The other night I went to the roof just before sunset on a really hot, muggy late July evening in New York. When its this hot and humid, you get amazing sunsets as the thick air cuts the glare from the setting sun. I setup my camera to shoot a time-lapse of the sun setting over New Jersey. Once the camera started going, I was distracted by one of my neighbors who was up there with his brand new bulldog puppy. Below is a frame from the time-lapse.
The sun over a hazy New Jersey (click to enlarge)
I almost didn't post this as it didn't come out very well. The camera was set in full manual mode (manual focus, manual shutter, manual aperture), was shooting "FINE" JPG photos, once every 3 seconds for a total of 765 frames. At 24 frames per second, this would yield about 30 seconds of video. I've done this many times, so nothing new about this setup and execution, except for the subject matter - a setting sun.
If you watch the video, you'll immediately notice a rather annoying flicker to the video. It would seem the camera's exposure was varying slightly on each frame. If you read the metadata on each still photo, its apparent that the camera's settings were in fact the same on each photo. So what causes the annoying flicker?
It turns out that despite it being a marvel of electronics, a Digital Single Lens Reflex (DSLR) camera is still mostly a mechanical camera. It has a mechanical aperture ring, a mechanical shutter curtain and a mechanical mirror that flips out of the way to expose the sensor to the lens. In particularly challenging lighting conditions, such as a sunset, very minor differences in this mechanical execution can result in subtle changes in exposure that when put in sequence, turn out quite glaring.
You can get around this by doing a few things I didn't yet know about. Firstly, you should open your aperture as wide as the lens will go. On this lens, a wide angle, that would have been around 3.5 yet I had this camera set at f11. Opening the aperture that wide would over-expose the photo, especially at the start of the sequence when the sun is higher, but you can compensate with a faster shutter or dialing down the exposure compensation. Opening the aperture fully locks the ring in that position, removing on the more influential variables in getting a consistent exposure.
Secondly, despite capturing far more data than needed to produce an HD video, you should shoot in RAW. Normally I shoot RAW all the time, but for time-lapse, because you're taking so many photos, space on the memory card is a premium. On my camera, a RAW image is 21 megabytes. In JPG mode, its about 12 megabytes. If you do shoot RAW, most photo editing software can use a plug-in that will analyze each photo's exposure curve and mathematically smooth the transition from light to dark across the entire series of frames, thus avoiding the jerky shutter. Surprisingly, that software is free but since I didn't shoot RAW, I couldn't use it.
I will chalk this one up to lesson learned and will try again. In the meantime, here's a photo of that bulldog puppy.
The dog days of summer (Instagram photo, click to enlarge)