Pixean
Nov 26, 2018

Time lapse videos depict an entire event in a much shorter duration of time. They are played at great speed and hence enthral the viewers. Time lapse photography takes a lot of practice to attain perfection. There are kits dedicated to this genre of photography. They may not be mandatory but they go a long way in helping you achieve excellence. There are a few other nuances involved in this that not many are aware of. We don’t think of these while we are getting ready for the shoot and this becomes a major headache when we are at the location. These include concepts like frames per second and time intervals. A little bit of mathematics is also involved. So it’s time for you and your grey cells to get together…

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Image courtesy: Londolozi Blog

Frames per second: This is actually a term related to video editing and filmmaking. A frame is actually the smallest entity of a video. FPS or frames per second determines at what rate the video is being played. The standard is 24 fps or 25 fps. In case we want slow motion videos, we shoot in 60 frames per second and then playback the video in 24 frames per second. Time lapse videos are captured at very low frame rates and then sped up to the standard 24 or 25 fps. Here is one simple way to understand a frame of a video. Import any video into a video editing tool, for example Adobe Premier Pro. Introduce the video to the editing window and pause it. Navigate through the video using the navigating keys on your keyboard. You will find that you are actually navigating one frame at a time. If your current sequence is set at 25 frames per second, you will have to press the key 25 times to actually get through 1 second of the video. Hence each time you are pressing the key you are actually moving ahead by one frame. 25 times you perform the movement, and you are ahead by 1 second.

Time interval and the duration of shoot: Time lapse photography requires an intervalometer. This is nothing but a digital timer capable of controlling the number of shots your camera needs to take and the interval between each of the shots. This normally doubles up as a remote shutter release cable as well which is a great advantage. Before you go out for the shoot, you need to have an idea of the duration of the shoot. If it is an event, you will know the duration from the client or the organiser. In case of natural events like sunsets etc., a sky chart or a sunrise-sunset calculator can come in handy. This will help you determine the time interval i.e. the interval of time between each shot. This calculation has to be precise since the standard display format is going to be around 24 or 25 fps or even 30 fps. Let us get down to some mathematics to actually analyse the process of determining the time interval for your shoot.

The math behind it:

Suppose you are shooting a time lapse video of a dance show. You need to approach the organisers for the duration of the event. Let’s assume that the event is two hours long. You need to determine the duration of your video. This normally depends on a bit of market research since you need to sell your video as well. A 30 second time lapse can be a good option for a 2 hour long event. Think of the playback speed of your video too. The standard options are 24 or 25 fps. You may even want to use the 30 fps option.

Let us calculate the desired number of frames. In the above example you chose to shoot a 30 second video and playback the video later in 24 fps. This gives you a total of 30 multiplied by 24 equals 720 frames.

The desired duration of the video in seconds ( 30 ) X the desired playback frame rate in post-production (24 fps)  = the total number of frames to be shot ( 720 ).

Coming to the next phase of our calculations, calculate the duration of the event in seconds. For the 2 hour long event you are going to shoot, converting it into seconds gives us a total of 2 multiplied by 60 (for minutes) and then further multiplied by 60 again (for seconds). This gives us a total of 7200 seconds.

The total duration of the event in seconds = number of hours (2) X 60 (minutes) X 60 (seconds). Total duration = 7200 seconds.

We have already reached the final part of our calculations.

The actual time interval will be the total duration divided by the desired number of shots.

Total duration of the event in seconds (7200) / desired number of frames (720) = the interval of time between each shot (10).

Hence it’s simple. You want to shoot a 2 hour long event in a 30 second video and play back at 24 frames per second. For this you will require a time interval of 10 seconds which means that each shot will be taken 10 seconds after the previous one.

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Image courtesy: muvee

How it can go haywire: Without this simple calculation you can go haywire while shooting your time lapse. For example in the above scenario, you choose to take a shot every second which is the common go-to when we are lazy. In this case, your video will become 10 times longer. What should have been a 30 second video becomes a 5 minute video, thus rendering it almost useless.

 

Time lapse photography is a unique combination of photography and a bit of mathematics. This makes things interesting as well as tricky. However, if you spent some time getting through this blog, I am sure the calculations seem a lot simpler now. I am also sure you are ready for your next time lapse!