Using the Vivitar 283's light sensor socket
When the light sensor module on a Vivitar 283 is removed, a 5-hole socket is revealed as shown in Figure 1. Connections can be made directly to this socket to a) discharge the flash unit and b) control the flash duration. These connections will be described below. In order to simplify the discussion, the 5 holes will be referred to by number as shown in the diagram below.
a) Discharging the flash unit Holes 1 and 3 of the socket are the positive and negative terminals respectively of the flash unit's trigger circuit. Shorting from one hole to the other with a wire will discharge the flash unit. The output of a sound trigger or photogate could be connected to the flash unit this way as an alternative to using a PC cord. b) Controlling the flash duration Holes 2 and 5 are the connections to the auto-exposure circuit. Normally, the photocell of the sensor module would bridge these holes. The photocell provides the equivalent of a variable resistor whose resistance decreases as the light intensity on the cell increases. The lower the resistance, the shorter the flash duration will be. Thus, if the photocell is replaced with a wirewound variable resistor, the same function can be obtained with the turn of the resistor dial. By turning down the resistance, the flash duration will be shorter. In many cases for high-speed photography, the minimum possible duration is desired. This is achieved simply by shorting across holes 2 and 5. In cases where the motion to be photographed is not particularly fast and greater light intensity is desired, the resistance can be increased in order to achieve that intensity. One example is in photographing splashes of liquid drops, a relatively low-speed phenomenon compared to, say, bullets and balloon bursts. Since the subject is quite small, one has to work at close range with a macro lens in order to achieve good photographic results. Depth-of-field is problematic at these close distances, and small lens apertures are needed. This requires more sensitive film and/or more light on the subject. If one wants to work with a fine-grain low-speed film, then boosting the light output of the flash unit makes sense. If one does adjust flash duration/intensity using a variable resistor, determining the lens aperture for correct exposure of the film is not as simple as when the Vivitar's sensor is used. (The

1999 Loren M. Winters

automatic-exposure circuit is calibrated to provide correct exposure when the flash unit is used according to manufacturer's instructions.) Here are some ways to select the lens aperture when a variable resistor is used in place of the sensor. i. exposure testing: Take a series of photographs of the same subject under the same conditions using a series of aperture settings. Develop the film and select the aperture that gives the best exposure. This can then be used as a starting point for photographs taken under different conditions. ii. metering: If a flash meter is available, this is the easiest way to determine the correct aperture. It's a good idea to use an aperture one stop larger (smaller f-number) than the flash meter indicates. Flash meters are calibrated for situations where the background and surroundings have high reflectivity. This is just the opposite of the conditions under which high-speed photographs are usually taken. iii. rule of thumb: The rule given below is based on some measurements taken with a flash meter.
With ISO 100 film and a flash-to-subject distance of 1 meter, the lens f-stop is found simply by adding 2 to the value of the resistance (in units of kilohms). This empirical relationship holds well up to 6 k. Having adjusted the intensity with the variable resistor, one also wants to know that the flash duration is not too long for the subject being photographed. Here's a rule of thumb for estimating the flash duration, given the resistance, R. (See the article given in the footnotes1 for a description of how this rule was determined.) For R = 2 to 100 k, the flash duration is given simply by t = 17R, where R is given in kilohm and the flash duration, t, is given in microseconds. Below 2 k, the duration falls less rapidly, reaching a minimum value of about 20 s. 2 Example: If R = 6 k, then an aperture of f/8 could be used with ISO 100 film at 1 meter from the subject. For this resistance, the flash duration would be about 100 microseconds.

See the Appendix of this article: "High-Speed Photography with Sound Triggers," L.M. Winters, The Physics Teacher 28, 12 (1990). 2 These measurements were taken with the flash head in the horizontal position. If the head were in a bounce position, C would be about a third greater. This is due to the fact that in any of the bounce positions, the capacitance of the exposure control circuit is increased by about 30% to provide the extra light output needed for bounce illumination. Reference: Vivitar Service Manual, Automatic Electronic Flash Model 283, pub. no. 3746059, revision C (1984), p. 5.

Operating Guide for

Vivitar 283 & 285 flashes

MODES OF OPERATION

There are multiple methods for taking pictures with these flashes: Using the automatic exposure control, using partial power or determining the flash manually.
Media Loan Operating Guides are also available online at www.evergreen.edu/media/ml/
N Care must be taken as burns can occur from touching hot parts. N Do not operate flash if it has been dropped or damaged until it has been examined by a Media Loan assistant. N Let flash cool before storing. N Do not get the flash wet. N Do not use with digital cameras. Powering on
The power switch on the back of the flash should show red for the power to be ON. The flash will emit a high pitch as it is charging, and when it is ready, the Open Flash control lights. If the Open Flash push-button blinks, this is indicating a battery-saving circuit is in operation. If the button does not light within 30 seconds, your batteries should be replaced.

General Precautions

Setting focal length on the 285
When using different focal lengths with the 285 you can adjust between wide (35), norm (50/55) and tele (105). 28mm wide inserts and diffusers are also available.

