21 Jan Time-lapse photography – Part I
Time-lapse photography is the process of compressing time by taking a sequence of images with a delay between each image, and then stringing those images together to create a movie. Clouds appearing to fly across the sky while the sun rises and sets in a matter of moments is the most commonly seen example of time-lapse, often used in cinema to give an impression of a large period of time passing.
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Pretty much scene that has some sort of change over time can make a pleasing subject for a time-lapse sequence, and when starting out, the simpler the better. Pointing your camera out a window at the world outside is how most people start out, and there’s much to be said for it.
The technical benefit is that you have complete repeatability while you experiment and learn, and the practical benefit is that you can go about your daily business while the camera does the work. Standing beside your camera while it clicks away for an hour or more is not the most exciting way to spend time on location 🙂
The Bare Minimum
So, what is the absolute bare minimum of equipment you need to get started? A camera is a necessity of course, and depending on what camera you happen to have, that may be all you need at first. Some cameras already have built in time-lapse functionality built-in, so you don’t have to buy any extra kit.
Some compact digital cameras have this functionality, but most SLRs do not. Considering how much more the SLRs cost, it’s a strange omission, unless you’re a camera manufacturer that wants to sell ridiculously expensive accessories 🙂
In most situations, you are also going to need a tripod, to keep your camera steady and keep it at the right angle to capture the action. As for lenses, there is no special requirement, your choice of lens depends totally on the field of view and depth of field you want to capture.
If you have a compact digital camera that doesn’t have time-lapse built-in, then you’re probably stuck, as you don’t even have the option of buying those expensive accessories. With an SLR, the accessory you need is called an Intervalometer, which basically gives you the ability to shoot at “intervals”, hence the name.
Chinese versions of the intervalometer are much cheaper than the official brand versions, and are readily available on eBay and elsewhere. They plug in to the accessory socket of your SLR, and allow you to choose how many shots you want to take, the time delay between each shot, plus a few more features like taking multiple exposures.
If you happen to have a Canon Digital SLR, then you have a fantastic (and free) alternative to buying an intervalometer. It’s a piece of software called Magic Lantern that you install on your camera. It gives enhanced functionality over the vanilla software that comes installed on the Canon, and one of those features is an intervalometer.
How long of a delay to I need to leave between each shot?
It really depends on how much movement there is in the scene, how smooth you want your final video to be, and how much time you want to compress down. For example, when shooting moving clouds, on a windy day you might need an image every 3 seconds, while on a still day, 10 or even 15 seconds would do fine. Likewise, if you are taking a sequence to track progress on a construction site, one picture every day might be all you need.
How many shots do I need to take?
This depends on how long you want your final video to be. For example, if your final video is going to run at 30 frames per second (fps) and you want the final video to be a minute long, then you need 60 x 30 = 1800 frames. If you are taking one image every 5 seconds, then to get your final minute of footage, you are going to be keeping your camera company for 1800 x 5 = 9000 seconds, which is two and a half hours, so bring a book 🙂
How do I expose for changes in lighting over the sequence?
If you are shooting a sunset (or sunrise) then the amount of light is going to change pretty drastically as time passes. It isn’t possible to lock in an exposure that will suit both extremes. What you have to do is pick an exposure that works at least with the most challenging part of the sequence. For example, when shooting a sunrise, you’re going to be trying to guess your exposure when it’s dark.
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Obviously if you go by the camera’s meter, it’s going to want to take really long exposures, which is not what you want. You need to choose an exposure that suits the interesting part of the sunrise, which is when the sky starts to brighten. Under-exposing somewhat will enhance the colours of the brightening sky, so you have a bit of leeway. The correct exposure to use will come with experience, and will depend on how cloudy it is, and where the sun is in your composition.
To recap, you need to choose a manual exposure to suit the most interesting part of the event, not what happens to be in front of your camera when you start.
