections from the surface of the sun also follow these lines.  Studying the corona informs us of what's going on inside the core of the sun.

Processing Corona Images

So here is one of my exposures during totality.
Nikon D5300, Borg 76ED, 1/80s, ISO-400

You can see some lovely detail here, but only out so far.  You need longer exposure images to see the corona out further from the sun.  But with longer exposures, the inner regions become saturated, and you lose the detail there.  
Nikon D5300, Borg 76ED, 1/4s, ISO-200

Now, we had some high clouds, which is what is causing the moon to look washed out.  With shorter exposures, you can also capture details closer to the edge of the disk, such as prominences and the chromosphere.
Nikon D5300, Borg 76ED, 1/4000s, ISO-200

So you get a bunch of awesome exposures - now what?  

I don't come up with this stuff on my own.  I learned a lot of astrophotography processing by reading forums, books, and watching YouTube videos, and I've barely scratched the surface.  This process I literally just Googled and found relatively quickly, and it worked out great.  Could I tweak it more?  Heck yeah.  Most people probably spend hours on theirs.  I'll probably work on this one some more too - I didn't align them at all, and it caused a couple problems.  But I'll step through it for you here!

The Pellett Method

Let me give credit where credit is due - I followed the instructions on this page: http://www.astropix.com/html/j_digit/e_comp.html.

The first step you should do is to align your images, and then crop off the edges so they are all the same size.  When I tried to do this manually, I couldn't see the very small motions between the images, and many of the frames are too dim to see Regulus as an alignment point for de-rotating them, so I'm not sure how I'll go about doing this (I tried Photoshop's Auto-Align tool, but it didn't work).  However, mine were close enough together that it worked out anyway.  I picked out which of my images I wanted to use, put them in a separate folder, and then converted the RAW files to TIFF using Photoshop's automated image processing, and added "_orig" to their filenames so I could keep my files straight.

Next, load the original TIFFs one by one into Photoshop and apply the Radial Blur filter (Filter -> Blur -> Radial Blur), with 10 as the amount and using the spin method.  I saved each blurred image as a separate file in a folder I called "Radial Blur."  
The lovely blurry image.

Next, take the "difference" images between the original and the blurred for each image.  Open both the original and the blurred images in Photoshop (using the File -> Open dialog), and then click on the original so it's the active image you're editing.  Go to Image -> Apply Image, and select the radially blurred one (so the one not labeled "_orig"), choose "Subtract" from the drop-down menu next to "Blending, choose Opacity to be 100%, set scale to 1, and set offset to 128.  The result is a low contrast gray image where you can see the streamers.  



I think the point of the radially-blurred image is so that you can get just the detail but not color or luminosity information by taking the difference image.

Now, one at a time, add the difference images together.  Open the first difference image (the order doesn't matter, just go sequentially by filename it keep yourself straight), open the second one, then go back to the tab for the first one and go to Image -> Apply Image again.  This time, select Add as the blending type, again set the opacity to 100% and the scale to 1, and this time set the offset to -128.  Then close the second image, open the third image, go to the tab for the first image, and add the third one to it in the same way.  Do this for all of your difference images.  At the end, you'll have a composite difference image, still that low-contrast gray, but with a lot more in it now.  Save this out as well (still as a TIFF).

Look at all that awesome detail!  You can also see some dust on my telescope now, and a weird line over by Regulus that I couldn't figure out where it came from.  We'll take care of that too, in a minute.

Now, take that composite difference image, and multiply it by your longest-exposure image from your individual frames, again by going to Image -> Apply Image, and selecting Multiply this time.  

The result came out a little weird on mine, so you'll need to do some contrast enhancement, color correction, and noise reduction probably too.  Go to Camera Raw Filter (my favorite thing!), and play around with the sliders until you get something you like.  I also talk about how to do noise reduction in this post.  To remove the dust spots, there's a button on the first screen of Camera Raw Filter called Spot Removal (it's on the panel at the top of the window).  You can increase the size of the disk by hitting the ] key, decrease it with the [ key (make the size of the inner circle about the size of your dust spot), and then you just click on the dust spot and hit Enter.  It's like magic!

