How to time-lapse Part IV
- Category: Blog Filming and Video
- Published: Wednesday, 30 July 2014 12:47
What are time-lapses?
Practical thoughts on the time-lapse technique - Part IV
Time lapsing step-by-step
In this part I will talk about some preliminary considerations and production.
Iceland has become a popular destination since the singer Björk made her island famous by her songs. Yet few people know Iceland during wintertime. And I am sure that they miss a beautiful part of the island: the snow covered rocks, the magic arctic light and especially the phantastic aurora borealis dancing in the sky. The days spent at the Jokülsarlon glacial lake were one of the most beautiful and peaceful Christmas time I remember.
Before I start to rig up my camera on location I quickly go through following questions, which help me to set up the time-lapse correctly:
- What do I want to capture? It helps a lot to spend some thought on the choice of the motive. Unlike the situations of normal photographing or filming in real time, when time lapsing the picture frame will alter in the next half an hour. What changes in the picture and what remains the same? As by my lapses I want to demonstrate a shift in time obviously I will look for motives that will change its shape or position. The passing clouds, the wandering shadows or the spinning stars in the night sky may deliver impressing effects.
For more depth in the picture I choose a photogenic object in the foreground that does not change over the time. I avoid elements in the photo that move fast in real time, like branches or leaves in the wind. Also birds or animals may cause aliens in the sequence if they appear only in one or two images and than disappear. I soften the fast movements of the waves or the flow of the water by choosing a low shutter-speed. For that I use a strong gray filter (ND Filters) to lower the light intensity.
- At what time of the day do I take the sequence? When I started my first experiences with a DSLR I chose that times of the day when I could expect a constant light. That is after sunrise. Later I tried to work also during the night. Night shots were more complex also because I couldn’t distinguish much on the camera display, especially if the stars were really sharp. The autofocus would reach its limits so I had to take test photos and step by step reach thus the desired focus. But in both situations during the day and night the shutter-speed and the ISO don’t have to change its initial value. I will talk later about the aperture and white balance. In case there are fast moving clouds, which may alter the light conditions very quickly it is best to go with shorter intervals between the shots to avoid the so-called staccato effect (later in the finished video clip you may get light and shadows jumping annoyingly around the scene). The most difficult time-lapses are those that begin during daylight and end with a starry night sky or the other way around. That is why these types are called the “Holy Grail”.
In these situations the initial set-up values of the camera change during the sequence. Either the camera changes these settings automatically (in the automatic modus) or a third-party software alters the ISO and shutter parameters at certain paces during the transition from day to night. This is called bulb ramping. I found that both methods are quite unreliable and may destroy the time-lapse. Of course it was very convenient for me to let the camera run in automatic modus and wait until the night falls. But there are serious disadvantages:
- First, the automatic exposure reaches its limits when the first stars start to shine and the whole picture sinks into a black soup.
- Second, the camera automatic tries to adjust the aperture. But in case of a DSLR this doesn’t happen infinitely variable but it’s controlled mechanically and produces slight differences in the apertures of the photos. This leads to a light flicker in the sequences that is almost impossible to remove in the post-production. You may watch a very good example of how the mechanical control of the diaphragm works and how it leads to slight differences in its diameter from one picture to the next:
- Third, the camera adapts the automatic white balance to the present light temperature, which becomes colder when the sun has set. That also causes an unpleasant flicker in the sequence and it is very difficult to erase it in post. As to the bulb ramping method, the software cannot always identify correctly how fast the light changes considering that the twilight duration differs from the latitude or that clouds may influence the light conditions.
