School of Digital Media Arts GM 300BB

Washtenaw Community College Don Werthmann School of Digital Media Arts GM 300BB 973.3586 http://courses.wccnet.edu/~donw donw@wccnet.edu Introduction to Profoto Acute 2 Strobe Lighting System The transition from tungsten to strobe lighting can present a disruption in your studio workflow because there is a sudden increase of new ideas to keep track of. Remaining constant however, are the physical characteristics and properties of light you ve become acquainted with while using tungsten lighting. 3 PRINCIPLES of Light 4 TYPES of Light 5 DIRECTIONS of Light Allow yourself plenty of time to become acquainted with the equipment so that you do not damage it, your camera, or yourself. Strobe power generators draw a large amount of electricity that is stored in capacitors, which is then discharged in a fraction-of-a-second as a flash or burst of light. Please don't hesitate to ask questions before acting. Key Ideas: Shoot in a DAYLIGHT White Balance Mode (or film) when working with strobe The color temperature of strobe is between 5000 to 6500 Kelvin DAYLIGHT The light heads don t plug into an AC outlet, but into a power supply instead Strobe exposures occur in bursts of light known as FLASH DURATION and this property of strobe light takes the place of the shutter speed variable at the camera Aperture controls strobe light, shutter speed controls ambient light Multiple bursts (pops) function arithmetically, similar to time exposures Watt-seconds (Ws) This is a measure of energy within the power supply prior to it being discharged to the light head. In Europe the term "joule" is used. This term refers to the ability of the capacitors inside a power supply to store electricity. Watt-seconds are not dependent on reflectors, diffusers, etc, nor does it address the efficiency of energy usage and light output of the light head itself. Watt-second values vary proportionately, like ISO numbers do with film, so there are other existing values besides those mentioned below. 150 225 300 450 600 900 1200 1800 2400 3600 4800 1-stop of light Each time a watt-second value is doubled, the amount of light is increased by 1-stop for instance, a meter reading from f/16 to f/22. If a Ws value is cut-in-half, 1-stop of light is lost. Flash Duration s Relationship to Watt-Seconds & Shutter Speed 1200 Ws = 1/560 th sec. flash duration If a faster shutter speed is used with 1200 Ws (1/1000 th sec. or faster), then the image gets clipped, (underexposed) with a leaf-shutter camera such as a Hasselblad. The curtain shutter of an SLR camera synchronizes at speed determined by the manufacturer, and if the shutter speed is set faster than their given sync setting, then the curtain blocks an area of the frame gate producing a partial image. Sync speeds vary widely, so Read The Manual (RTFM). 600 Ws = 1/1000 th sec. flash duration Revealed in these figures is the idea that a decrease in watt-seconds value means there is also a decrease in flash duration, since it takes a smaller amount of energy less time to complete its on / off cycle. Therefore, a higher value in watt-seconds produces a longer flash duration. 300 Ws = 1/1800 th sec. flash duration 150 Ws = 1/3200 th sec. flash duration

Introduction to Profoto Strobe Lighting Systems pg. 2 of 8 Flash Duration A measure of time in regard to a burst of light. Generally speaking, a strobe light is on from the moment it reaches 50% of its peak value, until the moment it has diminished to the same value. The amount of watt-seconds (energy) that a strobe light receives determines its flash duration. More energy = longer time less energy = shorter time. Synchronization The camera's shutter is linked by means of a slave device to the synchronization terminal of the power supply, and when the shutter is released a circuit is completed, which triggers the strobes precisely during the full opening of the shutter. Sync Socket This single-prong (RCA) receptacle on the power supply is the location at which to link the camera by means of a synchronization device. Internal Slave Unit This device simultaneously triggers a power supply that is designated to be a secondary unit (or more) on the set, in response to the flash provided by the primary unit that is synchronized to camera. Since light travels at 186,000 miles per second, the distance of any primary light to the slave unit is instantaneous. All Profoto power generators have a built-in slave. External slave units vary in design, in that some are sensitive to a flash of light, some respond to pulses of infrared light, and some receive a signal from a radio transmitter. Synchronization Cords This hard-wire connection between camera and strobe power supply is not advisable for any digital camera system. Always use a radio-slave unit. Ready / Test Button The ready light illuminates when the power supply is at 100% recycle. Push the button if performing noncord metering, discharging power after reducing wattsecond distribution or the bracket dials, or to create a multiple-pop exposure, which is described later. Pocket Wizard Radio Transmitter & Receiver

