Cristian Berges: Night sky time lapse movies

A deep blue sky with red and orange clouds running over it, getting darker and darker – until finally, the stars appear and draw their circles.

That’s what you get if you are lucky – a night sky time lapse movie reveals the movement of the earth, it becomes perceptible.

This example movie has been shot in step motion with a DSLR camera. The sequence of pictures was processed into a film by Quicktime Pro with no further post production or retouching. The quality has been reduced due to compression.

• Equipment:
• Camera: Canon EOS 550D
• Lens: Sigma 18-200mm 1:3.5-6.3
• Timer: Meike MK-550DL
• Tripod: Manfrotto 501 HDV

You don’t need to be a professional cameraman or utilize expensive equipment to create such a movie. All it takes is:

• a DSLR camera with a tripod, no film function necessary
• a reasonably fast lens
• an interval timer
• Apple’s Quicktime Pro software

1. Setting up the camera

a) Exposure at night time

If you start shooting your time lapse movie when it’s already dark and the stars have come out, set your camera to manual mode. Concerning the exposure, you’ll need to gather some experience. Here’s a suggestion for your first attempt:

• open your lens’ aperture as far as possible, let’s assume it’s a 2.8
• set the camera’s sensitivity to ISO 200
• (any higher value might cause many ‘hot pixels’)
• set the shutter speed to 30 seconds.
• set the interval timer for your camera to 31 seconds

Please note: The exposure time doesn’t only control the exposure, it also determines the speed of the stars’ movement in your final film! If you are able to reduce the shutter speed because you have a faster aperture, you can also shorten the interval. As a result of this, the stars will move slower in your final film. Do some tests to decide what interval/ speed you prefer (within the limitations of your equipment).

Your exposure time shouldn’t exceed 30 seconds. Otherwise, the moving stars will appear as stripes instead of points on each single photo. Anyway, most cameras are restricted to  30 seconds as their longest shutter speed before they switch to bulb mode.

I’m shooting with a Canon EOS 550D. In my experience, it’s problematic to use any ISO value higher than 200. Due to the long exposure time, a high number of ‘hot pixels’ will show up.

The small red and blue dots are ‘hot pixels’. They are practically inevitable at long exposure times.

b) Exposure for day-night transitions

 It is a nice effect to start your time lapse recording before it gets dark. Your film will show the transition from the last daylight (with a spectacular sunset – if you are lucky) to the appearance of the stars.

In this case, you’ll have to cover a broad range of changing brightness – too much contrast range to use your camera’s manual mode with a fixed exposure.

In my experience, the best choice is to go to AV mode, where you can set the aperture while the camera adds the appropriate shutter speed for each single shot. Since shutter speed offers finer gradations for controlling the exposure, AV mode is better than TV mode.

To minimize the danger of unsteady exposure and the flickering effect it may cause in your final film, you should set the metering mode to evaluative metering. This includes the average brightness of the sky.

Also try a correction factor of at least -1 aperture to maintain the dimmed light  of the the evening sky. Otherwise, it may look like bright daylight.

c) white balance

Set your camera’s white balance to the daylight preset. In my experience, this offers the best color reproduction for the blue evening sky, red clouds, the dark night sky and – if available – tungsten lit objects in the foreground.

d) resolution

Of course, you’ll get footage of optimal quality when you set your camera to maximum resolution and RAW mode. But if you prefer quicker results and less data volume, choose JPEG mode with best quality and a resolution just slightly above full HD, which is 1920 x 1080 pixels.

e) power

The creation of a timelapse movie  may take at least two hours. Since your camera will be under constant demands during this time, you’ll need a high-capacity and fully charged battery. To reduce energy consumption, it makes sense to deactivate the display.

f) tripod

Since you want to capture the smooth movement of the stars, your camera has to be completely fixed. The slightest shift will destroy the result. Because of this, it is vital to use a good and solid tripod. And – of course – to carefully avoid any collision during the shooting process.

g) image stabilizer

If your lens or your camera has a built-in image stabilizer, you should deactivate it. Otherwise you may get blurrings due to the incalculable activities it performs during the long exposure times.

h) focus

It’s important to set the focus manually. This is extremely difficult when it’s already dark. You won’t see the tiny stars through your viewfinder or on the video display screen. The best solution is to set the focus in time – before it gets dark.

i) framing

The proportion of your DSLR’s images will probably differ from the 16:9 aspect ratio of the movie you want to create. When you do the framing, it helps to keep in mind that  the result will be  more ‘narrow’: A certain area on the upper and on the lower part of the picture will be cropped away.

2. The right location

It depends on your visual intentions: If you prefer a ‘puristic’ time lapse movie which shows only the sky without any foreground, you can shoot almost everywhere: Out of your window, on your balcony or on an open field. Just make sure that there will be no light sources radiating  into your lens.

You’ll probably find the clearest night sky out on the countryside. On the other hand, the slight gleaming over a big city – caused by the diffuse reflection of it’s lights – may add an attractive background brightness… instead of having pure black.

To reinforce the impression of the moving stars, it can be interesting to have something in the foreground. Since you are shooting a time lapse movie, two criteria are vital. Your foreground should be:

a) completely static and immobile

b) constantly unlit

Houses, for example, are a good foreground – because they don’t move. However, trees can be problematic as long as it is not completely windless.

Even minimal movement of branches, twigs and leaves will lead to a nervous, vibrating flickering in the final movie. This draws the attention away from your main subject: the smooth movement of the stars.

Since you will be working with extremely long exposure times up to 30 seconds, your foreground objects have to be unlit – as constantly as possible. To avoid an overexposure, you should be looking for a dark location with no lights around. A street lamp, for example, would cause too much brightness, even if it’s not in the frame but just lighting the front of a building from a distance.

Also try to avoid light changes. The shorter they appear, the more disturbing they are. Above all, cars driving by are a no-go: When you are shooting with an interval of 30 seconds, their light may be captured in just one or two individual photos. In the final movie, the resulting effect is an irritating flash, lasting just the fraction of a second.

While you can avoid the presence of cars and similar light sources by choosing a remote and lonesome environment, another problem remains: The light traces caused by planes flying by. Because of their speed, they also appear for no more than one or two images in your sequence.

You can see this effect in the movie above at seconds 6/7 in the lower right corner, and at second 10 in the middle of the picture.

If you want to get rid of these ‘blotches’ on the night sky, your only chance is to use the retouching tool of a software like Photoshop.

3. Patience

It takes some time to shoot a night sky time lapse movie. Here is how to calculate it:

film length (seconds) * frame rate * interval (seconds)/ 60 = minutes of shooting

For example, when you are shooting with an interval of 30 seconds and want to create a movie with a length of 10 seconds at a frame rate of 25fps, you’ll spend 125 minutes on location.

4. Making the movie

The easiest way to create a movie from your sequence of pictures is to use Apple’s Quicktime Pro Software. You can download the Quicktime player for free. Then, for approx. $ 30, you can upgrade it to the Pro version.

The process is quite simple: After you have stored all the pictures of your night sky time lapse sequence in a folder containing nothing else, you open the Quicktime Pro software.

In the ‘file’ menu you find the ‘open image sequence’ option. Just choose the first photo of your sequence and the frame rate (25 fps in europe), and Quicktime does the rest.

You can now play the movie and judge the result. To export it as a movie file, open the ‘file’ menu again and choose the ‘export’ option.

Now you have various options as to file format and codec. If you want a movie with standard 16:9 HD proportion, click on ‘size’, then choose ‘HD 1920×1080 16:9′ and activate the ‘keep aspect ratio’ button with the ‘crop’ option.

Download here the video

© 2011 Christian Berges