Astrophotography - the journey so far
September 28, 2015
The urge to sleep creeps up. There goes another off-brand energy drink. Health habits, not my strong suit; nor keeping in touch with old friends. We’re playing Civilization: Beyond Earth to kill the time. It’s almost 3 AM. I hadn’t spoken with him in a while, but tonight is the blood moon lunar eclipse. It’s a rare astronomical phenomenon, the earth will be directly in between the sun and the moon. This will cause earth to cast a shadow on the moon, a full lunar eclipse. The moon will appear red, due to the atmospheric diffraction, like a sunset. More unusually, since the moon will be very close to earth it will also appear larger than normal. It’s a good reason to catch up with old friends, a good reason to share an interest in astronomy. More people will join, and someone might bring a telescope. 4 AM, It’s almost time. We grab our coats and go for a short drive to a dark site on a levy in Friesland, away from the light pollution.
The view is stunning. I have never seen this many stars before. I have actually never seen a lunar eclipse before. Kid growing up in the city, I guess. It is truly stunning. I try to take some pictures with my Canon on a tripod, but it’s no good with the short focal-length lenses I have.
Luckily, one of the guys brought the telescope. I know absolutely nothing about them, but we manage to attach my camera to the back. It’s a pain to focus, but there it is. A photo of the blood moon.
I’m excited. Very excited. I ask him what the telescope had cost. “Oh about 50 bucks second hand”. Somehow I always thought they would be more expensive. “I’m getting one” my tired brain responds. Little did I know, how far down the rabbit hole would go.
March 13, 2016
It had been a while since that blood moon illuminated night on the levy. It’s a stretch to say I’ve always been interested in astronomy. More accurately, I guess, I’ve always been interested in science-fiction. I grew up with the Thunderbirds, Star Trek, and Babylon 5. The scenery and technobabble strike a particular part of my brain that makes me truly love it. Maybe it is part of the nerd disease. But astronomy per se, no, not really. The only time I looked through a telescope was at a high school astronomy class, but that was mostly an excuse for covert underage drinking.
I’m too young to remember the golden space age, the days of moon landings were long gone when I was a child. Vaguely I recall having a newspaper clipping of the Hubble Space Telescope image “pillars of creation” as a kid, but I don’t think I ever grasped the significance; just thought the pictures were pretty.
Pretty pictures, though, drew me to /r/astrophotography, a site where people post their homemade pictures of stars, nebulae, and galaxies. And they are, without a doubt, very pretty. Some of these pictures turned out to be taken with a simple lens and camera. I’ve been “doing” photography for, oh, 18 years now? Can’t be that hard. I grab my Canon 5DmII, Carl Zeiss 85mm, and bicycle. It’s about a 20 minute ride to get outside of the city, away from the worst light pollution.
Now, I know very little about stellar cartography (see, told you I like technobabble), but with the Stellarium iPhone app I find the Great Nebula of Orion. From what I had read on the internet the nebula is a particularly easy thing to photograph. There are a couple of things you have to know: it is very faint, so you need a long exposure to see it, but since the earth rotates on its axis (giving day and night) you need to keep your exposures short to avoid getting a trail of stars. Dilemma: star trails with long exposure, or short exposure without seeing the nebula. Turns out there is a trick: take many short exposures, and overlay them together with a computer (a technique called stacking). To calculate the maximum exposure time without getting star trails, divide 500 by your focal length (rule of 500). So in my case 500/85mm = 5.8 seconds. I set it to 5 seconds. Another problem arises: even with short exposures the constellations will move across the sky over time. You usually don’t notice it, but the stars move rather quickly! Putting up a tripod, taking a lot of 5 second exposures won’t work: the stars will gently drift further and further. Taking no chances, I slightly bump my tripod every 5 minutes or so making sure the same place is still in the middle. An hour passes, fiddling with buttons and knobs. I go home.
A blanket of warmth greets me at the door. I grab a cold beer and fire up PixInsight for the first time. It’s a bit expensive, but it seemed to be the best thing since sliced bread according to the internet. So I just went ahead and bought it. I mean, life is too short to learn crappy software, better pay some money to get the good stuff. Manuals, lots of manuals.
