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D-SLR Flash Voltage Introduction
With the advent of sensitive digital cameras, there has been much discussion on the web about the danger of using older photo flash strobes on the hotshoe connector. The primary concern comes from the two major SLR manufacturers, Nikon and Canon, listing the maximum hotshoe X-sync voltage being no higher than 250V and 6V, respectively. Many older flashes had a trigger voltage of over 200V on the X-sync contact relative to the mechanical ground shoe connector. This high voltage has the potential to damage or destroy expensive modern digital cameras.

I took all of the flashes out of my arsenal of photographic equipment to measure to determine what the exact X-sync voltage is for each of them. Now that I shoot with Nikon digital, I only use Nikon SB-800 flashes so I never have to worry about any compatibility problems. I've never had a reason to use some of the older flashes and after measuring the voltage on each of them, I'm glad I haven't. Several of the flashes have X-sync voltages above 200V!

The reason older manual cameras did not suffer from damage from high voltages present on the X-sync contact is that mechanical metal contacts were used to fire off the attached flash. This means that there is no reasonable voltage that could damage the contacts. However, modern digital cameras use CMOS open-collector drive circuits which can only withstand so much voltage.

X-sync measurements
Each flash was measured with a Fluke 77 Multimeter, a high-quality professional tool. Each of the flashes was powered with 4 brand new alkaline batteries to insure the correct operating voltage was present in the flash.

Below are images of the flash unit under test, the test probes and the actual measurement of the X-sync voltage displayed on the Fluke 77 Multimeter.

 2006 Aaron Linsdau

Vivitar 2000 Electronic flash measures 220V on the X-sync contact

The X-sync voltage on the Vivitar 2000 far exceeds the maximum rating of 6V on Canon cameras and nearly exceeds the maximum 250V on Nikon cameras. Since it is likely that when firing the X-sync contact could experience a voltage spike in excess of 250V, this flash is not safe to use on any modern digital camera.

 2006 Aaron Linsdau

Vivitar 285HV Zoom Thyristor Vari-power flash measures 7.84V on the X-sync contact

The X-sync voltage on the Vivitar 285HV flash is low enough for Nikon cameras, based on the statement in their user manuals, but not for some Canon cameras which claim a maximum voltage of 6V on their hotshoe connectors. The Vivitar 285HV flash is one of the more popular non-digital dedicated flash gun units but does not provide modern digital TTL operation on Canon or Nikon cameras.

 2006 Aaron Linsdau

Tristar 320TZB flash measures 237V on the X-sync contact

Measuring the Tristar 320TZB flash unit was scary because there is no external connecting cable available so the meter probes had to be stuffed into the hotshoe mechanical assembly and held while the Kodak Easyshare CX7530 fired off the self-timer. This flash is definitely near the maximum rating of Nikon cameras and puts the camera in the danger zone of operation. See this article regarding the operation of this flash unit.

 2006 Aaron Linsdau

Nikon SB-30 flash unit measures 4.63V on the X-sync contact

The Nikon SB-30 flash unit is well within the safety margin for both Nikon and Canon digital cameras. However, this unit provides none of the modern capability of i-TTL and E-TTL operation, reducing this flash to a manual operation flash. It will work when no other equipment is available but it does not come close to the flexibility and power of the more modern flash guns.

 2006 Aaron Linsdau
The Metz 44 AF-4i N, the Metz Nikon TTL version flash gun measures 4.71V on the X-sync contact

The Metz 44 AF-4i N is within the safety margin for both Nikon and Canon Digital cameras. This particular model is programmed to work with Nikon TTL operation. If you want the equivalent Metz flash for the Canon, choose the 44 AF-4 AF TTL.

 2006 Aaron Linsdau

Nikon SB-80DX flash unit measures 4.69V on the X-sync contact

Nikon's older advanced flash, SB-80DX, is voltage compatible with all modern digital cameras. It only provides D-TTL operation and not the modern i-TTL operation with the Nikon Creative Lighting System (CLS). This flash unit was superseded by the Nikon SB-800.

 2006 Aaron Linsdau

Nikon SB-800 flash unit measures 3.63V on the X-sync contact

A low 3.63V is all that appears on the X-sync contact of Nikon's latest flash gun, the SB-800. This flash unit is the most powerful and advanced available from Nikon offering i-TTL operation and is the centerpiece of the CLS. Obviously this flash is safe for use on all modern digital cameras.

Conclusion
Several of the older flashes measured would likely damage a modern digital SLR camera and are not suggested for use. Also, all older flashes do not offer the flexibility and advanced metering capability of the modern flash heads. Even Nikon's SB-80DX flash is reduced to Automatic A mode and manual power settings when used with the current batch of digital SLRs, a shame for a $330 piece of equipment. Purchasing the new SB-600 or SB-800 from Nikon or the Canon Speedlight 580EX or 430EX will give you the maximum capability of either system.