HDR stands for High Dynamic Range, and it involves combining several images at different exposure levels into one image. It can create a very surreal effect if over done, but if used correctly it will give a beautiful image that shows correctly exposed areas where one shot would have had blown highlights or lost shadow detail.
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HDR can also be used as part of a timelapse sequence, to create a sense of hyper-realism and capture every detail. You need to take into account the extra time it will take the camera to shoot and process the extra images, so you might need to increase the delay between shots.
SLRs have an exposure bracketing function that allows you to choose the exposure range, normally with just 3 settings, underexposed, correctly exposed and overexposed. Three images isn’t ideal, five would be better, but most cameras don’t have that option. However, the Magic lantern software for Canon D-SLRs allows for up to 9 photos to be taken. That said, when doing a timelapse with hundreds of images, 3 shots is probably plenty, considering the wear on your camera’s shutter.
The example below is from the Photomatix user gallery, and shows a shot that would be impossible without combining images to create HDR. The photographer exposed for the outside view through the window, then the interior, and finally a medium exposure. They were then combined to create the image shown, which has correct exposure across the entire frame.
Adobe Photoshop had a HDR importer that will create a composite image, but it seldom works well, and it’s not practical when dealing with thousands of images in a timelapse. There’s a piece of software called Photmatix that has a myriad of HDR options and will automatically deal with a timelapse sequence.
It’s always a good idea when shooting a timelapse with moving foreground to introduce a small amount of blur, by increasing the exposure duration beyond what the camera meter advises. The point of this is to make a more natural looking video, as we expect to see blur when objects move.
We can exaggerate this effect to create more artistic effects, for example light trails from moving cars, and streaks for moving people, just by increasing the exposure duration. Water can also be turned into mist by increasing the exposure duration.
Before you start shooting, there are a few things you need to do for a successful time-lapse, and for your convenience, these are listed below, and I’ll explain each shortly. Depending on your camera, not all of these options might be available.
- Set White balance to a specific setting (not Auto)
- Choose Manual mode
- Turn off Autofocus
- Choose an appropriate resolution
- Use a memory card with enough capacity
- Use fully charged batteries
- Don’t touch the camera!
1. Set White balance to a specific setting (not Auto)
If you leave this setting at Auto, the camera may change the white balance during your sequence, which will cause colour changes.
2. Choose Manual mode
Any other mode may result in images in your sequence having different exposure settings, as the camera adjusts to changing light conditions. You don’t want this as it will cause a very noticeable flickering effect in your video.
3. Turn off Autofocus
If you leave this on, the camera may hunt for focus and fail to take any picture at all, especially likely if you are shooting at dusk or dawn. The camera may also choose to focus on a completely different part of the picture than you intended, such as a passer-by walking across the frame.
4. Use a memory card with enough capacity
You don’t want run out of room on the card before the sequence is finished. See item 7!
5. Choose an appropriate resolution
Though your camera may shoot a gazillion pixels, it may be more practical to reduce resolution to something closer to your final video. This will cut down on processing later on. I’ll discuss the post process in the follow-up article. There are other reasons to shoot at full resolution, which I’ll talk about later.
6. Use fully charged batteries
If you’re taking hundreds or even thousands of photographs, you don’t want to run out of juice half-way through. Even better would be a grip which attaches to your camera and allows you to use two batteries at once. As with the intervalometer, there are chinese variants of these which are much cheaper than the official option. To help prolong battery life, turn off the lcd if possible.
7. Don’t touch the camera!
There’s nothing worse than waiting patiently for your camera to to shoot hundreds of images, then waiting hours for your computer to process them, only to find you kicked the tripod during the shoot and the sequence is ruined. Trust me, it sucks.
And there you go, if you’re new to timelapses, then practice and experimentation are your friends. I hope this introduction has been useful, and perhaps you’ll come back for part 2, where I’ll talk about the bit after the shoot, when you process all those images and turn them into a wonderful movie 🙂