I have an opportunity to do some shooting for a friend, they are asking to get some time lapse photography as they build a small tower. They want to be able to condense one days worth of construction into a short video for presentations, I did not see an area for this in the forums but thought that it may be a good idea for the community for people to be able to share their experiences, tips & tricks, and best practices for advanced techniques!
In order to accomplish a nice film we must consider a few things, after safety and area of operation considerations, that are present with the drone. The number one limitation you will run into in this case is the flight time, flights of 20-30 minutes will allow you to capture 20-30 minutes of time and lapse it by changing the frame rate at which it is captured (more on this in a second). One way to deal with this is to utilize multiple batteries and to "reload" the drone as needed. The nice thing here is depending on your time interval and total length of filming, you can keep the drone airborne and when you change out a battery, you wont really mess with the overall flow much, since there is a lot of time between consecutive photos, and a few missing will not kill the end result.
There is a second option that will work in a pinch, but is not technically time-Lapse as the product at the end varies slightly in its visual properties. You could instead of taking photos at fixed intervals; take a video of the 20-30 minutes and speed it up at play back. This will condense time (taking a half hour and making it play back in 30 seconds) however since you are filming at 24 -30 FPS, you will get an ultra-smooth, albeit very fast playback of the same video.
There are a few factors we must consider when setting up for our Time- Lapse shoot (with respect to the time lapse, you still need to consider safety, and lighting and all of that; but we will stay focused on the time lapse here).
1) Total Time to Film (domain)
This is the entire length of the shoot start to finish, first picture to last. If you want to catch a sunrise it may be half an hour, if you want to catch the building of a house it may be multiple consecutive days of four or more hours, or even a few stills from the same locations over 30 days.
2) Time interval Between Shots
This is the time between taking the next consecutive shot, it is related to the frame-rate or more aptly the amount of time compression (lapse) that we wish to accomplish. For example, if you take a photo every 10 seconds of a process that takes 1000 seconds total you will end up with a video that takes 100 seconds when finished (playing at essentially 10x speed, this does not figure in frame rate yet).
3) Total Number of Photos Taken
This is the total number of photos required to shoot at the set time interval for the time Domain you wish to cover.
4) Total Time of End Product
How long will the finished video be?
5) Frame- Rate of the Final Product
What will the final product play at 24 FPS, 29.97 FPS, 30 FPS ?
Now that we have these factors defined lets see how to use them and why they are important:
Lets use an example: We will use a sunset as our example. We will aim for a 2 hour window to catch both before, during, and after (remember to always shoot through your shots!). We want to end up with a 60 second movie (@ 24 FPS) of the time lapse sunset. With this information we can determine the settings we will need to utilize, as well as how many batteries this would take to do continuously.
One thing i will say is getting everything in terms of the same unit will help us out a lot here, in this case most of our things will be in seconds (time interval) so lets convert 2 hours into the equivalent number of seconds...
Time in Hours * 3600 = Time in Seconds
( 60 mins per hour, and 60 seconds per minute = 3600 seconds per hour) in case you want to know where 3600 came from)
2 Hours * 3600 = 7200 seconds Total Time
Next, we want to think about the end, this is always good practice, what do we want to get out of this? We said we wanted to end up with a 60 second clip for our final product. Using this and the frame rate for our final video we can figure out how many photos to take total.
Final Product Length * Frame-rate (FPS) = Total Shots Taken
60 seconds * 24 frames per second = 1440 total shots needed for end product.
Now we can determine the interval needed to squeeze exactly 1440 shots into our 2 hour window. To Do this we must take the total time and divide it by the total number of shots we need.
Total Time / Total Shots Taken = Time Interval (seconds)
7200 s / 1440 shots = 5 Seconds per shot
it should be noted this is actually going to cause an issue since the DJI App now only allows at minimum a ten second interval times since a recent update... App developers out there?! But for our purposes we will ignore this limiting factor, i will discuss how we plan to circumvent this later.
Ok, so we now have figured out, the time interval, the total number of shots and for our purposes we will look at one last thing, the Time Compression Factor, that is to say how much will this video be essentially condensing or lapsing time.
Total Time of Shooting / Total time of End Video = time Compression Factor
7200 s / 60 s = 120x
This tells me that our video is 1/120 of the original time (actual time event was recorded over), in other words we should be seeing the video at about 120 times the rate it was actually occurring. This is neither here nor there but may be interesting to know.
Lastly, if we want to know the number of batteries we take a safe estimate of 20 min flight time, over the 120 min we must fly...
total time (min) / est. time per flight (min) = total number of charges (or batteries)
120 min / 20 min per flight = 6 charges (batteries)
[Always be conservative here, more power is infinitely better than running out]
So, In review we will have to set our time interval to shoot every 5 seconds, for a 60 second video playing at 24 FPS, which will condense 2 hours of real time (by a factor of 120)!
Now for the practical, due to limitations of the 10 second per a shot minimum on the DJI APP, we have elected to utilize a two prong approach. First, we will utilize a NIKON D5100 DSLR on a tripod to shoot the entirety of our little project from a fixed position, this will give us time lapse from the entire day. Second we have decided to utilize the Phantom 3 to capture augmented time lapse from the aerial perspective. That is, we will fly for the 20-30 minutes focusing on "Details" of the construction, since we know we will have one camera devoted to the entire project we can think of our drone footage as spice added to our video. Allowing us to use the drone to capture interesting events and angles, that will supplement the main Time Lapse From the Nikon camera, This should provide us with a more interesting final product as we can cut between time lapse of the entire project, and time lapse of details provided by the drone. PS... Triple check your batteries are fully charged!