Thursday, May 5, 2011

Part 2: Time-lapse Photography - Photography with Imre - Episode 36

I couldn't be happier with how the time-lapse episode turned out. There's a lot of information in this show and I also have a few new and expanded details to add in this post. Don't forget to check out the Web Resources section below as well, because there are some really cool and awe inspiring time-lapse flicks to watch, amongst other cool sites to explore on the topic.

Intervalometers
In my video I talked a little about intervalometers and the ability to purchase "devices" that can be hooked up to the camera. More specifically, these are essentially "smart" remote cable releases that can be setup to take shots at particular time intervals. Some manufacturers make their own and there are a variety of third party ones available too; click here to see what's on Amazon for example. Since I haven't used any of these, I cannot recommend any models so be sure to do your own research on them.

Many DSLRs can also be tethered to a computer and controlled via software. Again, some manufacturers have an intervalometer feature in their programs, while in other cases you can purchase third party packages. There is a also a third option for the code savvy DIY-ers out there, which is to download a software development toolkit (SDK) from the manufacturer (if available) and program one yourself. I recently downloaded the Olympus SDK and if time permits, I'll be trying my hand at it.

Choosing a Time Interval
The time interval chosen will essentially set the pace for the time-lapse movie. In addition, depending on how long you planned your movie to be, the time interval might also determine how long a period is required to shoot the series of photographs. For example, if one chooses a slow pace for the movie with time intervals spanning two seconds and a movie length of 10 seconds, then at 30 frames per second (fps) one will need a total of 300 frames, so the time-lapse series will take a mere 10 minutes to shoot. On the other hand, let's say you want a time-lapse movie of the sun crossing the sky from rise to set in 10 seconds playback time. Well already you know that'll take a half of a full day to shoot, but let's do the math. Assuming that on this particular day the sun is "up" for 12 hours, here's what we need to know:
  • We already know that a 10 second long movie played back at 30 fps requires 300 frames
  • In 12 hours there 720 minutes (12 * 60 = 720)
  • We can divide the number of minutes by frames to get time interval needed for this shoot. Thus, 720 / 300 = 2.4 minutes between shoots or 144 seconds (or 2 minutes and 24 seconds); that's 25 photos in an hour
One hopes that if you're shooting something this long you can leave the camera safely alone to do it's work, otherwise you might be in for a busy day! Anyway... I'm sure you get the idea in regard to working out how many frames you need; quite simple math really.

But what isn't that simple to determine necessarily is to get the right look for the subject you're shooting. This is why I deliberately varied the time intervals during the city skyline time-lapse movie seen in the show. By doing so, the apparent speed things move at depending on the interval used became fairly visible. For example, at 15 second intervals the clouds drifted noticeably faster across the sky than at 5 or 2.5 seconds. But in my opinion, the subject alone doesn't solely dictate what time span(s) should be used between exposures, because one also has to consider the audience for the video and in many cases the creative aspect. Maybe a producer wants to use a quick time-lapse clip between action scenes in a short film to denote a hectic, frantic pace or feeling of excitement. On the other hand, a short time interval will result in smoother motion and could present a calming or peaceful effect; can also show more detail since things are moving so quickly in a scene. My ultimate suggestion here is to watch many time-lapse movies made by others and see what it invokes you in and then start shooting various subjects to see what you get and like.

Acceleration and Deceleration
I certainly haven't come across many time-lapse videos that use acceleration or deceleration, in other words, most I have seen use a constant time interval between each exposure throughout the whole movie. But nonetheless, when I have come upon it, the effect is quite cool.

Basically there are two major ways to achieve this, one easy, and the other being a bit more involved. The easy method is simply to shoot a time-lapse series with a constant interval and then speed up or slow down the resulting movie in a video editor. That's it. Or there's the more challenging method of varying the time intervals as time passes. Now a question does pop up. Does it make sense to bother varying the time intervals when you can do this without much fuss in an editor? Well perhaps some producers might feel that varying the time intervals keeps the movie "real", while others might believe that it's more cost/time effective to use software. Whatever the case, here's my view which you might find interesting.

