By E.M. Kinsman

Chapter 5:  Filming Clouds, The Sun, and In Severe Weather:  

    Clouds are beyond a doubt the most often filmed time-lapse subject.  I am always amazed when a client calls up requesting more time-lapse clouds.  Every possible cloud formation and weather situation has been filmed by the best cameramen in the world and this footage is readily available from the top stock houses.  Still the clients want  new - fresh footage, so several times a year I find myself out filming clouds.  Filming clouds has got to be one of the most enjoyable assignments a client can ever dish out.
    The most often requested clouds are the fair weather clouds associated with a cold front.  After the frontal system passes there is often a day a very nice clouds.  In the spring and fall the wind speeds can be quite high, but in the summer wind speeds associated with the clouds are about 15 MPH.  Relatively slow and nice. A good filming speed is 1 FPS.

    These same cloud types are often formed each day by evaporation on some tropical islands.  A favorite cloud photography area is each morning on the island of Hawaii.  As the sun heats the island nice clouds condense and evaporate.

    The requirements for cloud photography are relatively simple.  On a nice slow cloud moving day a filming rate of 1 to 2 fps is good.  Use a spot light meter to meter off the blue sky through a polarization filter - be sure to keep the polarization filter in the same orientation when it is placed on the cameras.  By metering off the blue the exposure will pull the blue to the correct exposure and leave the clouds over exposed by several stops so they come out nice and white.  The polarizer needs to be rotated for maximum contrast.
    Fast shutter speeds are desirable, but since clouds have no sharp edges, a slow shutter with a pile of neutral density filters will work fine.  The problem with a .5 sec exposure is - do you have enough ND filters to get the shot?
    Sun light is polarized by the dust in the atmosphere and has a maximum polarization ( and thus a maximum contrast) at an angle of 90 degrees to the light path.  This all means that at sunrise the sky to the North and South will have the highest contract.  his is the part of the sky where you would have the highest contract and the clouds would stand out the best - if this is really the part of the sky you are photographing is another matter depending on cloud patterns.  By the way - the 90 degree trick can be used to determine where the sun will rise before the sun comes above the horizon.  Want to blow a director of Photography's mind? use your polarizing sunglasses to determine the two maximum polarizations using a compass.  Take an angle of 90 degrees off a maximum toward the sun and you will have the compass heading where the sun will rise.
    Once a cloud shot is established, do not change timing rate - this will make a very obvious rate in speed of the clouds in the film and will result in an unusable clip.  Basic rules apply - never change a filming rate once a shot is established - trust your first instincts about the shot.
    One of the problems with cloud photography is the presence of airplane condensation trails can really mess up a nice cloud formation.  There are few ways to avoid the con trails in sky photography, other than picking a location where there are few airline routes.  In New York stare there are many contrails formed by jets leaving from NYC heading West.  The only saving grace of contrails is that the conditions for their formation are not grate after a cold front during the warmest part of the day.  The majority of my sunset time-lapse shots have at least a little contrail in them.  They can be digital removed with a little work if the sunset is great.

Sun Sets / Sun Rises

Video capture of a sunset ( Note distinctive CCD artifacts) NTSC signal fed into a frame grabber

    Optically there is no difference between a sunrise and a sunset.  There is a big difference weather wise - many summer clouds dissipate when the sky cools off and a nice cloudy day turns into a very dull sun drop shot .  A sun drop shot is when the sun basically drops to the horizon in a perfectly clear air.  This is considered the dullest sunset shot unless you are filming with very high focal length lenses and have a subject in mind for the sun to set in front of.  The most interesting shots are when the sun interacts with some sort of cloud formation.
    Photographic wise there is a big difference between sunrises and sunsets.  A bright sunset will always get darker in a well defined pattern.  A sunrise many or may not get brilliant colors depending on the placement of the clouds - thus you will probably not guess the correct exposure ahead of time.
    The shot below is of the above sunset with the video camera following the exposure - Note how the overall light intensity of the shot stays uniform - the sun started at F64 - 1/30 sec with 50 iso film and ended at F#5.6 .