Once you're done here, click OK.  You will notice that the inner part of my black disk isn't black at all, but has some clouds in it, and you can see sort of the double lines of the edge of the sun where my images didn't quite line up.  Not to worry, we can cover this up.  Open up one of your shorter exposure images with a nice black disk.  Use the Quick Select tool in the left-hand panel (below the Lasso tool) to select the black circle of the moon.  Copy this onto your corona image, and it will appear as a layer.  I had to make mine a little bit bigger to fit, so go to Edit -> Transform -> Scale, and then drag the edges and corners around until it fits how you like it.  Then flatten the layers by going to Layer -> Flatten Image, save it out as a TIFF and a JPG, and you're done! 

Posting it again here because it's AWESOME.

Now you've taken your hard-won solar eclipse images, which are beautiful in and of themselves, and pulled out subtle details of each into an amazing and breathtaking composite image that captures the sun's corona like nothing else can.  Woooooot!


#106 - Monday, August 21, 2017 - Total Eclipse of the Sun

I DID IT!  I DID IT!!!!
I CAPTURED THE MOST AMAZING IMAGES!! AGHHHHHHH!!!!

So I am one of those people for whom capturing a moment on camera is of equal importance to actually seeing it.  The eclipse was jaw-dropping, heart-thumping, and incredible, but the moment at sticks out most clearly in my mind from the entire event was hitting the "review" button on my camera and seeing the images that I had captured.  An indescribable joy overtook me, and I could barely contain my excitement at how perfect they were.  All of the dreaming, scheming, script-writing, practice rounds, and hair-pulling in the months prior all paid off in that single moment when I saw the result of my labor.  But let me start first that morning so I can describe to you how it all went down!

My compatriot Sarah and I woke up at 6 AM and quickly finished packing our bags, checked out of the hotel, and grabbed a quick bite from the hotel continental breakfast.  We swung by Starbucks because I have a great need for coffee, but the line was very long, so we went to a grocery store instead and I just grabbed a bottle of coffee from the refrigerated drinks section.  We hurried over to one of the ASTROCON observing locations - the Summit Medical Center in Casper, WY.  It was only a few miles from the hotel, and there was not much traffic, thank goodness.  The Summit Medical Center was most gracious for letting us use their space - they let us come in to use the bathrooms and fill up on water and coffee, they turned off the sprinklers and the parking lot lights, brought out trash cans, had a security guard on site, and they covered the exterior lights of the building with surgical caps.  They even turned off the sprinklers a few days prior so the ground would be firm and dry for us to set up our gear.  It was fantastic!  We staked out our spot and started getting set up.

I attached my Nikon D5300 DSLR to my Borg 76mm ED refractor (via a Hotech SCA field flattener), and put the whole thing on my Celestron NexStar alt-az mount, powered by my 17 Ah power tank.  I used BackyardNikon to run the partial phase and totality scripts in serial cable mode (which takes frames every 2.5 seconds, instead of every 3.5 seconds that a USB connection does.  It's the same cable, it just talks to it differently).  I also ran my digital thermometer to record how the temperature changed.

At 10:22 AM, we had first contact!  It took another minute or two before you could see the shadow in the eclipse glasses.  I started my partial phases script a few minutes before.  However, I noticed that the images were triggering slow instead of fast, so I closed and reopened BackyardNikon.  Of course, one of my fears happened - BYN wanted to authenticate!  It does this occasionally, and it is extremely annoying, seeing as how it's a one-time fee for the software, not a subscription, and I don't always have internet access out on the observing field.  Luckily, the medical center also had open wifi, so I didn't have to fight cellular data traffic by tethering to my phone.  I got the script re-started, and it was triggering fast, thank goodness.  But a few minutes later, my other worst fear happened - my tablet randomly shut down!  Luckily, it was still near the beginning of the partial phase - I still had over an hour to get everything running.  I was glad this all happened with plenty of time to spare.  I got the tablet restarted, and I moved my telescope case with the lid open up onto the table to provide some shade for my tablet.  This seemed to help, and I got it restarted quickly.  Then, all we could do was wait.  We wandered around and looked through people's scopes, and I got a timelapse set up on my other DSLR.