If I were to accelerate a portion of a time-lapse movie then I would use a video editor. But for slowing things down to a crawl I would actually shorten the time intervals during shooting. Here's why. When you accelerate a video clip, the software basically drops frames in order to accomplish the effect. Another way of seeing this is that the visual difference between each consecutive frame becomes greater, thus motion will appear faster. If I was shooting a time-lapse series and making time intervals longer between each exposure to speed up the action, the end result will basically be identical because the difference between each consecutive image will be greater just as if the video were to be sped up using an editor. Essentially, I can save some time and effort by using the editor to get the same result.

On the other hand, if you've ever tried to slow down video using an editor, the motion generally becomes choppy or somewhat unnatural even with frame blending or other filters that are supposed to smooth out motion in such cases. This effect occurs because frames are reproduced multiple times in order to get that slow motion look. So to get natural and gradual decrease in speed, I would instead rely on reducing the time interval during the time-lapse shoot. This way, no frames would need to be doubled, tripled or whatever to get a reduction in speed.

The bad part about this is that it requires some planning before the shoot and potentially manual operation. Please correct me if I'm wrong, but I don't know of any intervalometers that can gradually increase or decrease intervals --although for us programming folk, we could tether the cam to a computer and write software to accomplish such a thing. But anyway, this may not be as bad as it sounds and here's a few steps you can follow:
  • Consider how long you want the deceleration to last. Let's use 3 seconds as an example; at 30 fps that would equal 90 frames.
  • This effect usually looks better if it's more in-your-face than subtle, so hopefully the time intervals you're starting with are fairly long. To continue this example, I'll start with 15 second gaps.
  • The next thing to consider is the time interval you are ending with. Let's say... 1 second.
  • In this particular example, we're dropping 14 seconds off our time (15 - 1 = 14 easy). I take the total number of frames, 90 and divide it by 14 which equals 6.4 that I will simply round to 6 to make life easier.
  • What that means is that every 6 frames there will be a 1 second decrease in the time interval between shots. So the interval between frames 1-6 will be 15 seconds, 7-14 will be 14 sec., 15-22 will be 13 sec. ... and so on until you reach frame 90.
This might keep you a bit occupied for a while, but the end result should be a fairly gradual decrease in speed when the movie played back.

Tracking (Moving the Camera During Shooting)
In the show I briefly discussed tracking, a sidewards motion of the camera, and if you check the Web Resources section below you'll find plenty of links to professional and DIY time-lapse dollies and tracks (along with some pretty wicked videos that were created using them; some cinematography terminology links too). You'll probably notice that the videos tend to look more interesting if there are foreground elements fairly close to the camera, as those objects tend to create a stronger sense of depth and motion in the scene; perhaps keep that in mind if you're creating such footage. Maybe someday when I have more time I'll look into either building one of these units myself or getting one if it's not too expensive. And by the way, I'm not affiliated with any manufacturers mentioned here; their websites are posted for further research and information.

Putting it All Together
You might have noticed that I kept the part about putting a time-lapse movie together quite short in the video. If I was to present my version of how to do it, then I would be using Adobe After Effects or Premiere; those employing other packages would have to figure it out on their own anyway... which in my opinion is not very hard. With After Effects and Premiere, all you basically do is import the photos as an image sequence and then drag the clip to wherever you'd like it in the timeline. Then to add some pizazz to the footage one can start applying various other effects like color grading and vignetting or whatever else. Applying those effects are easy... it's using them wisely and creatively that can be more challenging.

I hope you have a lot of fun creating and watching your time-lapse movies. I certainly found a few surprises which I couldn't see when taking the shots, like those construction elevators running up and down the sides of skyscrapers being built and the motion of the crane on top of the building. I have no clue what to do for the next episode and not because I don't have any ideas, but too many! So perhaps I'll put it out to a vote on Facebook. L8r!

Web Resources
http://www.youtube.com/watch?v=d1japIhKU9I - Great video on various filmmaking techniques

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