These days, there are few things in life that I am willing to stay up all night for. One of those things happens to be a view of the center of our Milky Way galaxy floating above Mt. Rainier.
Joe and I had only gotten minimal sleep the night before, but the forecast and time of year were perfect for it. I spent nearly two days trying to determine where we should go to see the Milky Way, before settling on the towering mountain. My choice of location was Sunrise on the northeast side. The center of the galaxy, being located roughly between the constellations of Sagittarius and Scorpius, hugs the south-southwestern horizon, meaning that from Sunrise, we would see the galaxy appearing directly above the mountain.
Before setting out, I loaded up on as much information as I could about how to properly photograph the Milky Way. I now know why the picture I attempted to take on our backpacking trip failed so miserably:
- I wasn’t taking a picture of the center of the Milky Way. The center of the galaxy is the brightest and most complex. Other parts are visible, but not nearly as remarkable (or photogenic) as the center.
- My exposure was actually too long. Originally, I thought it was too short at 30 seconds, but when I inspected it more closely, 30 seconds at 18mm focal length was definitely too long; long enough that the stars visibly moved, creating trails and making them look blurry and oblong.
- My ISO was way too low. I’m used to the line of thinking that you should keep the ISO low, because it can really introduce a lot of noise into a photo. This does not apply to astrophotography, however. The ISO needs to be really, really high to compensate for the fact that the exposure is limited by the focal length of the lens.
So, this is how I went about photographing it this time around:
- I set my exposures between 15 and 20 seconds, to avoid visible movement of the stars. The formula that I’ve seen for calculating maximum exposure for a cropped image sensor is 300/focal length. Obviously, this means that the shorter your focal length, the longer your exposure can be. I was shooting at 18mm, which I gather is generally considered a bit long for shooting the Milky Way, but it’s the shortest lens I have, so I took 300/18=16.667 seconds. Hence, my exposures started out at 15 seconds and I took some at 20 seconds, just to see if I could get away with it.
- I kept the aperture at f/3.5. Shooting as wide open as your lens allows is necessary to let in maximum light.
- I cranked the hell out of the ISO, taking it all the way up to 3200. I actually didn’t even know the 30D could go that high, but I found it buried deep in a settings menu and enabled it.
- I found a really dark spot. Theoretically, if there was no light pollution, I should be able to see the center of the galaxy from my living room window. But thanks to the blinding lights of Seattle and its surrounding suburbs, all I can see is a golden glow against the sky and maybe a couple of remarkably bright stars/planets. Finding a place where light pollution is a minimum is obviously a must. A great tool for finding dark skies is the Dark Sky Finder. You want to aim for places that are colored blue or black as these tend to have the least light pollution.
- I went during the summer months, when the center of the galaxy is visible.
- I made sure I had a good view to the south, as that is where the center of the galaxy is visible.
- There was no moon in the sky while I was photographing. The moon is an incredible source of light. Moonlight will definitely affect the visibility of the galaxy dramatically.
- Focus to infinity. This is the part that I struggled with the most last night. My lens doesn’t let you know when it’s focused to infinity, so out of nearly 180 pictures I took last night, there are only a handful that are in focus. I recommend you get your focus right during the daytime and then don’t touch it once you’re out shooting.
- And finally, post-processing seems to be where the magic really happens. I shot all of my pictures in RAW, so I’d have the highest quality files to work with. Noise is certainly an issue with astrophotography because the ISO is so high, so the majority of my post-processing went to reducing noise. A great technique is to apply a reduce noise filter and selectively reveal it via an inverted mask in Photoshop. Here is a tutorial for doing that.
Here’s my EXIF data for the pictures that turned out the best:
Exposure: 20 seconds
Focal Length: 18mm
As a bonus, the Perseid meteors were in full swing last night, and I managed to get a shot of the galaxy with a couple of meteors flying through the sky. Also, if you look closely, you can see the headlamps of a couple of climbers on the mountain.
Eventually, I’d like to get a shorter lens so that I can take some longer exposures and in turn lower the ISO so there’s less noise, but overall, I’m really happy with what I was able to get last night.