Technical Insight - Making a Cress Time-lapse.

Time-lapse films have always fascinated me. Watching something unfold that I couldnít see in realtime captivates me. Itís a view of the World I know happens but canít be a part of without recording it and speeding up, reducing hours, days, weeks or months in to minutes.

Having never made anything like this before I wanted to see if I could make an interesting time-lapse film and thereís nothing that teaches me better than actually doing, so I set myself a little challenge of making one. I decided on growing some Cress from seed on a paper towel because the entire growth process is visible. As you'll know most seeds are planted in soil so we don't get to see the germination process. With Cress, it doesn't care that it's sitting on top of some damp paper. As long as it's moist, it's good to go. I'd have loved to film a starry sky passing overhead in some deserted landscape but the beauty of filming the Cress meant I could do it at home. The Milky Way will be a project for the future.

What is a time-lapse?
Simply, a time-lapse is a sequence of images capturing an event which is then speeded up to show something happening over a much shorter time than happens in reality. To apply that to our example Cress growing sequence, it took eight days for the Cress to grow to maturity from seed and we see it played back in 30 seconds.

Not all time-lapse sequences are recorded over this length of time, some are shorter, a sunset over a city for instance would be recorded in an hour or so and some sequences take much longer to record, like erecting a building, which can take months.

The simple set for the cress time-lapse The Set
I used quite a simple set. A white background with an infinity curve and placed the paper towel with the seeds at the front of the set. See the diagram to get an idea of the layout. I wanted the background to be almost white so I lit that and used reflectors next to the camera to catch light from the background to brighten the Cress.

After getting the general set up right, there was some fine tuning to get the camera in just the right spot. I had to predict where the Cress would grow so a little guesswork was required. I angled the camera to capture both the seeds as they started the growth process and hoped that this angle was sufficient to include the Cress as it grew to itís full height. I didn't want the Cress to grow up and out of the top of the frame as that would have ruined the effect. I think I got the guesswork right.

A time-lapse is a sequence of images so I set up the camera accordingly. Although the finished product is a film, it starts out as photographs. Remember too that the photographs have to be transposed in to frames that work with popular video sizes so I had to ensure my images were of the right size and that I framed the scene so I could crop later without losing any of the plant. I knew I wanted to finish up with a full-HD film so each frame had to be at least 1920px wide and 1080px high. As long as the images were in excess of that, I could resize them later to fit the video size.

Each exposure was f22 @ 2.5 sec. This was the smallest aperture I could use with my 50mm lens. This meant I was using the largest depth-of-field (DOF) available to me. However as I was using an extension tube, the DOF is reduced considerably so I had to make use of every millimetre offered by that F22 aperture.

I wanted the best quality image possible so I set a very low ISO, 100. Because the camera was on a tripod I knew the shutter speed could be quite long, it was 2.5 seconds in the end. As part of setting up I was able to shoot some test shots to get the exposure spot on.

It took eight days for the Cress to grow from seed to full height. An image was taken every 12 minutes. In total there were 960 individual images.

There is quite a bit of kit required to shoot this particular timelapse so lets run through what I used.

Camera Ė Any camera will do but it must offer certain functions critical to capturing a successful time-lapse so lets take a look at those features.
1. Remote release port
This lets you plug in a programmable release accessory called an intervalometer. See below for an explanation of why this is critical to the process. Some cameras may have one built-in so it's worth checking before heading out to by one.
2.Tripod mount
The camera must maintain itís position for the entire time it's recording the event so it had to be mounted on a solid platform like a tripod. Of course you could just leave the camera to freely stand on a table top and as long as it doesnít move then its fine but it only takes a small movement to ruin the effect which also ruins days of recording.
3.Manual exposure
The time-lapse sequence needs to use the same exposure setting throughout so by setting it manually you know it cannot change. Itís important though to ensure that the lighting is consistent too. Each frame should be lit exactly as all other frames.
Because I was shooting close up to the Cress to fill the frame, I also needed the ability to use a lens with an extension tube which shortens the closest focus distance considerably. I used a 50mm lens fitted with a 13mm extension. This actually made the stable base even more of a necessity as any movement at this close-focus distance would be very obvious. 5d
This was my camera for the shoot. It met with all of the required criteria I described above but other makes and models are available!

image of an intervalometer Intervalometer - This is an accessory that plugs in to the camera and fires the shutter at pre-determined times. Itís configured by the photographer who decides the interval required between shots and sets this device accordingly. Without this thereís no time-lapse! Itís important that the camera has a port that the Intervalometer can plug into. Mine fits in to the remote socket on the side, In the same place you would fit a external shutter release, for that is all an intervalometer is, a remote release thatís programmable by the photographer. The model I used is the Yongnuo MC-36b.

Before starting the sequence ensure thereís enough juice in the battery, if they run out the device will stop working and the unbroken sequence will be lost.

Tripod Ė Keeping that camera steady for days means this has to be a rock-solid platform for your camera.

Lights Ė For my setup, the light came only from artificial lighting Iíd set up. I think they were the small fluorescent bulb types. As these lights have a different colour temperature to daylight I ensured I took a frame with a grey card to get an accurate white balance for post-processing.

A dark room Ė I found a space that I could put up my little set and leave undisturbed for a week whilst I block out the light completely. This meant covering up a window with a purpose-made light blocking material. With no natural light creeping in, I knew my exposure was going to match only the output of the artificial lights I put up around the set.

The recording of the images is just the first part of the time-lapse process. After all the images have been created it's back to the computer to turn them in to a short film. Remember I intended to make the final film in full HD, so 1920x1080. This means I have to resize those 960 images in to the right size and crop. Doing that individually would take FOREVER but the photo editor I use, Corel's PaintshopPro, has a script feature which allowed me to program a routine to resize all of those full-size images automatically. This took an hour or so to complete but it's a lot easier to watch it processing than it is for me to resize each image. If I wanted to do any additional processing, like sharpening, colour-balance or adjusting exposure I could just as easilty set up another script to process the batch to do all of that automatically too. The editor might have taken the original oversized images and cropped them to fit the HD dimensions, but by cropping them in my script, I had complete control over how they were cropped.

So that's the images prepared. The next step is to start the video editor and import them. After import there was a little trial and error as I determined what was the best time I should leave each image on the screen. I can't remember exactly what this was but it was something like 1/10th second. One of the next decisions is to decide the frames-per-second (FPS) of the final film. For this I chose 30 FPS. The film would then be about 30 seconds long. I had little idea how this would turn out or how smoothly the Cress would grow. Watching it now it's a beautifully smooth progression from seed to fully-grown Cress. I didn't have to make any further exposure adjustments as these had been done by the photo processing so all that was left was to begin the final render. I don't know what the exact relationship is between the time the frame is on screen and the FPS rate but the settings I chose worked first time so I didn't do any further testing.

Lessons Learnt
It was quite nerve-wracking to make this as it's so easy for things to go wrong throughout. Keeping everything in the same place, keeping the Cress watered, ensuring the lighting was consistent and not letting the batteries expire was a challenge. I did have to change the batteries in the camera so I was pleased that it was locked in place on the tripod and the battery compartment was accessible whilst it was mounted there. Perhaps having a mains power plugged in instead of batteries might have helped here. Also ensure the memory card is big enough to record all of the images. I was left with more questions too as I learnt about the editing process. I have some experimentation to do in the future. If you haven't watched it already, the final film is available at the top of the page.

Further Reading.

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