Time Lapse Photography

Source

A couple of years ago my son wanted to do a photography project for school. We had recently bought a Canon EOS 550D DSLR, which he was keen to use. While wasting time browsing various photography sites, I found several references to using the Canon for making time lapse films. The basic concept is that you take a sequence of still photos over several hours and then combine them together into a video format. Thus you can condense many hours of still photography into a short video, which shows a speeded up version of the scene you photographed.

Equipment.

Certain types of photography are well suited to making time lapses. Astro-photography and landscapes are a couple of obvious candidates. Apart from a suitable camera, you need a few additional bits of equipment:

  • A decent tripod. The camera must not move between shots and will need to be in the same spot for as long as the time lapse lasts. This can vary from a couple of hours to a whole 24hrs, or more.
  • An intervalometer (see below). Not essential, but makes life much easier.
  • A lot of patience. You can be standing around for hours in the cold and initially you will probably experience many frustrating failures.

Battery Life.

If you are going for a long sequence consider getting an extended battery pack. If the temperature is low your battery life will be considerably reduced. You might want to try warming your battery pack, but this can also cause condensation on the lens!

Intervalometers.

You can trigger the shutter of a Canon either from a PC via its usb port, or by using something like a RaspberryPi. See:

However, for outside work this is very inconvenient and prone to failure. It's far better to use an intervalometer. The basic functions are:

  • Delay: the amount of time between pressing "Start" and when the first picture is taken.
  • Interval: the time between which photos are taken. If you set this to one minute a photo will be taken every minute.
  • Long: The amount of time the shutter is left open.
  • Number: the number of photos you want the intervalometer to take.

There are a lot of these around. Here is an example on Amazon. They all seems to be made in the same Chinese factory. Try Googling "Hongdak MC-36B". The cost is £10 upwards depending on who you buy it from. If you are serious about time lapse photos buying one of these will save you endless hours of frustration. Note different models support different cameras. Make sure you buy the right one for your camera! There is a good review of the Hongdak here.

Alternatives to Using a DSLR.

Note that neither the Pi, nor the GoPro are suitable to taking photos of stars, although the rumoured GpPro4 is meant to fix that problem.

Raspberry Pi.

Definitely a geek solution. Relatively cheap when bought with a camera.

  • There are a couple of dedicated cases suitable for outdoor use, but a real geek will use a Tupperware box.
  • You can use a rechargeable battery and its low power consumption means it will continue working for a long period.
  • Camera is surprisingly good, but definitely not up to DSLR standards.

Disadvantages:

  • If you are working outside there is no easy method of getting a preview of what the camera can see. It's possible to bodge this by making the Pi into a WiFi hotspot and using your phone to view the photos it has taken. However, not very practical, except for the real hard core geek.

GoPro.

Why use a GoPro?

  • It's very light. Important if you are carrying it up a big mountain.
  • It comes in a waterproof case, so you can safely leave it outside without worrying about it getting soaked.
  • There are innumerable fixings and brackets available. You can easily attach it to something like a walking pole as a tripod.
  • If you get fed up of time lapses you can use it to film your wing suit jump.
  • It has reasonably comprehensive time lapse facilities built in.
  • Controllable from your smart phone or via a WiFi dongle.

Some disadvantages:

  • Short battery life. Around 2hrs in optimal conditions, although you can get extended battery packs.
  • Not suitable for photographing stars, although general low light performance is good.
  • Limited exposure control and a fixed wide angle lens.

Night Time Photography (Stars and Star Trails).

The factors to consider are the ISO setting and length of exposure. If you set the ISO too high, the camera sensor will produce a lot of noise and degrade the image. If you set the exposure to be too long, the stars will move while the photograph is being exposed, leading to blurred images.

Make sure you turn auto-focus off. The infinity setting on your lens is probably not going to give you a sharp image. Make sure you focus manually. I tend to use an aperture of around F5.6, but this will depend on your lens. Generally using your lens's widest aperture won't give you the best results.

Set your white balance to around 3500K. This helps to reduce redness from any sodium lighting that is around and will give you a blue sky. If you leave your shutter open to log, you will get star trails, as the stars move across the sky during the exposure because of the earth's rotation. To avoid star trails limit your exposure to 1000/focal length.