The basic procedure seems simple. Since you take long exposures, you get noise. Noise is terrible, so you want to get rid of it. There’s a trick: you take pictures with the lens cap on. Taking pictures while making sure no light gets in allows you to capture the noise pattern of your sensor. Two types of noise have to be dealt with: the inherent noise pattern of the sensor (called sensor bias), and the noise from doing the long exposure (dark noise, due to heat building up in the sensor). Bias noise you can get rid of by taking images at the shortest possible exposure, dark noise by taking images equally long as your original exposures (called “lights”); both with the cap on. The images collectively are referred to as “subs” (for sub-exposures). Ideally, you create all the subs with the same temperature and settings so the noise patterns are identical. You take the bias and dark subs, average them out to create a “master dark” and “master bias”, and then “calibrate” your images with them. Then you’re left with a bunch of relatively noise free images that are all slightly different. By applying “star alignment” image registration, all of your images will know the position of their stars, and how to transform the image so it will perfectly overlap with a reference image. The calibrated and star aligned lights can then be “integrated”, basically taking the mean value of all the pixels in the images. Of course, it’s more complicated than that if you want to prevent airplanes, meteorites, some clouds, and cosmic rays ruining your images, but this is the basic idea. After image integration, you have a very dark image with nothing to see.
Space is dark, although you have to wonder why with all the stars. To see something “real” you will have to boost the dark bits of the image by making them lighter, this is called “histogram stretching” (or simply “stretching”). This is more art than science, you just fiddle with the check boxes, sliders, and graphs until you get something pretty. (I talk like I know what I was doing, but I really wasn’t.) There it was, my first Deep Space Object photo. The Orion nebula, from just outside a densely populated area in the Netherlands, some 1344 light years away.
Often I get the question: “did you see this?”. The answer is “no”, you see almost nothing with the naked eye. Our eyes and brains aren’t wired for long-exposures. In some ways the camera is more sensitive than our eyes, the aperture is larger, the sensor uses different technology than our neurons, and you can take hours of exposures.
“Is it ‘real’ then?” some people ask. That’s a matter of perspective I guess: a microscope sees things we can’t see either, and yet the things are “there”. It’s about making the invisible “visible”. The colors are mostly “fake” though, you just come up with something pretty. Colors are subjective anyway.
“So what would you see if you were there, with a spaceship?”… pretty much nothing. The nebula is like a thin fog, particles of dust spanning thousands of light years. If you were to stand “inside” the nebula it would be pretty empty, and visually not much different from the rest of space. In fact, we know that our own solar system has some nebulousity, maybe to a distant civilization our patch of space is a beautiful thing to photograph. Who knows.
The prospect of “seeing” the invisible excites me. I really need to get a telescope.
April - May 2016
The hunt was on for a good telescope. To be honest, I know nothing about telescopes. Refractors, Reflectors, Newtonian, Apochromatic (APO), Schmidt-Cassegrain, Schmidt camera. It seemed so long ago that I shot the blood moon through my friends small non-APO refractor. I had to become acquainted with all the jargon, and fast. Polar Alignment, Guiding, Equatorial, Alt-Azimuth, CCD, CMOS, Bayer Mask, Narrow Band, LPS/CLS… the list never seemed to end. Countless hours of reading and putting stuff in shopping carts but never hitting “checkout”. There are a couple of important parts when doing astrophotography:
- The mount. This is a motorized machine on a tripod that allows whatever is attached to it to accurately track the sky. Basically, it counteracts the rotation of the earth. Ideally you spend some good money on your mount, it will determine the quality of all your photos. The best type of mount for Deep Space Astrophotography is an Equatorial mount, which has four degrees of freedom: altitude, azimuth, right ascension, and declination. By aligning the mount perfectly with the North Celestial Pole (roughly where Polaris is) using altitude and azimuth, the other two axis (RA and DEC) can track anything in the sky. For astrophotography it is definitely worth the upgrade to get a mount that you can attach to your computer.
- The telescope (or OTA for Optical Tube Assembly). There are several telescope designs. However, their goal is always the same: capture a lot of light at a long focal length, so things appear closer and brighter than with the naked eye. What telescope to get is a bit of a trade-off. But starting out with a relatively wide and fast apochromatic refractor works very well. Another commonly used telescope is the Schmidt-Cassegrain reflector, but it can be a bit more involved to use.
