Visual Effects Lighting With Kino Flo

Transcription

1 Visual Effects Lighting With Kino Flo Bluescreen and greenscreen lighting for computer generated imaging has evolved along with the advancements in digital extraction and compositing technology. As the leader in visual effects lighting, Kino Flo has compiled some tips and techniques to help demystify this specialized field.* *Adapted from information published in Flo Works Issues II and III, Vol. Three, Click on a link, or simply scroll down: The Kino Flo Advantage Kino Flo vs Quartz with Blue Gel Kino Flo vs Quartz with Green Gel Tips On Visual Effects Lighting For Film Techniques for Fixture Placement EV-to-Fixture Conversion Tables Densitometer Readings: Kino Flo Lit Bluescreen Tungsten Lit Bluescreen Kino Flo Lit Greenscreen Tungsten Lit Greenscreen Reverse Redscreen Lighting with Kinos Redscreen Lighting Suggestions Redscreen Graph Have questions or comments? Click here. The Kino Flo Advantage Kino Flos operating Super Blue lamps or Super Green lamps are inherently superior in lighting quality to any source when lighting painted cycs, bluescreens or greenscreens (see spectral graphs) because: Super Blue lamps emit pure blue light (420 nanometer spike); Super Green lamps emit a pure green light (560 nanometer spike). There is almost no contamination of the adjacent colors.

2 Kino Flos put out 10 times as much light per watt as tungsten sources. Kino Flos are a lot cooler and have a softer, more even beam spread. Kino Flos can control light levels without a change in color temperature. The three most commonly used colored backgrounds are "Tempo" and "Ultimatte," (both have a matte finish) and "Super" (a shiny finish). The backgrounds are either fabric or painted cycs. The fabrics reflect light more evenly than the paint, and are easier to set up; Super colors are brighter than the Tempo or Ultimatte colors, by about two thirds to a full F-stop. However, Tempo and Ultimatte materials can absorb contaminating colors better than Super paints and fabrics. KINO FLO VS QUARTZ with BLUE GEL: KINO FLO VS QUARTZ with BLUE GEL: At left, 420NM Super Blue Kino Flo light (line k) thoroughly saturates the blue area of the spectrum, while the 3200Kelvin quartz light (line q) barely registers a blip in same region. Kino Flo EV: 10.6 Quartz EV: 12 Kino 211FC 1000 FC Screen: Tempo Blue Gel: Rosco Calcolor 4290 KINO FLO VS QUARTZ with GREEN GEL: KINO FLO VS QUARTZ with GREEN GEL: At left, 560NM Super Green Kino Flo light (line k) thoroughly saturates the green area of the spectrum, while the 3200Kelvin quartz light (line q) is flat by comparison. Kino Flo EV: 9 Quartz EV: 9.6 Kino 222FC 155 FC Screen: Tempo Green Gel: Rosco Calcolor 4490 Tips On Visual Effects Lighting for Film Always shoot a film test to determine the true ASA of the film stock, the Exposure Value (EV) and color density. Spot meters vary widely when measuring blue light; some brands are as much as three F-stops from other brands. Always use the same meter for testing as for principle photography. Kino Flo lit bluescreens are typically best illuminated at ½ an F-stop to 1½ F-stops EV below nominal key, depending on the meter. Kino Flo lit greenscreens are usually best illuminated at key to a full F-stop below key, depending on the meter. Film stocks react differently to reflected green light than to blue light. The green layer of Kodak 5248, 5279, 5293, and 5298, for example, creates an ersatz matte line photochemically on highlight edges that must be fixed in post production. However, with pure blue light, the

3 anomaly barely shows up. Note: Kodak has developed a "hybrid" color negative film stock specifically for visual effects lighting called SFX 200T. The new stock does not register the type of edging seen in film types mentioned above. Illumination contrast the difference between foreground lighting and background lighting can assist in the matte extraction process. However, too much contrast can devalue the matte. Many DPs prefer a blue background when foreground plates include warm colors, such as lighter skin tones. When the foreground subject is biased in the cooler range, a DP may prefer a green background. Techniques for Fixture Placement To estimate the number of Fixtures for a job, see the sample conversion table. Rule of thumb on Fixture placement: divide the cyc height by two, rig the row(s) of Fixtures on five or six foot centers at that distance (i.e., on a 20ft high cyc the Kinos would be 10ft from screen.) A row of Fixtures at the top and bottom of the cyc will light the surface evenly. Extend a row of lights at least one Fixture beyond each end of the cyc to reduce drop off. Or, run some lights vertically along the ends of the cyc. Some cycs can only be lit from above. On cycs that are 30 feet or higher, the crew often will hang two rows of Image 80 Fixtures from the grid for better brightness and evenness. 20x20 4 Bank Front View 20x20 4 Bank Side View 20x20 Image 80 Front View 20x20 Image 80 Side View EV-to-Fixture Table: The following EV-to-Fixture tables were created within these parameters: A Pentax Digital spot meter was used for calculations. Other meters may vary. The tables measure Kino Flo Super Blue light reflected off a Tempo bluescreen.* The Fixtures were mounted on five-foot centers. (Beyond five Fixtures in a row the EVs level off.)