As the moon covered more and more of the sun, the temperature began to drop, and the quality of the light changed.  It looked weaker, kind of more blueish-gray, like it was going behind a cloud but without the shadow.  Slowly, inexorably, the moon slid across the glowing surface of the sun, consuming it.  The Solar Eclipse Timer app on my phone announced the five minute warning, and I started recording a video on my phone, which I'd attached to one of my tripods, and then I went over to my tablet to get ready to switch scripts.  Two minutes.  My heart began to pound.  With shaking hands, I stopped the partial phase script and loaded the totality script.  One minute.  I hit the Start button on the totality script.  The darkness was coming fast now, the sun a tiny sliver.  My heart was beating so fast I felt weak and light.  Thirty seconds.  My hand was poised over the solar filter, ready to remove it.  Twenty seconds - off came the filter.  Then, all at once, darkness fell.  Cheers and shouts went up, and then the crowd fell quiet.  I removed my solar glasses and gazed in wonder at how such a sight was possible - a perfectly round, perfectly flat disk, encircled with a ring of white light, surrounded by a tenuous white glow that extended out in all directions.  Near the bottom of the glowing black disk, two brighter rays stretched out, magnetic fields lines in the corona.  Some high clouds drifted over, but could not diminish the light.  Time seemed to stretch and contract at the same time.  My phone announced that we had reached maximum eclipse, and reminded me to look around at the horizon.  I went over to my phone and panned around so I could capture it.  Sunset red and orange glowed in every direction.  The blue of the sky slid from light blue to dark blue to nearly black as I moved my eyes up the dome of the sky to the black sun.  I wished I had pulled out my binoculars so I could get a closer look, and I thought about going over to someone's telescope, but I didn't want to miss a single moment.  I stared up into the sky and burned the image into my memory.  People clapped and cheered, ooh'd and ahh'd.  "Glasses on, glasses on!" my phone announced.  I ignored its message - I wanted to see the sun re-emerge!  Westward, the sky was lightening.  Suddenly, a bright flash occurred as the sun began to return.  It was incredibly beautiful.  I put my solar glasses back on and watched the crescent rapidly increase in size.  I looked away and began to wander around in random directions.  What do I do now? I wondered.  I didn't know what to do with my hands, or where to look, so what to say.  I walked over to my camera to see how the pictures came out, and I saw a bright light on my hand - I forgot to put the solar filter back on!  I grabbed it quickly and slid it back over the end of the telescope.  Then I opened up the screen and started scrolling backwards through the extremely bright pictures at the end of the sequence.  I got back to the ones just after third contact, and I nearly fell over.  They were incredible!  The diamond ring, Bailey's beads, the chromosphere, the corona, every picture was more amazing than the last.  I had done it!  I had captured the solar eclipse with my camera!  I shouted for Sarah to come over to look.  Before long, I had a small crowd hunched over to look at my swiveled screen.  I jumped up and down a few times.  I couldn't believe it!

All right, I won't keep you waiting - here are a few of my favorites:
Partial phase - 1/2500s, ISO-200, Baader solar filter

Thin sliver - 1/2500s, ISO-200

  
Second contact diamond ring - 1/2000s, ISO-200

Corona (with some reflection off the thin high clouds) - 1/15s, ISO-200

Chromosphere and prominences - 1/2000s, ISO-200

Bailey's Beads - 1/2500s, ISO-200

Third contact diamond ring - 1/2500s, ISO-200

WOWEE WOW WOW!!  I can't get these pictures out of my head.  I get excited even thinking about them!  I am absolutely floored that I was able to do this.  

My next step now is to make a composite of the corona.  All of those solar eclipse corona images where you can see the moon and all the detail of the corona are carefully-constructed composites of multiple exposures that capture different parts of the corona - it's impossible to get the brighter center and the much much dimmer outer regions in the same exposure.  I've never done it before, so we'll see how this goes!

After totality, most people around me started packing up to try and beat the traffic, but I had planned on imaging the whole thing.  So I did what packing up I could while the moon continued to recede, and had some lunch of BBQ'd hamburgers.  After fourth contact, we got packed up, and I had the opportunity to thank the medical center administrator for letting us use the space.  Then we loaded the car, hopped in, and joined the Great American Traffic Jam.  I-25 was a disaster - there were several times where we were stopped long enough that I actually put the car in park.  We stopped in the town of Glendo along the way to use the bathroom (porta-potties had been set up there), and thank goodness I'd filled up the tank the night before because the gas station was absolutely packed.  My car has auto start-stop, so I was able to go for about 5 hours before even hitting 3/4 full tank.  We finally made it to US-26, and nearly all of the traffic on I-25 was from Colorado, so after that, the roadways were quite clear and the gas stations empty.  But it had taken us 6 hours to make it 100 miles, so we didn't get to our hotel in Kearney, NE until about 3 AM.  We nabbed about 5-1/2 hours of sleep, and then drove another full day back home.  It was a long and exhausting drive, but we got back safely.  While we were driving, moments from the eclipse kept popping back into my mind, mainly seeing the sun totally blocked out, and seeing my images right afterwards.