Introduction to Profoto Strobe Lighting Systems pg. 3 of 8 Ratio Several lighting ratios can be created by means of close study of the chart on the right. Watt-seconds distribution refers ONLY to power output from the supply to the light heads. Meaning that the light falling on the subject will not be at the same ratio because of light to subject distance variations, or use of various lighting instruments like softboxes, honeycomb grids, gels, umbrellas, reflectors, etc. This chart appears on the side of each Acute 2, 1200 power supply Bracket Dial Simultaneously controls power distribution to both channels in the power supply, in ¼ stop increments, down to minus-2 stops. If power is decreased; power will not be reduced until the pack is discharged (dumped) once with the Test Button. Flash duration, recycle time and color temperature are all affected by using this dial. Its namesake means that it can also be used to create an exposure bracket, instead of using aperture or shutter speed controls at camera. Starting a bracket at the lowest desired minus setting, and then increasing power for each consecutive exposure is easier, since a power dump won t be required between each frame. Channel-A / Channel-B This 2-channel power generator enables the user to either combine or isolate the available energy so many different lighting situations can be created. There are 3-sockets for lights to be plugged-in to the pack: Channel-A has one socket, and Channel-B has two sockets. Note the chart s iconography that expresses ideas of Full, Half, and Quarter power. Energy distribution symmetrically or asymmetrically is possible. Combining channels is indicated on the chart as A+B, and isolating channels is indicated as A<>B. It s good practice to make sure that the ready light is illuminated before changing the A-switch and / or B-switch position.

Introduction to Profoto Strobe Systems pg. 4 of 8 Power Switch This on/off switch provides AC power to the internal capacitors, and the model lights. When switched off, any power accumulated in the capacitors is discharged automatically, allowing arcfree disconnection of lights. It is good practice to allow the capacitors to warm-up (form) a few minutes before starting your work session. Arc-over protection is built into the power supply. The safest method to change light head cables from one socket to another is to turn the supply OFF first. MOD.A / MOD.B Dials These adjust the intensity of the model lamps on the heads plugged into socketa or B, and can be matched to its respective light unit(s) so that lighting ratios can be pre-visualized. These dials do not change the energy output to the strobe lights. MOD.LIGHT Switch Combine / Isolate Switch (13) This switch determines how energy is being distributed between Channel-A and Channel-B. A+B is combines the two, A<>B isolates them. Examine the chart to determine the ratio being selected, based on the placement and number of heads used. It is good practice to place this switch at OFF when connecting heads to supply. MAX: model lights are always at full intensity. DIM: model lights intensity can be adjusted in with MOD.A / MOD.B dial to match ratio of strobe output on the set. This switch does not provide power for the strobe lights to operate. OFF: Model lights turned off do not compromise the exposure of strobe lights. You just won t be able to see what you are doing.

Introduction to Profoto Strobe Lighting Systems pg. 5 of 8 Fast/Slow Recycle Switch This allows you to adjust the amount of time it takes for power to draw out of the AC outlet into the pack. Slow draws 13 amps, Fast draws 20 amps, so make sure your AC outlet can provide sufficient amperage to support the draw of electricity to recharge the pack mostly a location issue, not so much a studio issue. Be sure the Ready light is illuminated before moving this switch. The power supply is plugged-in to a standard, grounded AC outlet that must provide a minimum of 13 amps. Any amperage lower than this cannot support the power requirements of the power supply during its recharge cycle and thus, a circuit breaker will be "thrown" in a power distribution panel. Model Lights These 250 watt, 3200 Kelvin, tungsten bulbs provide illumination to preview the direction and type of light on the set. They are designed to perform only as a simulated light source, not as a primary source for exposing. Model lights do not play an active role during an exposure unless the shutter speed is long enough to capture it. Model lights produce heat like any other tungsten lamp, yet they are fan-cooled when in a strobe head, for easier handling. As with any tungsten bulb, never touch the glass surface. Skin oils make an uneven distribution of heat occur which creates a bubble, making it burst prematurely. If you touch one by accident, it can be easily be cleaned with alcohol, when the light is disconnected. Strobe Tubes The design of these lights are that of a tubular glass coil which is mounted inside a (UV coated) glass housing. These tubes do not have a fixed wattage rating, like a tungsten bulb. Instead they are capable of transmitting a wide range of Watt-seconds from as little as 18 Ws, up to 2400 Ws. This is the light that illuminates the subject when an exposure occurs. Xenon-filled strobe tubes provide a daylight color balance, like mid-day sun ranging from 5000 to 6500 Kelvin, depending on the age (used hours) of the tube. Frequent, consecutive exposures do create some heat, but the fan in each head pushes air across the glass, keeping it cool. It is safe to touch the frosted glass housing with bare hands, but never touch the tubular coil inside for the same reasons stated for tungsten lights above. The model lamp is mounted in the light head in such a way that the strobe tube surrounds it.

