For a low budget short I will have many day exterior scenes (in moving and parked car and on the street)
where I initially thought using only scrims, reflectors and negative fill, because I was afraid adding light
would slow us down too much.
But we are in winter and being in the mountains the weather (and light) can change very dramaticaly in
very little time so I thought that if I took only one single but very powerful artificial source it could not slow
us down so much and would up the results noteably.
I have always found reflector boards and overheads to be useless under rapidly changing conditions. They work great in modeling your talent when the sun is out, but as soon as the sun goes behind a cloud they are useless, resulting in the shots of even a short scene not matching when you get into the editing room. I agree with Jacques that you definitely need a large HMI source. A 6k will work, but as Albion points out it will require a large generator and all the baggage that comes with it. A better choice would be the Arri M40. It has the output of a 6k Par but you can run it, along with other lights, on a 7500W modified Honda EU6500is/Transformer gen-set that provides a single 60Amps/120V circuit.
Like all M-Series lamp heads, the M40 is equipped with MAX Reflector Technology, a unique and very bright open face reflector design that combines the advantages of a Fresnel and the output of a PAR in one fixture. Focusable by the turn of a knob (from 17-55 degrees), the MAX reflector produces a remarkably even light field and a crisp, clear shadow. The elimination of spread lenses, makes MAX reflector lamp heads comparable to par configurations of even a higher wattage. In fact, the M40 is brighter than some 6K PARs on the market.
To power the M40, ARRI has engineered a dual wattage ballast that will operate on supply voltages ranging from 100-250V. With Active Line Filtration (ARRI's system of Power Factor Correction) built in, the M40 ballast is incredibly efficient and generates virtually no harmonic noise - enabling it to reliably operate on portable gas generators like our 7500W modified Honda EU6500. And drawing only 36A at 120V, the M40 leaves room (24A) on the 60A circuit of a 7500W modified Honda EU6500is/Transformer gen-set for other lights, even their M18.
The approach that I find works best to maintain continuity in rapidly changing light is to shoot the establishing master shot when the sun is in a backlight position. Shooting into the downside of your talent, a M40 is large enough to create a sunny feel in a fairly large frame. Up to that point I shoot the close coverage under a full silk. Shooting the coverage under a silk offers a number of advantages. If the sun is coming in and out of clouds, the silk takes the directionality out of the sun and knocks down its’ level by two and half stops so that again a M40 is large enough to create a sunny feel in your close ups.
A good example of this approach is a scene I lit for a low budget feature that took place around a campfire in a small clearing surrounded by woods. Surrounded on all sides by woods, we knew that we would lose direct sunlight in the clearing early in the day and would need lights. We also knew that the scene was going to take all day to shoot because of its’ extensive dialogue, so we figured out where the sun was going to be throughout the day and where it would look best for our establishing wide shot. Where it was a two shot, mostly over the shoulder of one character talking to the second character who was standing with his back to the campfire with the woods behind him, we decided to wait until the sun had moved into a near back light position to shoot the establishing shot. So we shot our close coverage first with nothing more than a 4k Par and 1.2k Par under a 20x light soft frost on top of which we threw leaves. The 4k was heavily diffused and positioned so that it gave the talent the most attractive modeling. The 1.2kw was positioned as a backlight where the sun would be when we would eventually shoot the wide - this way there was always an edge in every shot for continuity.
When the time came to shoot the establishing shot, the shadow of the overhead frame and stands were thrown forward and did not interfere with the wider framing. Since we were still shooting under the Frost, we were wider open on the iris and so our exposure dug into the dark woods and brought out more detail. As an unexpected added bonus, the smoke from the campfire drifted into the woods, creating shafts of light where the sun broke through the tree canopy. What would have impossible to cut together without lights, turned into a beautifully lit scene, and was accomplished with nothing more than what could be powered on a modified Honda EU6500is generator.
Guy Holt, Gaffer, Screenlight and Grip, Lighting Rental and Sales in Boston.