Shooting with an Astro-DSLR in the Atacama Desert

mo.jpg

by Molly Wakeling (Astronomolly)

Trip of a Lifetime

For the first two weeks of July 2019, I had the grand opportunity to take a vacation to northern Chile. It was an incredible trip! The small group of us from my astronomy club had two goals: see the July 2nd solar eclipse, and observe the Southern skies from the dark, high-altitude air of the Atacama Desert.

We spent the first week in Santiago and La Serena, and we watched the eclipse from the village of La Higuera, about 50 km north of the coastal town of La Serena. It was an incredible experience, especially when shared with some 250,000 people who flooded the area! The second week we spent at the Atacama Lodge, just south of the touristy village of San Pedro de Atacama in the northern part of Chile. The Atacama Lodge is owned by French expat Alain Maury, who maintains several robotic telescopes and offers nightly tours to buses of people in his sunflower field of home-built Dobsonians. You can also stay in one of the adobe cabins on-site, and rent a telescope for yourself. I had rented an imaging rig (which he usually doesn’t do, but I convinced him I knew what I was doing), but some power issues with the mount left me using my own gear most of the week. I had brought down my Nikon D5300, Sky-Watcher Star Adventurer DSLR tracking mount, and three lenses: the stock 18-55mm f/3.5 lens, an older 70-300mm f/4-5.6 lens, and a new 35mm f/1.8 lens I had just purchased before the trip.

I have kept a log of all of my astronomy nights since I started the hobby back in July 2015; this is night #197, which was my third dark, steady, cloudless night at the Atacama Lodge.

Daytime Excursions

I managed once again to sleep in until 12:45 PM, and thank goodness! I was starting to feel more adjusted to the altitude (7800’), and my two traveling companions (John and Beth) and I felt ready to go do some daytime exploring. So I copied last night's data off of my memory cards, drank a hearty cup of coffee, and we left at 2:30 PM to go to dome sightseeing. Our first stop was the Valle de la Luna, or "Valley of the Moon," but they only allow car entry between 8 AM and 1 PM, so we missed our chance. Try again tomorrow...so instead we set our GPS for one of the sites in the salt flats, Salar de Atacama. On the highway, we crossed the line of the Tropic of Capricorn!

Salar de Atacama was both the name of the general area, and supposedly a particular lagoon in the salt flats. Unlike salt flats in other parts of the world, the one here in the Atacama Desert was not really that flat. Well, the landscape was flat, but the salt formed stalagmites that stuck up out of the ground! We pulled off to give it a closer look, and it was extremely hard stuff. The salt chunks were also very sharp -- I was glad I had my hiking boots on with Vibram soles. It also sounded hollow in places. John used his Leatherman and some other tools he had in his pockets to bang on the crystalline structures, and with the different tones, he was making some music! It was very cool and also very strange.

We wound up not finding a particular location or lagoon of Salar de Atacama, so we drove back northward to try Laguna Cejar. But my phone's GPS said we wouldn't get there till 6:30 -- after sunset. So we just drove back to the Atacama Lodge instead. A day of bad luck! But the drive was gorgeous, at least. There were rocks strewn everywhere from volcanic eruptions, and there were some places where the road was washed out due to an earthquake re-routing a stream and launching all kinds of water down the mountain. We also passed by the entrance to the radio telescope array ALMA, and we could see the workshop from the road.

Borrowing an Awesome Camera

Once we got back to the lodge, I went and found Alain to ask for help re-polar-aligning my Sky-Watcher Star Adventurer again once it got dark, and to get a status update on the Sky-Watcher AZEQ6 mount I was supposed to be borrowing, but it had quit working. He said since he couldn't fix it right away, I could instead borrow an astro-modified Sony a7s with a Rokinon 135mm f/2 lens! I was so all over that. Astro-modified means that a standard DSLR camera has had its spectrum filter removed. Consumer cameras have a special filter on the camera chip that passes the different wavelengths of visible light at different amounts in a way that matches how the human eye responds to color. This way, images come out looking mostly like how you saw them in real life. However, the human eye is not particularly sensitive to red, which unfortunately is what a lot of the objects in the universe emit, especially nebulae. With the spectrum filter removed, far more red light can make it to the camera chip, which increases your signal-to-noise ratio at those wavelengths by quite a bit. I've seen some amazing images from astro-modified DSLRs. I've thought about doing it myself, but I think I'll save the money and get a color astro camera instead (such as the ZWO ASI1600MC, the color version of my ASI1600MM Pro) so that I can also have the cooling system.

We had a few issues at the start getting it rolling though. It had one of those spare battery and memory card compartments attached to it, and for some reason it wasn't liking some of the batteries. So we finally put just one battery in instead of two, and it seemed happier. Then, when I was scrolling through the menu options (after having Alain help me change it from French to English), it kept seeming to push

buttons on its own! Finally I called Alain over to take a look, and he just gave me another astro-modified Sony a7s to use instead. That one seemed to work.

