Night Skies and Time Lapses

I think we all have a photography-list of things to do and try. Making photos of the night sky and creating a time lapse movie was on mine for a while now, and with the longer daylight hours of summer it’s rather comfortable to give these a try: have dinner at home, drive out in the evening, find a good location while there’s still some daylight left, and then spend a couple of hours outside, in the night.

I drove out and up to Laguna Mountains, and hiked to the upper part of Laguna Meadows from the Penny Pines trailhead. Since I was quite early, I continued to the Sunset Trail and found this lovely little meadow – you can see how the treetops are illuminated by the last direct sunlight from the west (I’m looking mostly east in this photo).

Twilight pastel colors on a silent meadow along the Sunset Trail, Laguna Mountains, California. July 2011.
Twilight pastel colors on a silent meadow along the Sunset Trail, Laguna Mountains, California. July 2011.

After sunset, it was time to return to the spot I had picked for my nighttime photos, at the upper end of Laguna Meadows, north of Big Laguna, the largest of the three bodies of water up there. The word “laguna” is Spanish and means lake – both Big Laguna and Water of the Woods are more or less reservoirs or ranch ponds where the water is held back by earthen dams. Little Laguna is a natural lake as far as I can see, but it only fills up after very wet winters. But I digress. Back to the night photos!

The sky still had a faint blue hue about 50 minutes after sunset (a time that falls within nautical twilight), and as it was getting darker the Milky Way appeared right above Laguna Meadows:

The Milky Way above Laguna Meadows, Laguna Mountains, California.
The Milky Way above Laguna Meadows, Laguna Mountains, California. Nikon D700, 15s @ ISO 3200; f/4, 16 mm

I found that these stills are actually fairly easy. I used a wide angle lens because I wanted to have a lot of sky in the frame. Using a wide angle lens also has the advantage that exposure times of 15, maybe 20 seconds are relatively safe.

Exposure Times

So why not use longer exposure times? Because the Earth rotates quite fast, actually! You don’t see this movement with your own eyes, but with a longer exposure time, the stars will turn from dots to streaks. That might be a desirable effect in really long exposures, to produce “star trails”, but for photos that show good definition of the Milky Way, it’s not desirable.

For the longest time, the “600 rule” was supposedly a good standard to keep the stars from turning into streaks. You take the number 600, divide it by your focal length, and the result gives you the maximum time you can expose without getting motion blur of the stars. For a 50mm lens, this would be 600/50 = 12 seconds. From my personal experience, that’s too long already. I have some 10 seconds exposures, made with a 50mm lens and they already show motion blur. I’d make that a “400 rule” to be absolutely safe.

Also, remember the crop factor of your camera when you use that rule. With a 50mm on a DX sensor Nikon, it’ll be like “600/(50*1.5)” = 8 seconds. (or with the “safe” approach of a “400 rule”, just 5.3 seconds)

So the real problem is capturing enough of the faint star light and Milky Way within the maximum exposure time frame – and my f/4 wide angle zoom (the 16-35mm VR Nikkor) is probably a bit slow for that. The above photo was made while there was still some light left in the sky (hence ISO 3200 was okay), but for subsequent shots I had to raise the ISO to 6400, which of course introduces quite some amount of noise in the darker areas. Nikon’s 14-24mm/2.8 (for full frame) or Tokina’s 11-16mm/2.8 (for crop sensors) wide angle zooms are better lenses for that purpose – or an even faster prime lens.

Time Lapse Movie

With a single photo at a high sensitivity and relatively long exposure time, hot pixels are not that much of a problem, but things became quite different when I went for interval shooting to create a time lapse two nights later. Before I go into details, here’s the resulting movie – please “click through” to the Vimeo site, click on “HD”, switch to full screen, and depending on your screen size, turn the “scaling” option on or off:

Jeff Sullivan has just posted a nice general sum-up of creating time lapse movies on his blog so I just put down my observations from the night-sky time lapse making here.