Big shoutout to Sarah for being an awesome travel companion, and WOW the eclipse was awesome!  You'll find me somewhere in the path of totality on April 8, 2024!

Other Eclipse Phenomena

Temperature


The temperature drop was a neat phenomenon - after restarting my computer, the first recorded temperature is at 10:50 AM, and it was 86 degrees.  I realized later that the probe was in the sun, so I moved it to the shade, and it recorded a probably more accurate temperature of 75 degrees.  In 30-second intervals, I captured the temperature up until 1:17 PM, after fourth contact.  The lowest it reached was 60.8 degrees, which was actually 7 minutes after totality.
Some clouds came in around 12:25, and it was enough to drastically dim my partial phase images by 12:40, which contributed to the decline in temperature near the end.  I think the temperature dropped more slowly before totality than it rose after totality because the day was still warming up before totality.  Neat stuff!

Pinhole Projection

When the sun passes through a small opening, you can see an image of it through that opening.  Normally we don't pay much attention - of course light going through a round hole is going to make a circle.  But when the sun is partially eclipsed, you can see that shape through small holes instead.  
Leaves on trees also make good pinhole projectors - as the sun filters through them, you can see little crescent suns on the ground in the shadow of the tree.


Sunday, August 20, 2017

#105 - Friday, August 18, 2017 - "Where the skies are not cloudy all day"

Second night out on the back side of Casper Mountain!  And I have a new toy!  At ASTROCON earlier that day, I bought a Vixen Polarie tracker.  It's a little device about the size of a large point-and-shoot camera that runs on AA's (or a USB power source) that you throw onto a tripod, aim at Polaris, and then it will track the sky wherever you aim your DSLR.  Vixen had some demo units on sale for only $200!  So I put my Nikon D5300 on it with my 50-200mm lens and did some testing.  Pointing south toward the Milky Way, and only polar-aligned using a little hole in the side (you can also get a little polarscope for it to do a more precise alignment), I was able to get at least 4 minutes at 100mm and f/5 with no star trails.  At 5 minutes, the stars started stretching a bit.  So I aimed it at Antares to image the Rho Ophiuchi complex, which I also imaged at the Texas Star Party, but with a little too long of focal length to capture as much of it as I wanted to.  I got about 30 subframes on it, but I don't have any 4-minute dark frames, so I will need to go home and take those before I can process these.

While the Polarie was going, I also set up the Borg on the NexStar mount again, but with my D3100, which lately since my old tablet's USB port is starting to go, I've been having to trigger manually with my remote shutter.  I aimed it toward M31, and there was some pretty awful periodic tracking error and what looks like the mount actually moving a giant amount for some reason, and M31 bounces all around, but I got 75 subframes on it, so it was all averaged out in the end.  The image actually came out pretty all right!
Date: 18 August 2017
Location: Casper Mountain, WY
Object: M31 Andromeda Galaxy
Camera: Nikon D3100
Telescope: Borg 76ED
Mount: Celestron NexStar SE
Accessories: Hotech SCA field flattener
Subframes: 75x30s, ISO-1600
Darks: 22
Biases: 20
Flats: 0
Temperature: 50-60F

I was hitting the remote shutter button as we walked around gazing through other people's scopes, since my shutter runs on a 2.4 GHz wifi band and can reach a few hundred feet.  We looked at the Veil Nebula, the Double Cluster, a cluster of double stars that I can't remember the name of, globular cluster M13, M27 Dumbbell Nebula, the Helix Nebula, and M31 Andromeda Galaxy.  The Veil Nebula looked fantastic through a 100-something-mm refractor, and the Helix through a large Dob with an OIII filter I could actually finally see!  I have not been able to see it before.  