4 Kino Flo Image 80s (5ft Centers) 1 unit ft ft Distance From Bluescreen 8ft ft ft ft ft ft ft * EV readings for a Tempo greenscreen lit with Super Green lamps were the same as the above values or about 1/3 an F-stop lower. Kino Flo 4ft 4Banks (5ft Centers) 1 unit ft ft Distance From Bluescreen 8ft ft ft ft ft ft ft * EV readings for a Tempo greenscreen lit with Super Green lamps were the same as the above values or about 1/3 an F-stop lower.

5 Densitometer Readings The densitometer readings for the four tables below were taken on Kodak , ASA /50 Sec. The spot meter was a Pentax Model V. Tests were conducted by cinematographer Chuck Schuman for the movie The Ghost and the Darkness (1996). Table #1 +/- N RED GREEN BLUE N / Table #1 Kino Flo Lit Bluescreen: The densitometer table at left indicates the amount of color saturation in each layer of the film exposed under a narrow-band Blue fluorescent lamp running on a Kino Flo highoutput ballast. The "N" column records the F-stops above and below the nominal key of f/4.0. The Laboratory Aim Density (LAD), a measurement of the optimum color saturation in the Red, Green and Blue film layers, was recommended by a post production facility. A film test was then shot to find the proper Exposure Value (EV) to achieve the "correct" LAD. Here, the LADs were: Red,.20; Green,.90; Blue, Values above.20 for Red and.90 for Green degrade the matte. Values below.20 and.90 respectively improve the matte. The high ratio of Red/Green densities to Blue indicates the relative purity of the fluorescent light. Table #2 +/- N RED GREEN BLUE N / Table #2 Tungsten Lit Bluescreen: The table at left records the densities of 3250Kelvin tungsten light reflected off a bluescreen. Note the Blue densities at each F-stop are much lower than on the fluorescent lit screen. Conversely, the Red/Green values are higher than optimum LAD densities and will significantly pollute the Blue matte. Even if double CTB gel is added to the tungsten lamp, the Blue values do not improve and light output is reduced by more than 80 percent! In addition, double CTB cuts the Red/Green transparency only by half, and yet the Red/Green to Blue ratios remain significantly lower than the fluorescent lit

6 bluescreen. Table #3 +/- N RED GREEN BLUE N / Table #3 Kino Flo Lit Greenscreen: The densitometer table at left indicates the amount of color saturation in each layer of the film exposed under a narrow-band Green fluorescent lamp running on a Kino Flo highoutput ballast. The LAD values for the greenscreen were set at: Red,.22; Green, 1.60; and Blue, For the reasons listed in the bluescreen tests above, the fluorescent lit greenscreen is far superior to the tungsten lit screen. However, it is interesting to note that the EV for this test was at 8.6, a full stop brighter than the EV on the bluescreen, yet the ratios here are not as good as the bluescreen. So, while this greenscreen appears brighter than bluescreen, narrowband Blue light saturates the Blue layer of film more efficiently than narrow-band Green light saturates the Green layer. Table #4 +/- N RED GREEN BLUE N / Table #4 Tungsten Lit Greenscreen: The table at left records the densities of 3250Kelvin tungsten light reflected off a greenscreen. The same problems seen in the tungsten lit bluescreen test are evident here in the Green layer as well. Ratios remain very low even when Green gel is added to the tungsten lamp. Reverse Redscreen Lighting with Kinos

7 The reverse redscreen process is used when light from a color difference "bluescreen" system would reflect off the subject and corrupt matte extractions for compositing. The technique uses a long-wave ultraviolet fluorescent source (black light) to excite the rare earth phosphor in the red coating. Ultraviolet light used for the reverse process is made invisible to the film by using a high-pass filter on the camera lens, such as a Wratten 23A or 25. The Wratten filter cuts out all light in the energy spectrum below 600nm, including the 360nm ultraviolet light and mercury spikes in the blue and green light bands. However, the ultraviolet light energy stimulates the rare earth element to fluoresce at 620nm (see graph). The optimum peak saturation for the red layer of Kodak film stocks is close to 650nm. Basically, the redscreen under ultraviolet light becomes the illuminating source. Anything in the foreground ultraviolet light not coated with the red phosphor will create an unexposed silhouette on the film. Note: It is possible to black light a green or bluescreen for a reverse matte process using other filters, however, the reflected colors are not nearly as bright and there is significant pollution from adjacent color layers, according to an Eastman Kodak spokesman. Redscreen Lighting Suggestions Shoot a film test to determine color saturation densities and exposure values. Use a Wratten 2A or 2B filter over your spot meter cell to improve sensitivity to colors that fluoresce under ultraviolet light. Do not use any gel based diffusion on fluorescent blacklights. It will diminish the ultraviolet light output. Keep a reference plate of the red screen for later use. Output is optimal when lamps are well ventilated. Ultraviolet-blocking eyewear should be worn when operating lamps. Skin should be free of cosmetics. People who are on medication should not work under ultraviolet light. Red Screen Graph The spectrometer reading to the left records an illuminating redscreen under 360nm ultraviolet light. The wavelength in the red band on the right side

8 peaks around 620nm. Kino Flo Sales - Tel: (818) Fax: (818)