- The camera. It is perfectly possible to capture Deep Space Objects with a normal camera, like a Canon 450D. You’ll need an adapter for the telescope-camera combination, but almost all brands are supported. If you want to do it properly, however, you need to get a cooled monochrome CCD. Normal consumer cameras use CMOS sensors, which can be more sensitive but also have more noise artifacts. CCDs are true scientific instruments, and often have a better dynamic range than their CMOS counterparts. Consumer cameras also apply aggressive filtering on some wavelengths that are uncommon in the usual images, to make them appear more “natural”, but those filtered red and near-infrared wavelengths are useful for astrophotography. You can modify most dSLRs to remove or replace the filter, but at that point you may want to get a dedicated camera anyway. Astrophotography cameras can also come with a peltier cooled sensor, which greatly reduces thermal (dark) noise and keeps your images consistent. Some can even cool as far as -40ºC below ambient temperature.
- Filters. I mentioned that you’ll want to get a monochrome camera. This seems silly, since usually you don’t want black & white photos (although probably very Instagram worthy). To understand why monochrome is better, you’ll have to understand a bit of how a normal camera captures color. Basically, it doesn’t. Any camera is a monochrome camera. On top of each of the pixels there is either a red, green, or blue filter. The filters are arranged in a hexagonal pattern, usually in RGGB, called the Bayer Mask. This Bayer mask means only 25% of the megapixels in your camera can see red or blue! Software trickery gives all the pixels a color by interpolating the neighboring red, green, and blue pixels (a process called debayering) so it appears as color; but you lose a lot of resolution along the way. If you want to use all the megapixels, you use a monochrome camera and your own filters. By switching out the filters in sequence you truly get the amount of megapixels you payed for, and by using software you can combine them back into a color image however you like. More interestingly, a lot of the nebulas emit light at very specific wavelengths. Filters exist that only let those wavelengths through, called narrow band filters. Not only are they great for combating light pollution, since the street lights emit at different wavelengths, most of the cool NASA photos are done with a series of narrow band filters too!
- Guiding. Polar alignment is a pain, plus any mount will have a certain amount of error when tracking. To make the tracking more accurate you can use a guide scope. Basically, attach another telescope with another camera on top of your imaging setup. The guide scope can then accurately track a star (called a guide star). The software looking at this guide star can then send corrections to the mount (using guide pulses) to make sure it stays put, compensating for misalignment and drift.
Amazon checkout. Placed an order for an Orion Sirius EQ-G motorized equatorial mount. I did it. The first step. And, there it was, 20 kg of equipment. And I can’t drive. You can’t really take this stuff on a bicycle either, even if it’s “just” 20kg. This stuff is huge and bulky. Setting it up in the back yard? No way. I don’t have a view on anything. Crap.
I call my parents, they have a small vacation home just outside of Groningen. Being slightly embarrassed (being 28) I ask: “can I stash my telescope at your vacation home”. To my surprise, they agreed. And I went on to buy a ridiculous amount of gear. This stuff tends to explode. So you want a telescope, then you need guiding, so you want to do Hyperstar imaging, then you need a CCD, have a CCD get a 12 volt battery, have a 12v battery get a voltage stabilizer… I could sum up all the expensive mistakes I made along the way, from a Samyang mirror lens to the QHY10-OSC, but I guess it’s fair to say at this point it is far from the “50 bucks or so” my friend quoted. I got lost in the forest of gadgets, gear, and gear heads; lost in wanting the best “in theory” and never using it. In the end I got a Celestron Edge HD 8“, Orion Starshoot mini auto-guider, FeatherTouch, Hyperstar 3, QHY10 OSC, Optlong CLS filter, RigRunner power distributor, Deep Cycle 12v battery, USB hub, voltage stabilizer, and a lot cables. All theory and no praxis. Lost.
