First experience with astrophotography

Halema'uma'u eruption and stars (Sony A7 35/2.8 Zeiss)

One of the great things about shooting with a camera like the Sony A7 that has an advanced sensor is that you can shoot astrophotographs with less noise that ever before. This comes into play with the inevitably long exposures you encounter when shooting the night sky. On a recent trip to view Kilauea volcano as we’ve done many times, I wondered if it might be possible to capture both the volcano and the star-filled sky in the same shot; so I began to research a bit on astrophotography. I’m by no means an expert; but I’ve learned a bit.

Equipment

I shot with a Sony A7 full-frame mirrorless camera. It’s got an excellent low noise sensor. At least [one reviewer] prefers the A7S because it’s larger pixel size allows this A7S’s sensor to capture more startlight. The published images do look amazing. I shot with a variety of lenses during my limited experience on Kilauea. Most of the images that I captured were shot with a wide angle, either the Zeiss/Sony 35/2.8 or a Voigtländer 15 mm Leica M-mount with a Metabones adapter. The wider the aperture, the better because it enables shorter exposures at lower ISO settings.

A tripod is essential for the long exposures used in astrophotography. I use a Gitzo Basalt tripod. It’s a little bulky if you’re planning on hiking a distance with it; but it solid and stable. I’ve taken it out on long hikes out to the active lava flows and it’s withstood a lot of abuse. You’ll want a proper head for the camera mount. I love the equipment from Really Right Stuff. It’s pricey; but their products are beautifully made and engineered to perfection. On top of the Gitzo, I use their BH-40 ballhead. Just so you know, you will need an Arca-Swiss bracket for the camera. On the A7, I was tempted to buy the Really Right Stuff bracket; but I opted for a well-made less expensive option this time around.

How I found this spot

We stayed one night at the historic Volcano House overlooking Halema’uma’u Crater. Since there’s a lava lake occupying a portion of the crater floor, I expected to see some nice incandescent glow after dark. Right on schedule, after sun began to fall, the glow became visible about a mile in the distance. But almost at the same time, as the sun slipped behind Mauna Loa, the temperatures began to fall and with the high dew points, clouds formed instantly in the cool air, nearly completely obscuring any views of crater. I packed up my gear and went to bed.

I woke up again at 1 AM to my alarm, peered outside and saw clear views of the glowing vent; so I packed my equipment and started hiking about a mile down to the steam vents. I ended up taking the wrong trail in the complete blackness; and while backtracking, the clouds and fog rolled in again. This time, visibility was reduced to a few feet. I eventually made it back to the room and slept another hour. At that point, I began consulting the Hawaii Volcanos Observatory webcams. I figured that if they were showing clear views of the vent, then I should be able to drive down to a point close enough to walk, fire off a few shots before the fog came in again. Sure enough, around 2:30 AM, I caught a glimpse of the vent looking sharp on the webcam. Again, I grabbed my gear and sped off in the Jeep. After about a 300 yard walk, I found a spot with a beautiful view of the glowing gasses. Every now and then you could catch the sound of the lava rumbling in the crater. It was a spectacular experience. Since the stars were out, my goal was to capture both the star field and the crater. So many of the photos were taken with the Voigtländer 15 mm Leica M-mount lens. It’s a so-so lens overall; but it certainly gave some nice sweeping views.

Halema’uma’u eruption and stars (Sony A7 15 mm ISO 6400, 15s

Process

To capture the stars, you have to dial up the sensitivity. I bracketed for ISO settings. Most of the shots were taken at ISO 3200 or 6400. I chose not to use the Auto ISO setting out of concern that the algorithms might choose to ramp up up the sensitivity beyond the point where noise would limit the quality too greatly. Most of the images were shot wide-open to minimize the exposure length. Exposures are going to be several seconds long. With exposures that are very long, one risks star trails. Because the earth is rotating, the light from the stars will inscribe an arc on the image if the shutter is open too long. There is a heuristic for computing the maximum shutter opening duration as a function of the focal length of the lens. The so-called “Rule of 600” states that the maximum open shutter duration is 600 divided by the focal length of the lens.[1] An experienced astrophotographer posted his web calculator at the Lonely Speck. With either the rule of thumb or the more sophisticated calculator, it’s just a starting point.

Focusing is difficult. You must use only manual focus. Since you are photographing objects that you may not be able to see with the naked eye, it is hard to focus in the same way you may be accustomed to normally. I would start by moving the focus ring to infinity, then trying to identify the brightest star to fine tune your focus on.

Since I didn’t have a remote release, I just used the timer function on the camera to delay the activation of the shutter. Since the exposures are so long, I’m not even sure how necessary that it.

Conclusions

It’s not difficult; but noise is an issue. Some of the images are noisier than I’d like. I’m anxious to try the Rokinon 24mm f/1.4 ED AS UMC[2] and see if I can get the exposure times down a bit more.


  1. You can read a detailed discussion about the Rule of 600 here

  2. This is a big bulky lens; but the author of the Lonely Speck regards it as ideal for astrophotography. You can read his review.