Calculator Dial

On the end of the flash hinge is the calculator (calc.) dial with three concentric inner rings, and one outside. The calculator dial is not connected to the flash and does not control functions. It is a tool to help you find the correct aperture setting for your camera based on distance from your subject, ASA of your film, or flash power setting (285 only). You will want the camera's shutter speed set to recommended settings. Media Loan's cameras should be set to 1/60 of a second, or "x".
Using the Dial on the 283
Select your film speed (ASA) by turning the dial until the black arrow lines up with your desired setting. Either estimate or measure the distance from the flash to the subject being illuminated. In the colored section go to the distance in either feet (ft) or meters (m). Set the thyristor (sensor unit on the front of the flash) to the color shown and your camera to the number given in f-stops above that color.
The flash uses four (4) AA batteries which fit into a holder in the battery compartment, next to the swivel head hinge, or with an optional AC power adapter the flash can be plugged into a standard wall outlet for power (this adapter is available through Media Loan). To insert the batteries, rotate the head to the 0 degree position, and slide the battery compartment door toward the rear of the body. Do not try to completely remove the compartment door. It stays attached to the flash unit. The holder may now be removed. Align the +/- ends as indicated on the holder body. 1. Open Flash Button Use alkaline batteries, others may 2. Thyristor (Sensor Socket) be cheaper, but they will not last 3. Battery Compartment Cover as long and may not function 4. Illuminated Calculator Dial properly. Insert so the bare ends 5. ASA/DIN Indicator Arrow of the cells enter first. Press the 6. Lens/Filter Slot holder into the cavity, and hold it 7. Zoom/Bounce Flash Head down against the spring pressure 8. Zoom Setting Indicator as shut the cover. 9. Bounce Angle Scale
10. Sufficient Light Indicator 11. Calculator Dial Light Button 12. On-Off Switch 13. Ready Light 14. Mounting Foot Lock Lever 15. Mounting Foot 16. Shutter Cord Socket 17. AC Adapter Receptacle
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Vivitar 283 & 285 Flashes
Using the dial on the 285
If using an automatic mode: Select your film speed (ASA) by rotating the outside ring. Make sure the next ring has the black arrow pointing at FULL. Now using the distance from flash to subject find the distance on the inner most ring, again in either feet (ft) or meters (m). Using the color that covers your distance range, set the thyristor, and your camera using the f-stops given just above the distance and color indicators.

Thyristor (Sensor socket) Settings
M - Manual, the maximum amount of light will be output in this setting at all times. When in manual mode you can determine F-stop using the calculator dial, but disregard the color bands. Yellow - The widest lens opening for shallowest depth of field. This will allow the greatest depth of flash illumination while in an automatic mode, from 5 to 43 feet. Red - A medium lens opening for greater depth of field, but shorter operating distance, from 4 to 30 feet. Blue - Greater still depth of field, shorter depth of illumination, 2 to 15 feet. Purple - Maximum depth of field, smallest aperture and minimum range of illumination, 2 to 11 feet.
i If using partial power settings: Select how much power you wish to use by adjusting the dial on the thyristor (1/16, 1/4, or 1/2). Select your film speed (ASA) with the outermost ring, and what power you wish to use with the next ring in. As with the auto modes, find your distance and set your f-stops accordingly. Auto Exposure Control
On the front of the flash is the Auto Thyristor Sensor. This small device detects the amount of light present when the flash is triggered, metering the level of illumination on the subject. The outer collar of the sensor is the mode selector. This rotates to set for different aperture ranges while in the automatic mode, or to set for manual operation. Holding the unit upright and pointed to the right, the small window on the side of the sensor shows the ranges in different colors, flash power or M for manual.
Sufficient Light Indicator
The SLI will slow for 2-3 seconds after a flash if the sensor reads the correct light level during the illumination. You can check your exposure before taking a shot by manually triggering the flash unit and watching the SLI. If it doesn't light, you can do a number of things to correct the illumination. Set the Mode Selector to a value which will allow a wider f-stop and reduce the subject and flash distance; bounce the light from a more reflective surface.
i The SLI will not work in manual mode. Flash Guide Numbers
Flash guide numbers will help you calculate f-stops for exposures using the manual position or when you bounce your illumination. Measure the flash-reflector-subject distance, and divide the total into the Flash Guide number listed for the ASA film you are using. Round off the result to the nearest f-stop and open one stop wider. Example: using ASA 25 film with a camera-reflector subject-distance of 20 feet -- Guide #20 divided by 20 equals 3 (f2.8 approximate) open an additional stop to f2. You can estimate flash bounce settings in other ways. In average rooms, a general rule is to open two stops from where you would set a direct shot. OR, using the Calculator Dial, estimate the camerareflector-subject distance and open one more stop from what is indicated on the dial.

Bounce Lighting

In situations where reflective surfaces are above your subject, you can "bounce" the light from the flash unit off the ceiling to diffuse the illumination. This will reduce shadows and soften the glare normally associated with flash photos. When using bounce techniques, be sure to calculate the flash to reflective surface to subject distance when setting the f-stop. The reflective surface's light absorption characteristics will affect the amount of illumination that gets to the subject. The color will also be transmitted to the subject, so choose neutral colored surfaces. When bouncing off absorbent surfaces, open the calculated f-stop one additional stop. GUIDE NUMBERS:

ASA Guide # 120

100 135

125 150

160 170

200 240

400 340