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Covington Innovations Home > Astronomy and Astrophotography > Links > Digital SLR Notes > Non-Dedicated Flash with Digital Rebel
Using Non-Dedicated Flash with the Canon EOS 300D Digital Rebel
Here are some quick notes on how to use a non-Canon-dedicated flash with an EOS Digital Rebel. The same principles will apply to numerous other digital SLRs and electronically controlled film SLRs.
What is a non-dedicated flash?
I'm talking about 3 kinds of electronic flash units:
- Manual flash. This kind uses only two connectors (the central pin and the edge of the hot shoe) and does not regulate its light output. You have to calculate the aperture for your camera based on the film speed and the distance to the subject. The back of the flash usually shows a chart or scale to help you with this.
Hint: On a digital camera, exposing by trial and error is easy. (At last we are spared the long suspense that used to accompany flash photography!) Look at the histogram (press INFO in playback mode) to make sure an exposure is correct.
- Autoflash. This kind likewise uses only 2 connectors, but it regulates its light output using its own photocell, so that your camera can stay at the same aperture all the time. Most autoflashes also have a manual mode.
Hint: Use the manual mode when you want more power, e.g., to work at a small aperture for great depth of field.
- Flashes dedicated to non-Canon cameras. Caution! Such a flash will have extra pins on its foot, and you must make sure they don't contact anything on the Canon. With Olympus OM dedicated flashes, there's no problem because Olympus's extra pins don't touch any of Canon's extra connectors. Pentax flashes, I'm told, are the same way.
In this situation you must use the flash in manual or autoflash mode; obviously, the dedicated circuitry will not communicate with your Canon camera. The camera can only tell the flash when to fire, not how much light to emit.
Measuring the sync voltage
Do not skip this step! Before placing any non-Canon flash unit in the hot shoe of an EOS camera, you must measure the sync voltage with a voltmeter. Turn the flash on, not attached to a camera, and measure the DC voltage from the center pin to the edge of the hot shoe connector (hot foot?) when the flash is ready to fire.It must be 6 volts or less, with the center pin positive. Higher voltages will damage the camera. Reversed polarity will cause ERR 99, which you can clear by turning the camera off. Do not make any assumptions about the voltage; measure it! Some flashes put out as much as 700 volts and will fry your EOS.
If you are not familiar with how to use a voltmeter, it should be easy to find someone who is. People who repair TVs, radios, electrical equipment, or automobiles generally know how to make the measurement I've just described.
If you have a higher-voltage flash, there's a gadget called a Wein SafeSync that will interface it properly to your EOS.
Controlling the exposure on the EOS
To use a non-Canon-dedicated flash, you must use the camera in M (manual) mode. Turn the dial to select a shutter speed of 1/200 second. Then hold down Av+/- and turn the dial again to select the aperture (f-stop) that is prescribed for your flash and your ISO speed. Or shift it a little if you get over- or underexposures.There is no point in trying to work in Av (aperture-priority) mode because the flash does not interface with the exposure sensors in the camera.
Examples
I have had good results using a Vivitar ring flash (a plain autoflash, not dedicated to any camera's internal electronics) and a Sunpak 344D which is dedicated to Olympus OM and whose extra Olympus contacts don't touch anything on the Canon's shoe. The Sunpak has two auto modes for different power levels (yellow and green) and a manual mode. The Olympus dedicated mode is of course not usable.
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