Thus the safest way to go is the manual method. I adjust the shutter speed and than the ISO manually as soon as the dynamic limit of the camera is reached (that is when the photo would be over or under exposed.) Of course there is always the risk that the intervals between two shots are too sort and I mistakenly turn the wheel into the wrong direction in my hurry. Or that I hit the camera in the dark (and here I have to mention that even the faintest light source could destroy your painfully taken time-lapse so get used to work in the dark). But this is when my little assistant comes into play. The CamRanger is a little device mounted on the cold shoe that I connect with the Canon by a cable. It sends the captured pictures including the histogram to my IPad by Wi-Fi so I can control the exposure. And the best is that I can adjust various parameters, like the ISO, aperture, focus, shutter speed, live-view, time-lapse intervals etc. just by tapping on my IPad screen – without touching my camera. It makes it possible to adjust the values during a Holy Grail even when it is dark. And if it is too cold outside I may hide in the car and watch the camera from inside. When the picture gets too under (or over) exposed I adjust it for one or two f-stops to gain again a correct exposure by changing first the shutter speed (until I reach the time limit given by the intervals) and than by changing the ISO. I can level the generated leaps in the exposure later on in the post-production phase by a software program called LRTimelapse.
How long should the time-lapse run? If you plan to deal with this subject you need first of all a lot of time and a lot of patience. To shoot something quickly won’t function with time-lapses. It takes at least a quarter of an hour just to look for a motive, to make considerations and to set-up your camera, including to make some test shots. The actual length of the sequence capture depends on three factors:
- The interval between two shots depending upon the situation. Generally I choose:
- one to five seconds for quickly moving clouds (like the cotton-wool clouds), people running through the frame, cars or objects fast passing by (like when taking photos from a car). An interval of a minimum of two seconds ensures enough buffer time for the camera to write the raw data on the card (In this case I prefer to use my Panasonic GM1 who uses a smaller raw data size and controls electronically the aperture and shutter. Thus I can choose shorter intervals and avoid the flicker.)
− ten seconds for sunsets or cirrus clouds
- ten to twenty seconds for wandering shadows, spinning stars at full moon and for a very active aurora borealis
− twenty to thirty seconds for hardly perceptible movements, for a high standing sun, for a weak and diffuse aurora borealis or for the stars when the night is very dark (but shutter speeds above twenty seconds may lead to star trails – however an interesting effect if desired)
− two minutes for fast growing plants or opening blossoms.
These intervals are valid for wide-angle lenses. For tele-lenses shorter intervals may be more appropriate.
2. The number of the taken photos: although the cards have significantly dropped in price for the last years, I still have to be economical with the available memory, especially on my longer trips. From my experience I know that I need around five to six hundred photos for a Holy Grail sequence. So if I plan to do several sequences of this kind, like on my trip to southwest of USA, I try to limit the other sequences to two hundred fifty or three hundred photos per time-lapse (that gives me a video clip of ten to twelve seconds at a 25 fps). For example, if I want to capture the night sky I would need approximately one hour to have enough pictures that show distinctly the moving of the star in the later clip. That means that for three hundred pictures in sixty minutes I choose an interval of twelve seconds (if there is a full moon a shutter speed of ten seconds at a high ISO would suffice). These clips will render a playing time of twelve seconds at a framerate of 25 fps.
3. The desired length of the video clip and the intended frames per second (in Europe it will be a rate of 25 fps, in USA 30 fps. For a more cinematic look you may choose also 24fps): in general a clip should have at least an eight second length within a timeline. But to leave more space for transitions in the editing process I calculate a minimum of ten seconds playing time for the later clip. Going for a 25 fps rate it makes it easier for me to count quickly how many pictures I need to take.
JPEG or raw? If you intend to take time-lapses just for fun to show them to your friends on YouTube and if you don’t want to invest too much in your time and memory space than choose JPEG as the capturing format of your photos. But you have to take certain limitations into account, like a baked-in look. The raw format allows capturing even in difficult situations with high contrast or hardly available light. I can edit the lows and the highs much better in the post-production and secondary adjustments won’t deliver unaesthetic artifacts. If I use the CamRanger device for the transitions from day to night I even take raw and small JPEG together. The small JPEGs are delivered to my IPad where I can quickly judge by looking at the histogram if the parameters are still within the desired range.