Saturday, August 19, 2017

#104 - Thursday, August 17, 2017 - Pre-Eclipse Wyoming Darkness

We made it to Casper!  My friend and fellow amateur astronomer Sarah and I are here for ASTROCON and the solar eclipse!  And we made it to the remote observing site. It is on the back side of Casper Mountain, about a 45-minute drive up switchbacks and along a several-miles-long dirt road.  We got there before sunset, and I set up a timelapse to record it.  It was beautiful up there!  There was a hill near the site that we climbed up as well to get a better vantage point.  The site blocked the light from Casper to the north, and was very dark everywhere else.  It is rated dark green on the Bortle scale.

My first goal of the evening once it got dark was to try to autoguide the NexStar mount.  It connected all right, but after several attempts at calibration, I realized that it wasn’t going to work because of backlash.  I turned off the anti-backlash, and when I do that, it takes a few seconds at speed 5 or 6 to unwind the gear, so basically at guiding speeds, it was going to take a much much longer time than would work for guiding.  So I gave up and decided to do without it.  Back when I first started out, I could take 25-second images on my 8-inch SCT if I wanted to keep about 70% of them (the rest lost to periodic tracking error), and I figured I could do better with the much-shorter focal length Borg 76ED (500mm as opposed to 2000mm on the SCT).  However, I am still limited by field rotation.  Luckily, the light-mount astrophotography book I have has a nifty table with how long you can image at which altitudes and azimuths before field rotation will appear (starting with the premise that a maximum of 0.125 degrees of star movement in a single frame is acceptable).  Looking almost due south at the Milky Way, this turns out to be 30 seconds.  So that’s what I shot at.  I first imaged M17, the Swan Nebula, and then M8 and M20, the Lagoon and Trifid Nebulae together. 

While the images were going, Sarah and I wandered over to the rest of the ASTROCON attendees who were up at the site to look through their scopes.  We got some very nice views of M27 Dumbbell Nebula, M57 Ring Nebula, the Helix Nebula, M31 Andromeda Galaxy, M13 globular cluster, and I think maybe a few others, but I can’t quite remember

The wind finally died down later in the evening, but it was still chilly up at the 6,700 ft elevation with the breeze.  Sometimes a warm breeze wafted through.  We left around 1:30 AM to make the 45-minute drive down the winding dirt road back to Casper.

The images came out surprisingly well for only be 30 seconds long!  Very exciting.  It turns out to be much easier to image with the refractor, of course!  It just goes to show that aperture doesn’t always win in astrophotography.
Date: 17 August 2017
Location: Casper Mountain, WY
Object: M17 Swan Nebula
Camera: Nikon D5300
Telescope: Borg 76ED
Accessories: Hotech SCA field flattener
Mount: Celestron NexStar SE
Subframes: 95x30s (48m), ISO-1600
Darks: 20
Biases: 20
Flats: 0
Temperature: 53-55F

Date: 17 August 2017
Location: Casper Mountain, WY
Object: M8 & M20
Camera: Nikon D5300
Telescope: Borg 76ED
Accessories: Hotech SCA field flattener
Mount: Celestron NexStar SE
Subframes: 88x30s (45m), ISO-1600
Darks: 20
Biases: 20
Flats: 0
Temperature: 53-55F

The eclipse is fast-approaching, and the weather is looking promising for Monday!  I've got my BackyardNikon script all ready to go, and I spent last weekend practicing and refining the script.  Now we wait!


Tuesday, August 15, 2017

#103 - Monday, August 14, 2017 - Celestial Adventures with the Library

Christa, my Girl Scout co-leader, works at the library, and one of the other employees is working on building up a program for millennials.  I went to their game night a few weeks ago, and she asked a while back if I would do an astronomy program about the library telescopes!  The Astronomical League and many astronomy clubs have been donating small telescopes to local libraries that patrons can check out.  In the case of my local library, my astronomy club has donated two Orion Starblast 4.5's, with some modifications made.  The eyepiece and telescope caps are attached with string so they don't get lost; the eyepiece is a zoom eyepiece that is glued into place; and the CR2032 button cell battery in the red dot finder was replaced with an easily-accessible set of two AAA's, among other things.  They also come with instructions.   It's a cool program!