The Sony a7s is a mirrorless camera, meaning that much like point-and-shoot cameras and video cameras, the viewfinder is electronic.

In order to actually see anything, the image gets stretched quite a bit, so it was far easier to get the camera pointed at what I want, since I could see it on the screen so easily! It also went up to stupidly high ISO values, like 64,000 (not 6400, 64,000!).

Now, the Sky-Watcher Star Adventurer actually has two camera-connection screws: one on top of the declination adjustment plate, and one further down on the dovetail. So what did I do? You guessed it – I put both DSLRs on it: the Sony a7s, and my own Nikon D5300! Actually, having the D5300 in the lower camera spot, which is toward the middle of the camera-counterweight balance point, helped balance it, which was perfect. The only issue I ran into was that I had to point the cameras carefully, since they would run into each other. It meant I couldn't quite point both where I wanted to, but I got close enough. I wound up swapping out the 300mm lens for the 35mm to avoid problems.

moll4.jpg

It was a challenge to focus the Rokinon lens since the focus point was very tight, but I finally got close, and then pointed the Sony toward the Eta Carinae Nebula and Running Chicken Nebula (Lambda Centauri cluster) area. I had to rotate it sideways to avoid seeing a refractor at the front of the shed. (This particular refractor belonged to the author of the BackyardNikon and BackyardEOS software!) I set the exposure time to 30s because even at ISO-1600, one minute was overexposing the image! The images looked very red due to the lack of spectrum filter, but that will all come out in processing. Then

I pointed the D5300 up to the Rho Ophiuchi region, which took a while to finesse into place so that I could get the most of the dust clouds, but not also get super-bright Jupiter in the scene.

Visual Observing

I am an astrophotographers to the core, but I do enjoy letting the photons strike my eyeball directly once in a while, especially under dark skies through big juicy Dobs. Once my cameras were all set and rolling, I wandered back over to the scopes to see what John and Beth were up to. John had a 28-inch Dob looking up at Jupiter, which was incredible in the eyepiece! So bright, and so much detail. It's so much higher in the sky at 22° S latitude than it is up in the US, plus the skies were very clear and steady. It was breezy out, which made the Chilean winter air feel much colder, and the moon was still up and brightening the sky, so we went inside to warm up and wait for it to set. In the meantime, we worked through some wine we had bought and needed to finish before we left on Thursday.

I went back to the shed later to swap batteries and re-position cameras, including on my Nikon D3100, which I had set up on my mini-tripod to do star trails/timelapse facing south over the robotic scope domes.

Then it was back to more visual observing -- M25 open cluster, Sculptor/Silver Dollar Galaxy again, NGC 1365, Stephan's Quintet, more Tarantula Nebula, and more 47 Tucanae. NGC 1365 is a gorgeous barred spiral galaxy in the constellation Fornax, and I could see its shape! Very very cool. It's about 60 million lightyears away. I also tried to find the Bug Nebula, but was unsuccessful. Giant globular cluster 47 Tucanae was truly a sight to behold! In the large Dobs, it displayed seemingly thousands of individual glittering stars that seemed to swirl around a central point right before your eyes.

The true crown jewel of the southern sky, however, is the Tarantula Nebula. With how steady the skies were, you could put a high-magnification eyepiece on one of the Dobs and lose nothing, but gain so

much.

moll5.jpg

That, combined with an OIII filter, made the Tarantula Nebula actually take my breath away. First of all, it was enormous. It is difficult to believe that it belongs to another galaxy! It also sported a great deal of structure and depth. It looked like you could fall into it, and it would catch you like a trampoline. We looked at it many times that week, although we had to stay up until after 3:30 AM to see it!

Back to Imaging

At some point, I went back over to the shed and changed the Sony to imaging the Large Magellanic Cloud, and the D5300 over to both Magellanic Clouds with its 35mm lens.

Large Magellanic Cloud single frame at f/2,  ISO-1600, 30s  Don't worry, the red will process out...

Large Magellanic Cloud single frame at f/2,

ISO-1600, 30s

Don't worry, the red will process out...

After over an hour of imaging at those spots, I discovered that I had accidentally left the D5300 set on 10s instead of Bulb from when I was centering the Magellanic Clouds! It had been imaging for quite a while at that point, but I switched it back to Bulb anyway for the 60s images I had set on the intervalometer.

At 5 AM, I was tired and ready for bed, but since it was still dark until about 6 AM, I left the cameras running this time. I had started the Sky-Watcher far enough east that I was pretty sure it wouldn't hit the mount before I woke up to shut off the power, and the shed would close at sunrise to protect from the sun (I was pointing south anyway, away from the sun). Plus, the batteries would die at some point. So I left it running and went to bed.

Another fabulous night (and day)!

moll0.jpg