Introduction to Profoto Strobe Lighting Systems pg. 6 of 8 Profoto Acute 2 Head A general purpose, heavyduty light that includes a quiet, high-efficiency cooling fan. All heads have a model light switch (9) that can be turned on / off, in addition to MOD.LIGHT switch on the power supply. Several light shaping tools can be attached to the head, like reflector dishes, honeycomb grids, snoots, softboxes, umbrellas, etc. Speedrings These devices are required to enable any softbox to be mounted to a light head. Parabolic Dish Reflectors of various sizes; 7", 9", 11.5", etc, attach to heads. Honeycomb Grids mount in reflector dishes; 10, 20, 30, 40 Profoto speedrings do not work with any other strobe manufacturer s light heads, and vice-versa. Umbrellas These are easily attached by means of inserting its stem into a receptacle located at the base of the head (2). Umbrellas are designed to work as either diffused light or reflected light sources.

Introduction to Profoto Strobe Lighting Systems pg. 7 of 8 Snoots attach to a reflector dish to shape light similar to tungsten lighting systems. Softboxes are manufactured in various shapes and sizes. The correct choice of softbox is based on the size of the subject matter. The optimum light-to-subject distance is its shortest edge dimension. Sync Terminal Measure the intensity of strobe light by placing the meter in CORD Mode; then connect the Pocket Wizard Transmitter to the sync terminal of the meter with the ¼ phoneto-pc sync cord. Connect the Pocket Wizard Minolta Auto-Meter IV F In the CORD or NON.C Mode, the Receiver to the sync socket on the power supply meter cannot toggle to equivalent with the ¼ phone-to-rca sync cord. exposure values, as it does in the AMBI Pushing the measure button triggers the strobes, Mode. The meter is behaving like this and produces an f/number reading. because it is measuring the intensity of a flash of light, which occurs in a fraction The NON.C Mode measures strobe without a of a second. The variable of time (shutter sync cord attached to the meter. Push the measure speed) cannot be measured (and then button once to reset it; have an assistant push the reinterpreted with another f/number) Ready button on a power supply; the reading will because the idea of time is built-into be displayed. the flash of light itself flash duration. Therefore, be mindful that aperture controls strobe light, shutter speed controls ambient light. Think about what you already know Then take it a step further With ambient light sources, there are three variables that make an exposure. The variable of sensitivity film or digital camera ISO number The variable of time controlled by shutter speed The variable of intensity controlled by aperture With strobe light, there are also these three variables, but they function different. The variable of sensitivity film or digital camera ISO number The variable of time controlled by flash duration (which is dictated by watt-seconds) The variable of intensity controlled by aperture

Introduction to Profoto Strobe Lighting Systems pg. 8 of 8 For non-believers, try this If you are still confused, and having a hard time believing that shutter speed doesn t control strobe light, do this quick test on your set, with a light meter. In CORD Mode, toggle the shutter speed to 125 th sec., then take an exposure reading of one of the strobe lights on your set. Record or memorize this f/number. Stay in CORD Mode, and now toggle the shutter speed to 1/8 th sec., then take another exposure reading, positioning it exactly like in the first step. The f/number is most likely identical, or just a few 10 ths of a stop off. With ambient light, it makes perfect sense to think, and fully expect, that a drastic change in shutter speed like this would change the aperture also. Strobe isn t ambient light, it is a FLASH. It does its business in a fraction of a second. Therefore, the identical f/number measurements between the two readings are telling you that the aperture must be set there because of the intensity of the flash of light at that specific subject to light distance. Generally speaking You might notice that if the meter s shutter speed is set at a relatively slow time, the measurement will take into account the ambient light on the set (from the model lights) in addition to the strobe light. So as a rule of thumb, always make strobe measurements with the shutter speed set around 1/125 th sec; and that holds true for the shutter speed ring at the camera, too. Bracketing with Multiple Pops With ambient light, we can maintain depth-of-field by staying at one f/number throughout a five-way exposure bracket, and then using time to make half-stop increments. The same arithmetic works with strobe; the major change is inherent in the behavior of the light from that of a continuously burning nature, to that of a burst of light. Compare these brackets: Ambient Light Strobe Light +1 f/32 @ 8 sec. +1 f/32 @ 8 pops +1/2 f/32 @ 6 sec. +1/2 f/32 @ 6 pops N f/32 @ 4 sec. N f/32 @ 4 pops -1/2 f/32 @ 3 sec. -1/2 f/32 @ 3 pops -1 f/32 @ 2 sec. -1 f/32 @ 2 pops Each time a value is doubled, one-stop of light is gained. Each time a value is cut in half, one-stop of light is lost. Procedures for Multiple Pop Exposures Disconnect the Pocket Wizard Radio Transmitter from the camera. Set the camera shutter speed to B (bulb), then set the aperture to desired f/number Turn-off the modeling lights at the power supply turn-off all house lights too With cable release; open the shutter and hold open until last pop is complete Allow the power supply to fully recycle between each consecutive pop!!! Sources: Profoto Acute 2 User Manual http://www.speedotron.com http://www.calumetphoto.com Photographing in the Studio, Gary Kolb, Chapter 6, pg. 80 84 Instruction Manual for Speedotron Black Line Equipment, pg. 9 12 & 31 rev. 08/2010