I spent the first half talking about the solar eclipse – what it is, where to go, and what to expect.  It was mostly cloudy, but in some parts, the clouds were thin enough that I was able to find a few double stars at least to look at.  We looked at Albireo and Mizar/Alcor.  Albireo was an easy split in these 4.5” Newtonian reflectors, but Mizar/Alcor you really had to squint.  The scopes were very easy to use, even for someone who started out on a goto mount like me.  We didn’t get to see Saturn behind the clouds until it cleared up a little more in the south, but there were still a few people left.  It was definitely recognizable – you could see the separation between the rings and the main body of the planet.  It looked quite nice, actually.  Saturn is absolutely my favorite thing to look at.  That, and globular clusters in big giant Dobs.  :)

            
Despite the clouds, I think the program was a success!  There were only a few actual “millennials” there – a lot of older folks just saw that it was a program about the eclipse or about astronomy and wanted to come – but that’s fine.  It was a good evening!

I am off to Casper, WY for ASTROCON and the solar eclipse tomorrow!  I'm bringing my Celestron NexStar alt-az mount with my Borg 76ED to image the eclipse, and I've got by BackyardNikon scripts all ready to go - one for the partial phases, and one where I'll hit the "go" button 1 minute before totality, using the Solar Eclipse Timer app for the audio cue.  One major advantage of using an alt-az mount for the eclipse is that I can plop it down wherever and not have to do much setup - no polar alignment, no alignment stars the night before, just "okay mountie here's the sun" and it'll just track it.  It's wonderful (and tested - the sun only moved one sun's-width over the course of four hours on my back porch a few weekends ago).  I was hoping to borrow a light equatorial mount from someone for taking advantage of the dark skies and doing some astro imaging, like the Celestron AVX or the CGEM or something, but 'twas not to be.  So, instead, I'm going to do a little experimentation.  Back when I was first using my NexStar mount with my 8-inch Schmidt-Cassegrain (no focal reducer), I could get about 25 seconds on a frame and only lose about 30% of them to period tracking error, vibrations, etc. However, the much-shorter focal length and much larger FOV of the Borg should be a little more forgiving, so my only limit should be field rotation.  If I can't quite get to 2 minutes in the parts of the sky where 2 minutes is possible without field rotation (I've got a table of altitudes, azimuths, and what exposure times are feasible), then it is actually possible to guide the NexStar.  PHD booted up and started talking to it no problemo.  Now whether the guiding actually works is another story - but I'll try without it first and see how things go.  Yay experiments!  I'll post all the details.  Forum posts I read were inconclusive about whether it was possible, so I'm hoping to have a nice definitive answer to that question.

The drive down will be fine, but the drive back will likely be a nightmare.  I originally planned this trip over a year ago when I wasn't sure how much time I'd be able to take off work, so we made the trip as short as we could - we're only doing Friday and Saturday of the conference, and then we're leaving right after the eclipse is over, about 2 PM Mountain time (allowing some time to pack up).  Our drive is mostly outside the path of totality, but I moved our overnight hotel stay up a few hours, and I still think we'll be getting in rather late.  And then we will have an even longer drive the second day back home.

Sunday, August 13, 2017

#102 - Saturday, August 12, 2017 - A Shorty but a Goody

It was Members Night out at the observatory, and the skies cleared up great for the Perseids!  I got set up on the memorial scope, and once it got dark enough, started firing away at the Western Veil Nebula.  I have seldom gone back to the same target with the same configuration, but mo' data is mo' betta!  So I grabbed another two hour's worth of images on it to combine with the ones I took on July 25th.  The moon rose at about 11 PM, and it started topping the trees at about 12:30 AM, which was quitting time for everyone at the observatory.  In all honesty, I don't think the result of combining this data set with the previous one was much better than the previous one alone, but I think for dimmer targets, it might prove useful.
Date: 12 August 2017
Object: Western Veil Nebula
Camera: Nikon D5300
Telescope: Vixen na140ssf
Accessories: Astronomik CLS filter
Mount: Losmandy Gemini II
Guide scope: Celestron 102mm
Guide camera: QHY5
Subframes: 32x420s (3h44m), ISO-1600 (combined with Western Veil #1, intersection mode)
Darks: 10
Biases: 20 
Flats: 20
Temperature: 58-60F

I set up my D3100 to face low Perseus to catch some of the Perseids, and a caught a couple, but only very dim ones.  We saw several pretty good ones, but they didn't brighten until they were much more southward.
You can see a reaaaallllll dim one in the top third of the frame, near the center.
Nikon D3100, 18mm @ f/3.5, 13s, ISO-3200

We had some new folks out that night as well, and some people figuring out how to use their telescopes too.  Also, my minion Miqaela borrowed my Borg 76ED to put atop her Celestron AVX.  We had some issues getting guiding to go - I'd put her camera in 2x2 bin to get better signal, but them we realized the lack of signal was because she'd left the lenscap on, but then PHD kept losing the guide star.  So I put it back to 1x1, and it seemed content with that, and guiding cleaned up significantly.  She was attempting to image the Snake Nebula, a dark nebula below Antares just west of the Milky Way.  Unfortunately, we have a lot of light pollution that direction, and she doesn't have a light pollution filter, so we'll have to see how her image comes out.


