The Art of Space Photography
Andre van der Hoeven fell in love with space after watching the first Space Shuttle launch in 1981 at Kennedy Space Center. He trained as an aerospace engineer and is now an astronomy teacher in the Netherlands, where he also practices the art of deep sky astrophotography.
After winning 2nd place in NASA’s Hubble Hidden Treasures contest, he’s compiling a photobook of amateur and professional space photography. For Polarr, Emily von Hoffmann spoke with Andre about some of the tips and tricks he’s learned.
Emily von Hoffmann: When did you become interested in space?
Andre van der Hoeven: I’ve been interested in space since I was about 4 years old — I still remember the first Shuttle Launch, and even still have at home the newspaper articles from that time. Until my 18th year (when I started studying as an engineer) I was quite active in this field, but then I lost the hobby and didn’t really pick it up again until 2010. That year I was asked to make lessons about astronomy at the school where I work, so I began gathering materials for that. When browsing online I saw great images pass by and decided that I wanted to do this kind of imaging myself. That’s the moment when I bought my first telescope and started learning astrophotography.
EvH: Did you have experience in other genres of photography?
AvdH: When I was young (about 15 years old) I was already member of a photo society. Photography has always been a favorite activity of mine, especially landscape photography. When I bought the telescope, an old specialized ccd camera was included. One evening I decided to try to take some images and took M51, the Whirlpool galaxy, as my first target. When seeing the spiral arms appear on my computer screen I was totally impressed and decided to continue with this. During my studies I worked for three months at the Technical University in Prague, where I worked with Landsat satellite imagery. There I learned a lot of the techniques behind multi-channel imaging that helped me a lot in the field of astro-imaging, because a lot of the techniques are comparable.
“Sometimes there are prolonged periods of bad weather and as such it can happen that an object that you started to image is not in view anymore when the weather clears. This means that sometimes an image can take more than a year to gather all the needed data.”
EvH: What are some logistical challenges of shooting scenes in space, compared to snapping an image on the street, for example?
AvdH: The biggest problem is time and weather. For space imaging a lot of time is needed. The objects are often very weak in the amount of light they emit and so you have to expose for long times (think of exposure times up to 30 minutes). Next to that you need to take many of these image to reduce noise in the images while boosting the signal. This gives rise to some logistical problems. You need a place where you can put up your equipment safely for a long time and also with a free view on the sky, because the objects move during the night and you have to try to keep them in sight. So you have to prepare your imaging session carefully and check where the object is in the sky during the imaging run. It’s not like making a snapshot.
Another issue is weather. Sometimes there are prolonged periods of bad weather and as such it can happen that an object that you started to image is not in view anymore when the weather clears. This means that sometimes an image can take more than a year to gather all the needed data.
Furthermore we use black/white ccd cameras, where color filters are put in front to image the different color channels. So you need to plan ahead when to image with which filter, and make sure that you get data in all the three color channels (r,g,b) and sometimes also in specialized narrowband channels (like the so-called h-alpha channel, which is emitted by glowing clouds of hydrogen gas in space). There is nothing so frustrating as having finished two out of three channels when clouds come in and not being able to image for the next few weeks.
EvH: What are some useful techniques for astro-imaging that you’ve learned over time?
AvdH: For deep sky astro-images I use a specialized CCD camera. This camera is cooled to minus 20 degrees C to make the noise as low as possible. The camera that I use is of the QSI brand, which is a company that specializes in this kind of camera. Furthermore, the camera has a built-in filter wheel that can be controlled by computer. The two most important techniques that I use in astro-imaging are called stacking and stretching.
Stacking means that you take many images of the same region. Every image has a certain amount of noise generated by the camera and the sky background. By overlaying these images on top of each other and averaging them you can boost up the signal (which is the same in all images) and reduce the noise (which is random and therefore different in every image). This technique is also very well suited for night photography of static objects, but is not very often used because it is not so well-known.
The other technique is called stretching. Because the signal is very weak it is often only present in the lower part of the histogram of an image. By gradually increasing the brightness of the lower part using curves you can make a lot of the ‘hidden’ signal visible. This procedure we call stretching, and how you do this is very important for the quality of the final result.
“What is astonishing if you think about the fact that you are looking at 100 billion stars, each with their own planets. What I always think to myself is, if there was somebody in that galaxy looking at the same time towards our galaxy, what a sight that would be.”
EvH: How do you find these scenes or events in space to photograph? Are they things that you have to move quickly to capture, or do you usually kind of see them coming?
AvdH: Most of the images I’m able to prepare for. I have a program in the computer where you can simulate the view of your telescope. So I select an object and then look in the program to see how it fits in my telescope’s field of view. In the program you can also find the rotation angle of the camera that gives the nicest composition. Then you get coordinates and a camera angle to aim at. For this kind of imagery I need about 30–45 minutes to set up and start the equipment. But when it runs and everything goes well, you can just leave it and the computer will normally control it.
Sometimes there are objects that have much shorter life-span or are moving fast in the sky, like comets. For these kind of objects more pressure is present and you have to act faster. Weather is often the limiting factor.
EvH: What are some of your favorite images from your project?
AvdH: The first image that I like a lot is my image of M31, the Andromeda galaxy. This is the closest galaxy to our Milky Way and I think it is a very impressive sight. What is astonishing if you think about the fact that you are looking at 100 billion stars, each with their own planets. With a telescope like I use (which is not so big, just a 9cm refractor) you can discern globular clusters that are surrounding this galaxy. What I always think about is, if there was somebody in that galaxy looking at the same time towards our galaxy, what a sight that would be.
The second image that I like a lot is an image I took last summer of the Milky Way. During the capturing of these images, a meteor exploded exactly in the field of view and left a bright trail. This is not uncommon, but a week later on Facebook I saw an image of somebody showing a sort of contrail caused by a meteor. I decided to look again at my images and noticed a faint dust cloud coming from the place where the trail was visible. For me that was a very special image because it really showed something that I had never seen before, and which shows how nice these kind of effects are.
EvH: What is something rare or exciting in space that you would like to capture?
AvdH: I was in 1999 in France during the total solar eclipse and that made a big impression on me. For me that is still something very high on my wish list. I really hope to be able to attend the eclipse in 2017 in the U.S., or else the 2026 eclipse in Spain. I think an eclipse is really one of the most beautiful things that you can see in your life, and advise everybody to try to see at least one total eclipse in their life.