The picture below shows the interior of a ”stock” Vivitar 283 module. You can see
the two contacts that are “shorted” (soldered together). You can also see the two
contacts that will be connected to the resistors, the ones with the red and black
wires attached. (This picture is from the standard 283 sensor that included a photocell
for “automatic exposure”. When used solely with resistors, there are no “polarity
Note that there is a 200pF capacitor across the leads to the variable resistance.
Prior to using 283’s for microscope illumination I had used them for many years for
other “high speed” photography projects. The controls I used for those projects did
not have this small capacitor, and they worked fine. Since Vivitar made their modules
with this component in place I assume there was a reason... so I incorporate it in
Note: As mentioned above this flash model was made for many years. The earlier models
had a high voltage across the sync terminals. The voltage levels are too high for
some of the newer electronic cameras, and could seriously damage these cameras. Units
that were made later in the products life span had a much lower, safe, sync voltage
level. While units manufactured in Korea or China are often said to be safe for all
cameras, I would err on the cautious side. If you have the proper meter and knowledge
to check the unit you will be using, you can measure it and compare the results to
your camera specs (if you can find them!).
A worry-free way to incorporate older electronic flash units with modern digital
cameras is to use a device such as a Wein "safe-sync" (or a Paramount Vivitar sync
cord with “voltage protection”) that insures the sync voltage is sufficiently low
so as not to damage the camera electronics. Of course, a flash can always be safely
"fired" using a flash slave unit, with a camera manufacturers flash on the camera
(or built-in camera flash if present) set to a very low setting.
The picture below shows a finished “control box” and a flash unit.
I have used two 12-position switches. The upper switch provides setting from “FULL“
to “-5.5 stops”. When toggled to the lower switch, the power settings go from “-2.5
stops” to “-8” stops”. Having exact, discrete positions for ½ stop increments has
The center contact is not used.
The two contacts on the left side of the picture above, one at "10 o'clock" the
other at "8 o'clock" must be connected ("dead short") to each other.
Using the Vivitar 283 for Photomicrography
A versatile manual power control for the Vivitar 283
My desire to photograph active, live subjects through the microscope necessitated
the use of electronic flash. This page does not cover the method used to implement
the flash illumination on the microscope, but provides information about controlling
the light output (and as a result the flash duration) with the Vivitar 283 flash
unit. If you wish to see how the flash unit was incorporated into the microscope
illumination see the page on my current setup, as well as an earlier implementation.
I settled on using the venerable Vivitar283 primarily because it allows easy and
remote (via wire) setting of power levels. The lower power levels give very short
flash durations that have great motion stopping ability. I had tried using a TTL
flash unit, but found I wanted to make + or - adjustments fairly often, and the location
of the flash and camera made this cumbersome. With the feedback provided by digital
cameras (histograms, image review) manual flash is not a problem, in fact it has
become my preferred method. The Vivitar is now a “discontinued” model, but it had
been made for a very long time, were (are!) extremely popular, and there is an ample
supply on eBay and in the used equipment cases of many camera stores.
Vivitar made a “VariPower” module for this flash, and they also made a remote cord
so that this module could be used some distance from the flash. The VariPower is
nothing more than a simple (but custom) variable resistor. I have always found the
VariPower hard to reset to exact values, or in small increments. It was intended
to plug into front of the flash, so it is necessarily small. The adjustment is non-linear
and at reduced settings a small movement of the dial makes a large difference in
the resistor value. When incorporated into a microscope setup, it is highly advantageous
to have a larger control control “box” with exact, repeatable positions. The tabletop
control shown below has discrete, ½ stop increments and has worked superbly.
The picture below shows the two contacts on the front of the unit that are used to
change power levels. You only need to vary the resistance between these contacts.
The control box I now use is set up using multi-pole switches with discrete resistor
values at each switch position.
* all units went down to at least -7.5 stops. One went to -8 and two others were
250K ohm or greater
To determine the values for the resistors, four Vivitar283's (all were "used" units)
were carefully tested. Using a Sekonic flash meter, the resistance values required
to decrease the power in "stops" were determined. There was a small difference from
unit to unit. The values listed here are the average, and they have proven to work