Sunday, August 6, 2017

A Super-Duper Primer of Astrophotography Part 9 - Post-Processing in Photoshop

There is lots of great freeware out there.  And I'm all about using freeware wherever I can.  Sometimes I even donate to the makers.  But there is a reason that paid software exists, and in the case of Photoshop, there are a lot of advantages for shelling out the extra dough.  I pay $10.66 a month to get some high-quality imaging processing tools at my disposal (and better yet, the license gives me 2 computers to use it on, so I can put a copy on my laptop and process while I'm at star parties, or sometimes when I'm at work).

I have Adobe Photoshop CC 2017, with Camera Raw Filter (which is like the best thing ever.)  It has a ton of tools, and I've only scratched the surface of what can be done in image processing software - some people I've met spend hours on their astro images.  I spend maybe like 20 minutes doing the post-processing.  I'm not saying that's the way it should be done, but that's about as much as I know how to do at this point!  So here's the rundown of my favorite tools.  I'll walk through processing the Rosette Nebula, since it's one of my favorite images, and a great example of what can be done with processing.

Carboni's Astronomy Tools

I mostly use Photoshop's built-in tools, but Noel Carboni developed a great set of actions for Photoshop that does some terrific things.  It's only $20, and I was able to copy the files over from my desktop to my laptop so that my laptop could have them too.  Check them out here.

The Nexus of Science and Art

There is no "right" way to process your images.  I'm going to walk through what I usually do and a variety of tools at your disposal, but this is by no means an instruction manual.  Astrophotography is where art and science meet, and no two images of the same object are exactly alike!  So do it your way.

Levels, Curves, and Auto-Settings

Many astrophotographers I've met or seen videos online of take the unprocessed image out of DeepSkyStacker (hitting the "Embed" button instead of the "Apply" button in DSS when saving the final image) and stretch it themselves in Photoshop.  I haven't really done this, and the few times I've tried were terrible, so I just let DSS do the stretching.  For the most part, I think it does a good job.  It's also a lot easier to white balance in DSS when you can visually move the RGB curves on top of each other.  (See my stacking tutorial for information on this).  So I'll skip the histogram stretching, and we'll start with the image I left off with in the stacking tutorial post of the Rosette Nebula.

First, import into Photoshop (the TIFF) - I usually just click and drag, but you can also go to File -> Open.

The first thing I usually do is try Photoshop's "Auto" tools, under the Image menu.  There is Auto Tone, Auto Contrast, and Auto Color.  Sometimes these work great, but sometimes they make the colors funky, or blow out the cores of galaxies, or make the noise level go through the roof.  You can always hit Ctrl+Z to undo.  In this case, they worked rather well.

My next stop is the Curves window, which you can access either by going to Image -> Adjustments -> Curves, or using the shortcut Ctrl+M.  You will see a window with a histogram and a luminance line.  Since the Auto tools did a good job, my histogram is already pulled all the way over to the left.  Sometimes, though, especially when your light pollution is high, the background can still have a lot of light - this will show up as a gap between the left side of the histogram plot and the peak that represents your data.  Take the dot at the bottom left corner of the diagonal line and drag it to the right.  Go far enough to reduce your background light, but not so far that you start losing the dim details of your DSO.  

Next, you can increase the brightness of your DSO by clicking about two-thirds of the way up the diagonal line or so and dragging it up.  Don't overdo it, but this can help bring out dim objects.

I like to click "OK" between actions - that way, it's easier to undo them one by one instead of undoing them all at once if you decide you don't like it.  The next thing to do here is to set your black point - I usually only do this if the white balance still isn't quite there.  You can do it by clicking on the leftmost eyedropper (just to the right of the "Input" box), and then clicking on a black area of your picture.  You might have to try different places because a pixel that appears black could really be a colored noise pixel, in which case your white balance could get very weird.

