Don, the 2nd son Loc: Crowded Florida

I put an optical flash trigger (cheap little box thingy) on the Bowens and used the popup flash to trigger the Bowens. No worries.

E.L.. Shapiro Loc: Ottawa, Ontario Canada

Yup! Cheap and dirty- theses little "old school" gadgets have all the built-in electronics to convert any flash unit into an efficient slave- off-camera flash. You just plug them in, find the correct polarity, and fire away. The old Bowans models have a "phone-plug", the Wein has an H plug and there are models that have a PC sync cord terminal. It's easy to make an adaptor. They all work well in indoor and low light situations at reasonable distances. They can be triggered by an onboard Speedlight, a pop-up flash, or any safe studio unit or mono-light that is directly connected to the camera. Theses devices are not affected by high trigger voltages.

No batteries are required- they operate from the trigger voltage. All the solid-state circuitry is enclosed in the housing or imbedded in the plastic. The Wein modes are quite sensitive- they respond to direct and bounced light and some may work out-of-doors once they acclimate to the existing light level. The old one may show up on the used markets- some were called "The Green Dome" or the "Cat's Eye"!

I have half and dozen of them in my kinda junk drawer- they come in handy if I need a quick extra background light or kicker and I run out of radio transmitters. I also use them on industrial jobs- excavation sites where radio transmission are prohibited due to blasting.

TreborLow

I have an old Carrot 680T with 40 volt trigger as measured in the same way as E.L.Shapiro above. I use it with a small SCR slave trigger so it fires whenever it sees a flash. Similar ones available on Amazon for less than $10.
Bob

lamiaceae Loc: San Luis Obispo County, CA

I had one of those too. But it died before I went digital.

Screamin Scott Loc: Marshfield Wi, Baltimore Md, now Dallas Ga

I still have a homemade optical trigger from the early 70’s.

lamiaceae Loc: San Luis Obispo County, CA

Just get a wireless system for your camera and flash or buy a new flash. I have a number of older strobes, some the same brand as my current cameras but I am cautious and isolate the unit from the camera. There is no way I'd try firing my out high voltage battery Metz Stobe though a digital camera. Also I still have a pro Novatron studio lighting system with separate power supply and lamps and long cables. The similar Norman Flashs we had at college sometimes fried the camera contacts back during the 1980s.

PHRubin Loc: Nashville TN USA

I contacted Canon and asked about the voltage limit for the hot shoe. They avoided the subject by saying they don't test competitor's flashes so they won't say. None-the-less, I stand by my previous statement, although that may not apply to a PC sync socket.

TriX Loc: Raleigh, NC

I use an old set of Novatrons with my Canon 5D4. I use the same Yongnuo YN-E3-RT (equivalent of the Canon) RF transmitter that I use to trigger my 600EX-RTs and an inexpensive Yongnuo remote RF receiver (less than $20) with a PC output for the Novatrons. Works like a champ.

amfoto1 Loc: San Jose, Calif. USA

Older flash can have trigger voltage as high as 600 volts! That wasn't a problem back in the days of cameras that were predominantly mechanical. But in the late 1970s and early 1980s cameras started seeing electronics used internally, at first just to control shutter speeds and for metering... but gradually increasing to perform more and more functions.

This became a severe problem as cameras became more electronic... eventually becoming the little computers to capture images we use today! For example, some of the later Canon film cameras and early DSLRs can only tolerate 6 volts. An old 283 with 600V will fry those cameras' circuitry after just a few pops! Other flashes with far less extreme trigger might only do damage over time, with repeated use.

Here is a partial list of flashes and user-measured trigger voltages: http://www.botzilla.com/photo/strobeVolts.html

Here's further description of the problem and how to measure it yourself using an inexpensive, digital Voltage Ohm Meter (VOM, available at Lowes, Home Depot, etc.): http://dpanswers.com/content/genrc_flash_measuretv.php

Around 2004 the International Standards Organization recommended all camera makers insulate their cameras to tolerate trigger voltage of 24V minimum. Both Canon and Nikon far exceeded that by each upgrading their cameras to tolerate 250V. The list of cameras in an earlier response appears to be correct.... basically Canon 10D (2003), 300D (aka Digital Rebel, 2003) and earlier models have a 6V trigger voltage limit. Every Canon DSLR from the 20D (2004) and 350D (aka Rebel XT, 2005) onward is able to handle up to 250V trigger voltage.

The PC sync socket, if the camera has one, has the same trigger voltage tolerance as the hot shoe. (Note: A "PC" socket is a connection normally used for wired triggering a studio strobe system. In this case, "PC" stands for "Prontor-Compur", the manufacturers who first established this standardized type of connector in the 1950s. It does NOT stand for "personal computer" or "politically correct" , in this particular context. For example, a camera's PC socket has no relation at all with a mini-USB socket allowing the camera to be tethered to a personal computer.)

This was Canon USA's Tech Guru Chuck Westfall's statement on the subject in 2007:

"The trigger circuit voltage (TCV) rating for any EOS SLR is the same on the hot shoe as it is on the PC terminal (if the camera has one), but the acceptable TCV level varies according to the camera model. Incidentally, the main reason for the difference is the way the X-sync signal is generated. With the 250V cameras, the X-sync signal is generated electronically. With the 6V cameras, the X-sync signal is generated mechanically. There are no guarantees, but going forward I anticipate that most if not all future EOS SLRs will be safe for TCV up to 250 volts."

A Wein "Safe Sync" is one way to isolate a flash with a high trigger voltage to prevent damage to a camera that can't tolerate it. There are other brands, but any of them will need to be tested. As one response notes, they don't work with all flashes and strobes!

Yes, it's also possible to use an optical slave trigger, such as those shown in earlier posts. The problem with an optical trigger is that anybody else's flash going off nearby will trigger your flash too. They also may not work with all flashes/strobes and might have limited working distance in some lighting conditions.

A wireless transmitter/receiver arrangement is another way to protect your camera from high flash/strobe trigger voltages. HOWEVER, if you go this route you should check that the wireless receiver that will be attached to the flash can handle the voltage. For example, PocketWizard Plus II have a 100V limit, while PocketWizard Plus III have been beefed up to handle as high as 300V without damage.

lamiaceae Loc: San Luis Obispo County, CA

That is pretty much what I have, Chinese RF trigger system. Works with portable flash so yes, I would think it works with my old a/c powered studio strobes. I just have not tried the set up with my digital cameras yet. Would use the Two-prong to PC to the one unit.

domcomm Loc: Denver, CO

I know White Lightning makes a special trigger that prevents studio flash units from overpowering a modern camera.