  1. It’s important to know where exactly the “infinity” focus is for the lens. Most new “AF-S” type Nikon lenses don’t have a “hard stop” at infinity, they focus beyond infinity (Buzz Lightyear would like it, I guess) – which will turn the stars from bright little spots into tiny little discs. Looks bad, not advisable. I also want to stress that it’s important to check the focus twice – once when you set up the camera and frame the scene, and again just before you start the interval mode. It could happen that you accidentally touch the focus ring, and bam. I’m just saying. :P And bring a flashlight to check the distance scale of your lens in the dark.
  2. Operating mode of the camera. This should be manual for everything once you’re done setting up the camera. This includes exposure (time, aperture, ISO) and focus as well as the White Balance. It’s absolutely crucial to turn auto white balance OFF and set it manually. For a nice cool blue of the night sky, it’s advisable to set it to Tungsten, or Fluorescent, or somewhere in between (less of a problem when using raw data, but with the amount of data to expect, I chose JPEG – see below.)
  3. Make sure the battery is really fully charged, or even better, use an additional battery grip. A 2 hour interval with 5 photos per minute drained my what-I-thought-pretty-full (yes, my bad) battery completely. At that time, clouds had moved in on the scene so it was not too bad as I had to end the session anyway, but for really long time lapses it will be a show stopper – there’s just no way to swap the battery without changing the framing ever so lightly when the camera is on the tripod. Had I used long exposure noise reduction (see below) the battery would have been drained even faster I think.
  4. File format. I went for medium-sized JPEG files instead of raw data. After all, I wanted to create a relatively low-res movie out of the files. A medium-size JPEG of the D700 is still 6 megapixels (something like 3000×2000), in other words almost twice as high a vertical resolution as required for a “full HD” (1080p) movie.
  5. The interval time. From a TV documentary I had remembered that the guy was making one photo every 12 seconds. With my relatively slow wide angle lens, that meant I could make a 10 second exposure at ISO 6400 – but couldn’t use the long exposure noise reduction then. It turned out that one image every 12 seconds is too much, anyway. If I’d ever do that again, I’d probably go for one image every 20 seconds. Naturally, a long time-lapse movie will take even longer to create that way. On the other hand… the “majestic slow movement” of the night sky (the movie above runs at 20 frames per second) is a pretty nice feat of 5 images per minute.
  6. my tight interval timing and the lack of long exposure noise reduction of course caused a lot of hot pixels to appear. For the first time, I found out what the “sync” feature of Lightroom’s Develop module is good for. :) I simply went to the last image of the sequence, removed all the hot pixels, and synced the setting over the entire sequence. In the above video, I have removed the red and white hot pixels. If you look closely, you’ll still see quite some blue hot pixels – they are a bit harder to spot because they don’t stand out so much in the stills…
  7. One extremely annoying problem that I ran into where the slightly varying exposure times even while using the lens wide open. Every now and then, a couple of photos in the sequence would be about 1/3 of a stop darker than their neighboring frames. Everything was set to manual, so I have no explanation what might be causing that. Jeff’s article that I linked above mentions a plugin for Virtual Dub that can average the exposures. I created my time lapse movie with Google’s free Picasa (the “movie presentation” feature has a time-lapse mode that can create movies from 6 frames per second all the way up to 30 frames per second).


It’s not something I’ll want to do repeatedly. Working with the large sequence of photos, adjusting them, even with syncing settings in Lightroom, creating the movie… it’s rather time-consuming, and let’s be honest: there’s folks out there who make absolutely brilliant time-lapse movies, there’s no need for me to waste my time and try to play in that league. ;)

In the end… was it worth it? Oh yes. Being out in the dark at a location with little to no light pollution is an amazing experience all by itself. While the camera clicked along I was lying in grass, my head resting on my backpack, and simply gazed at the stars. After a while, the eyes adapt to the darkness, and it’s quite surprising how bright a moonless but clear night sky can be.

This article has been moved from my old photography blog to this site for archival reasons.

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