In addition to adjusting the master histogram, you can adjust the histogram for each channel by clicking on the box next to "Channel" and choosing Red, Green, or Blue.  I find this helpful when my background is more reddish or greenish or blueish, or when I need to bump up the red in a given object because unmodified DSLRs are not great at imaging red.

Feel free to mess around here until you are satisfied.  You can always undo actions by going to Edit -> Step Backward, or clicking on the History button (see below screenshot).

Astronomy Tools

At this point, I'll apply some of those astronomy tools I mentioned from Carboni.  The 5-inch refractor I frequently image on is not an apochromatic refractor, but a neo-achromat - it has less chromatic aberration, but it's not entirely corrected.  So my stars will often have little blue-violet halos around them.  Not to worry, there's a tool for that: the "Reduce Small Blue/Violet Halos" tool.  Works like a charm, and so far I haven't seen it have any affect on the rest of the image.  To run a tool, click on it, and then click the "Play" triangle button just below.

For images with a lot of light pollution, I'll usually run the "Light Pollution Removal" tool next.  The readme that comes with the toolkit explains how to do this, but I'll show you here too because I'm feeling generous.  After you hit the Play button, it will think for a bit, and then a "Dust & Scratches" dialog window will appear that will make your image look very fuzzy.  Not to worry, it'll return to normal once you're done.  Slide the "Radius" slider until the largest stars just disappear, then click OK.

It'll think some more, and then present you with a familiar window - the Curves window.  Click on the leftmost eyedropper, the "Set black point" one, and click on a place in the picture with the most light pollution.  You might need to click around until most of the light pollution is gone, but none of the DSO.  Then click OK again.  Once it's done thinking, you should have an image with a nice dark background!  The white balance might be off, so run the Curves tool again with the "set black point" eyedropper to adjust.



There are lots of other tools here - give them a try!  The documentation with the toolkit explains them pretty well, and there is more explanation + examples on the website.


Quick note:

If I come to a point along the way with a good-looking image, I'll save it, and then keep editing.  Then, when I'm all done, I'll pick my favorite iteration.  Sometimes, it's the one with less editing done that ends up being the winner.

Camera Raw Filter

This is probably my favorite part of Photoshop!  It's a fantastic tool for editing raw daytime images, but you can also edit JPGs and TIFs and whatever else with it too.  It's under Filter -> Camera Raw Filter, or the shortcut is Ctrl + Shift + A.
If you use a light pollution filter on a galaxy, this is a good place to adjust the white balance by adjusting the "Temperature" and "Tint" sliders.  I usually also increase the contrast a bit, lower the blacks (which basically chops off the left part of your histogram - you can lose some faint detail here, but gain a nice black background.  Try to find some middle ground), and increase the saturation.  Mess around with the sliders until you get something you like.  Don't go too crazy - it's easy to introduce noise or lose detail by going too far with any of the sliders.

Under the histogram, there are a series of tabs marked with icons.  The first tab is the one shown in the above screenshot, with the basic adjustments.  The second tab is just like the Curves tool, where you can adjust the luminance line for all channels or each individual color channel.  You can also select Parametric instead of Point and adjust each section of the histogram independently - Highlights, Lights, Darks, and Shadows.  It gives you a lot of control.

The third tab is probably my favorite - it has an excellent noise-reduction algorithm.  I never use the one under Filter -> Noise because I don't think it works as well.  This one is fantastic.  There are two sliders you'll focus on - Color and Luminance.  Start by zooming in - I usually go to 100%.  The tutorial I used to learn about this tool said to put color nearish the middle (I never see it do much on its own), and then move the Luminance slider up far enough to reduce the noise, but not so far as to start losing detail or get weird artifacts.  
Isn't it magical??
The Astronomy Tools toolkit also has three noise reduction algorithms - Space Noise Reduction, Deep Space Noise Reduction, and Less Crunchy More Fuzzy.  

So that's about all I usually do for my typical astrophotos.  Sometimes they require some special care if the noise profiles are particularly high, or they are resisting being white-balanced, etc.  But these are the basics!  Definitely explore the plethora of other features in Photoshop, and hit up all of those internet tutorials.  And then enjoy your gorgeous photos!