If you want to capture star trails, take multiple exposures over a few hours. You can the "stack" the multiple images to produce trails. There are several applications for Linux:

If you are in the northern hemisphere you will get the best trail effect by pointing your camera towards the north. The pole start appears fixed in position, so if your camera is pointing towards it the stars will form trails centred around the pole star.

You may also want to take a dark frame. Simply put a lens cap on and take a photograph using the same settings you use for taking the star trails. You can use the dark frame later on as a method of removing background noise from your photographs.

Landscapes.

I live in the countryside and am a keen mountaineer, so have lots of opportunities for landscape photography. One of the key requirements is to identify suitable spots to take time lapses in advance. Sunrise/sunsets are a good place to start. However, you need to know where the sun will be when it sets/rises and be in the right location to record the event. Usually a clear view of the horizon, or some definitive feature e.g. a mountain.

Often success/failure will depend on the weather. The best landscape conditions are often in the clear atmospheres of autumn, winter and spring, when haze is minimal. Some clouds in the sky add interest, as they will move during the period of your filming. Be prepared for frequent disappointments. Often cloud will be too extensive, or the mist will descend at an inconvenient moment.

It's particularly important to let your equipment equilibrate to the ambient temperature. If you don't do this you will almost certainly get condensation on the lens, which will ruin all your efforts. Allow around 30 mins for the temperature of the camera to equilibrate. Sometimes there is so much humidity that you will get condensation anyway. This can often happen when it's cold.

Software.

So you have had a successful filming expedition and now have hundreds of JPG's you want to convert into a Hollywood Epic. There are many tools available, but I use ffmpeg and mencoder.

ffmpeg is correctly known as the Swiss army knife of video manipulation. It is in perpetual beta, the command line options get changed on the developer's whim and it can probably even make the tea. There are a whole raft of video conversion options. I freely admit that I don't understand most of them, but I'll try and explain why I chose the ones I use.

First you need to check that your JPG's are numbered sequentially. If they aren't I'll leave you to write a script that renames them. In the case of the GoPro file names look like: G0040383. Now ffmpeg has a very useful option: startnumber that will start at the file you name and process all the files in the directory with sequential numbers. However, if there is a gap in the numbers it will grind to a halt. Even better ffmpeg understands shell globs, so: 

ffmpeg -f image2 -start_number 91495 -i G00%d.JPG

will process all the files in the directory that start with "G00" beginning with "G0091495".

Almost all of my ffmpeg options are taken from waan's site.

So my full command line looks like: 

ffmpeg -f image2 -start_number 91495 -i G00%d.JPG  -r 25 -s 1280x960 -vcodec libx264 -b:v 30000k timelapse_25fps.mp4

This creates a video of 25 frames per second using an h264 codec. If your time lapse seems to be going too quickly, you can adjust the speed using mencoder: 

mencoder -speed 0.25 -ofps 25 -ovc copy timelapse_25fps.mp4 -o quarter_speed.mp4

The above command will slow things down to a quarter of the original speed.

So now you have the perfect time lapse video and you want to spice it up by adding an audio track. I am assuming that you already have a suitable mp3 to hand. There will almost inevitably be a mismatch in the duration of the mp3 file and the video. If the mp3 is too long you can trim it to the length of the video when you multiplex the file: 

ffmpeg -i timelapse.mp4 -i music.mp3 -map 0:0 -map 1:0 -codec copy  -shortest output_video.mp4

If the mp3 file is too short you can create a loop that is longer than the video (thanks to StackExchange for this): 

sox -e ima-adpcm short_audio.mp3 looped_audio.mp3 repeat 1000 # adjust count as necessary

Now use the shortest option with ffmpeg to multiplex the tracks, as per the instructions above.

Some of My Time Lapse Videos.

I have uploaded several time lapses to YouTube. These are all quite short and only intended to show you the sort of effects you can achieve:

  • Cwm Eigiau sunrise from the slopes of Carnedd Llewelyn.
  • Sunset taken with the Canon DSLR.
  • Sunset taken using a GoPro.
  • Stars time lapse taken using the Canon DSLR.
  • Dawn to dusk time lapse taken using a Raspberry Pi.