Which focal length? Before starting my trip I consider which situations I may encounter on my trip and on what type of pictures I want to focus. Based on that I will select only the necessary equipment in order to travel light. If I plan to capture more landscape photos than I will probably not use a heavy tele-lens. Therefore I pack better two super wide-angle lenses (a 14mm and a fast 24mm/f1.4 for night shots). If I am hunting the aurora borealis I add also a fish eye lens to cover as much as possible the sky.
Manual or automatic settings? For best results I recommend a manual setting of the camera. The only situation when I would use a time automatic (Av modus) is for a sunset time-lapse when the light is changing fast (and I am too lazy). With the Av modus the aperture, the ISO and the white balance is fixed. In case you choose a spot light metering be sure that no alien object (like a bird, car, cloud etc.) passes through that spot. This may lead to a sudden change of exposure in one picture and possibly destroy your sequence. That is why I prefer the centered integral metering. To avoid a light flickering the aperture should always have a fixed value that does not change during the time-lapse. The best is to use a manual lens which aperture is not controlled by the camera. Or, if you have an automatic lens, choose the open aperture. During daylight you may adjust the shutter speed by a ND filter. What if you don’t have a filter? Or if you take a transition from day to night? (You cannot unscrew quickly the filter from the lens when the night falls) And no manual lens available? Than there is another trick: the unscrewing of the lens. First I focus as desired, set the needed aperture and than I press and hold the DOF button to set the diaphragm, unlock the lens with the other hand and rotate the lens slightly until the camera will show a zero value for the aperture. The lens is still connected to the camera and set at the desired aperture but it is electronically disconnected from the camera. But beware! Don’t forget to fix the lens back when your time-lapse is finished! I always switch for manual focus to be on the safe side. If you set the aperture at any other value than open the camera will close and open the diaphragm at the set value every time it takes a picture but with small deviations. This is one reason why flicker or strobes in the time-lapse occur. As to the white balance I choose also a fixed setting. In case of raw picture it doesn’t matter if it is set for clouds, sun or at a certain Kelvin value as I can adjust the white balance in the post. In case of JPEGs you should always set the correct white balance but you will have a problem if the light temperature changes during a sunset. So that is another reason to pick the raw format. Even if I go for the time automatic at sunset I fix the ISO otherwise the camera will try first to raise the ISO before adjusting the shutter speed. This produces unnecessary noise in the pictures. When considering the shutter speed for a time-lapse you must take into account the so-called 180-degree shutter rule. A short exposure captures only little of the action in the scene and leads to staccato effects. Besides, fast shutter speeds (higher than 1/100 second) lead to flicker in the clip. By dragging the shutter you add a certain motion blur that looks more naturally to the human eye.
- Which part of the picture should stay in focus? When doing a night time-lapse I am often confronted with the focusing issue if I have an object in the foreground. In order to keep the stars and the foreground object in focus I can either step back some meters (at the cost of the perspective) or I can choose the hyper focal distance. Thus I focus between the fore- and background and close the aperture that much to just get both in the depth of field. On my trip to the southwest of USA I wanted to capture a Holy Grail time-lapse with two bizarre rocks in the foreground. Because I wanted to add some loftiness to the relatively small rocks I wanted a low-angle perspective with the camera positioned near to the rocks. At the time of the set-up there were no stars yet and I had a shallow depth of field due to the open aperture. If I would have focused on the rock edges I could foresee that the stars at the far distance would see like sludgy white spots. I could focus at an indefinite distance and go for the stars but I would have got blurred rocks and destroy the sunset part. The only solution I found was the focusing at the hyper focal distance.
In another situation I captured a time-lapse with the camera moving on the slider along a weird-winged rock at night. Again the slider was very close to the rock due to the perspective but I had to choose between the sharp stars or a sharp rock. Because of the parallax shift and the amazing 3D effect of the foreground I went for the sharp rock and accepted the blurry stars.
In the next blog, the last part of these how-to time-lapse series, I will write about the post-production and how to get a nice video out of your hard work on-site.
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