I have been using my dad's old Metz mecablitz 18 B1 flash for a while with my Canon 7D and had no trouble with it, but just received some advice from a friend that using old flashes can fry the camera. Is this true? And if so, is there a safe way to use it (I'm trying to avoid having to buy a new flash – but also would like not to destroy my camera). The flash takes 3 x AA batteries and has a single hotshoe connection.

  • \$\begingroup\$ I think the old film cameras used a mechanical switch to short-cut the contacts of the flashlight. Actually I wonder whether current digital cameras still use a mechanical switch, or some electronics to "short-cut" the contacts. As modern flash lights obviously don't have high voltage on the contacts any more, I guess they have the required electronics (or mechanics) inside to do the conversion. \$\endgroup\$
    – U. Windl
    Nov 12, 2021 at 12:12

3 Answers 3


Yes the trigger voltage on some old flashes is too high for modern electronic cameras.

There is a page on botzilla Photo Strobe Trigger Voltages which lists many old flash units. I don't see your dad's flash model there, but the 20 B3 model had a trigger voltage of 168 volts.

According to "compatibility for 7D and speedlite EZ models?" on photo.net, the 7D can handle up to 250V, so that flash may be safe with your camera, even if it does have a high voltage like the B3 model

There is further information on dpanswers on safe voltages for Canon and Nikon, and also how to measure the trigger voltage of a flash.

  • \$\begingroup\$ Awesome. Thanks mate. I've been using it fairly solidly for a few weeks with no issues so I assume that means it's all good. \$\endgroup\$
    – Chard
    Jan 15, 2012 at 9:09
  • \$\begingroup\$ I think if you've been using the flash for some time it is OK. Otherwise it would burn electronics of your camera during first use. I also had some older Vivitar flash, which I used with my old manual Practica LTL-3, but did not risk using it with my DSLR and bought another one instead. \$\endgroup\$
    – Juhele
    Jan 15, 2012 at 18:31
  • \$\begingroup\$ I have used an ancient flash with my canon 5D MKII several times. Have I damaged my camera? If it has survived so far, does it mean I can keep on using the flash? \$\endgroup\$
    – Pouya
    Jul 4, 2013 at 7:46
  • \$\begingroup\$ @Pouya Measure the trigger voltage ... if it is severely out of spec, yes it can progressively lead to failure. \$\endgroup\$ Oct 9, 2018 at 23:19
  • 1
    \$\begingroup\$ It actually is possible (with care) to measure the trigger voltage on a flash -- you need a voltmeter that can measure at least 600 V (that gives margin to avoid damaging the meter), with the flash powered and "ready" light on, measure voltage from center pin to shoe contact. If that's higher than your camera is rated for, look for a converter or regulator. \$\endgroup\$
    – Zeiss Ikon
    Nov 16, 2021 at 13:31

You can also grab one of these High Voltage Sync Regulators just to be safe:


I think there is also cheaper models as well. Either way they're a lot cheaper than rewiring a camera.

  • \$\begingroup\$ There are the SMDV... models, but they are only rated to 60V... \$\endgroup\$ Oct 9, 2018 at 22:47

Think of the High Voltage Sync Regulators like an isolation bar in between your systems. Like a fuse etc. It does make the flash higher on the camera but ultimately is great insurance against over-voltage issues.

Another option is to use a remote trigger system and use it off-camera. Something like https://www.bhphotovideo.com/c/product/1096382-REG/yongnuo_rf_603ii_c3_rf603_ii_wireless_remote.html/overview

But again with the voltage, I'm not sure what the voltage capacity is of these units and if they are as fragile as the camera body.

  • \$\begingroup\$ OTOH, the sync voltage limit of the RF-603 (Mark I) was only 12V. Just saying. Not all triggers are going to act as voltage/limiters. \$\endgroup\$
    – inkista
    Nov 18, 2021 at 22:23

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