Here’s the thing about Dutch summers: they don’t get dark. Anyone I tell this look at me like I’m crazy. But it is true: of course it gets darker in the summer, but not proper dark. Perpetual twilight at N 53º. From May till September we have no astro darkness. The sun sets, but it never gets proper dark. Which is killing for astrophotography, since you really have to take those long exposures. Not to mention that even with insomnia waiting till 1 AM for slight darkness that maybe ends at 1:30AM is a bit too much. So between 3 months of having no darkness, and 12 months of only having clouds: the Netherlands is the dumbest place on earth for this hobby. But having bought a decent amount of gear and having it stashed at my parents vacation home: I was of course itching to try it.
So I pack my stuff and go, knowing that this is my last chance before summer fully sets in. I mess up badly. Can’t get polar aligned. Pulled a muscle from the now 50 kg of gear, and clouds move over. Next day I try again, mess up the polar alignment again, and everything is soaking wet from the dew. We usually think of heat as moving through a medium (convection), but at night a lot of heat actually radiates into space. That is why it’s colder at night than during the day: it’s not the atmosphere moving, it is the heat that was captured from the sun that is radiating out into space. Turns out that putting a telescope in a field is a perfect way of building a “cold sink”, and when the telescope reaches the condensation temperature of water dew will form. The larger the telescope, the more dew will form. And everything was soaking wet. One way of fixing this is by applying heat to the telescope. But you have to be gentle: otherwise you get turbulent air, distorting your image. I got a dew shield and a dew heater. But I badly mess up polar alignment again, lost my USB hub in the dark even though it’s a full moon and you can read a book in that light. For the first time, being alone in that field, with no one to talk to, dragging 50kg of equipment 400 meters to a clear field: I cry. I call my girlfriend, telling her I’m lonely. Why is this so hard. Why can’t anything work I want it to. All theory, and no praxis. And I am alone in a field. I drag my equipment back, putting in the silica balls everywhere to prevent condensation building up and I try to sleep.
The thing is, you don’t give up. You try again. And again. And again.
Astrophotographers call this “first light”. The first (successful) capture with new equipment. At this point I wasn’t sure if I was excited, or relieved. Relieved that, even though a lot of it was wrong, I managed to produce something.
I never got to use that vacation home again. My girlfriend and I broke up after 6 years. I had to move out of the house, and started living with my parents until I found a new apartment. They brought my telescope there. Some things maybe aren’t meant to be. Some things, like living on 28m2 24/7 for 5 years, take a toll. Some things, even though you love them, you can’t go on doing. To love is to let go. It has only been a couple of months.
The night sky has no memory of your mistakes. Polar alignment you can try again, or just buy a PoleMaster. Sometimes, I wish I had a PoleMaster for my heart.
My parents have a garden, which doesn’t have a very good view on anything astro-related. Except it does have a view on Polaris. So I can polar align, and anything I can point the scope at is fair game at that point. Keep my mind off of things.
During that month of living with my parents, not something I am proud of, I learned the value of easy access to an imaging site (among other non-astro related things). Even though it wasn’t ideal, I got 4 nights of clear skies. I got guiding to work with PHD (sounds smart, but stands for “Push Here Dummy”), plate solving go-to using Astrometry.net, the COM port drivers for ASCOM, collimating the Hyperstar, and many other nuances. Most importantly, the realization that most annoyances come from misbehaving hardware and software: praxis, not theory. Keep doing. Looking for apartments I specifically went looking for one with an open view roof terrace.
Finally I moved to my new apartment. Everything is Ikea. I feel like Edward Norton from Fight club. By buying more random furniture I try to de-Ikea it, but that never works. Some nights are clear, and I wonder if it is worth going up the stairs. But I am tired and disoriented. I have to move the 50kg of equipment four flights of stairs up to an extremely light polluted city sky (Bortle 9). This can’t possibly work.
Out of focus. sigh.
I bought a mono camera (ZWO 1600MM-Cool CMOS) for narrow band imaging, considering buying an auto focus stepper motor. Here’s the thing: I’ll just try again. With better gear and more knowledge. Maybe I’ll get that image of M16/NGC 6611 (the Eagle Nebula) in SHO (SII, H-alpha, OIII) narrow-band, with the “pillars of creation”. Maybe, one day, I’ll get the Heart and Soul as a mosaic; a reminder. That is, if these clouds will finally move.