    A sunset shot can always be converted to a sunrise shot by running the shot in reverse - although this is a bit ad-hock since many people will notice the clouds moving in reverse.  In the above shot it is hard to tell it is running in reverse.  I see this done all the time on national advertisements.

    If you are filming for the bright colors reflected off the clouds after sunset you will be interested in the following series of pictures.  The brightest colors take place about 20 min after the sun has set the horizon.  This spike of color only lasts 3 minutes, so a time-lapse shot targeted for the bright colors had better be filming at a rate compatible with the length of the desired footage.  I typically film sunsets with an exposure set for the bright colors - I use a 1/30 exposure set at F5.6 with 50 ISO film.  I usually film sunsets with an old Non-Rex Bolex ( no prism to create reflections) and film at a rate of one shot every 3 sec with a 16 mm lens.
    The different bight colors are reflected at different angles as the sun sets, so a bit of a wide angle is desirable. The animation below shows the desirable color change.  Each image is one minute apart.

Filming in Severe Weather Conditions: Very Cold Temperatures     Several years ago I was asked to photograph icicles growing. To do this the camera was placed outside in -20 degree F weather, wrapped with heating pads, an insulated blanket, and wired up to run. The only problem was getting icicles to form where they should. In this type of situation a Bolex camera which has not been lubricated with graphite will freeze up after about 300 frames. The newer Bolex non reflex cameras seemed to run a little longer. In a professional situation a special heated box is built for the camera. The whole idea is the camera is kept warm with an active heater and the lens films through a window.

If you are just filming sunrises and are worried about water condensing on the lens, a small electoral heater can be used. To increase portability and simplify things a chemical hand warming pack can be rubber banded to the side of the lens. To keep condensation of the lens only requires keeping the lens a few degrees above the dew point.

To film in severe rain, a water tight box needs to be built. Heaters are used to keep the camera a few degrees warmer than the dew point, and a rain rotor is used. A rain rotor is a spinning disc on a motor. The disk is out of 1/8 inch Plexiglas and can spin at a minimum speed of 300 rpm. Any water that hits the disc is spun off by centripetal force and any imperfections in the plastic are averaged out due to the speed of the disc. These types of systems are used on ships at sea so the pilot can see in the heaviest of rains.

Lightning strikes:

    The best way to film lighting strikes is with a special camera design.  (see chapter 1 ) Using a stepping motor controlled camera - a series of cameras I called my skycam series - I filmed about 8 lightning storms.  On one occasion lightning hit a tree about 20 feet from the camera, although the hit was not recorded the overhead strike was.  Typical apertures are around F#11 with ISO 50 film - with this exposure the strike will be over exposed but you will record the fine structure.  There are several nice texts written on lighting.

    The resulting footage is of scientific interest, but after many years in a stock house not a second has sold. The problem is the flashes are on a single frame and the footage looks strange.  There are a huge number of still photographers recording lightning strikes on a routine basis.  There are several companies that have a flash detector that will trip a camera in a few milliseconds.  Lightning strikes typically cone in pairs of two or three strikes that follow the same path with a duration of up to 300 milliseconds.  The flash trigger will trigger the camera on the first flash in time to record the second and third strikes.  These units sell for about $300 and are very nice to run in the daylight.  With an army of still photographers armed with this equipment, unless you are a full time storm chaser you are not going to get a shot that will sell - then again there is always luck...

    It is best to set up the camera in a dry place with some form of lightning rods.  I like to set the rig up in the garage (with the door open).  Many times I will turn on the rig in the middle of the night and go back to sleep.  I must stress the importance of using some form of lightning protection in a sever lightning storm.  When I was taking still photos of lightning and testing homemade camera designs I lived in Washington D.C. I used to walk to the George Washington Masonic Temple in Alexandra V.A. and film lightning strikes every night in the summer as the lightning storm rolled in.  Once when filming from the alcove at the front door lightning struck the building and rain down the lightning cable a few feet away.

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