Why does my flash fire when the PC sync plug touches the socket, but not when I press the shutter?
Asked 11/22/2017
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2 answers
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I connected an AmazonBasics flash to my camera with a PC sync cable. As soon as the plug touches the flash’s PC sync socket, the flash fires, and if the cable moves slightly it may fire repeatedly. But when I press the camera’s shutter, the flash does not fire.
The camera is a manual-only SLR. Is this behavior normal, and is the problem more likely the cable, the flash PC port, or the camera connection?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
1
Everything you are describing sounds like the cable you are using has an intermittent short in it.
It could also be a simple case of not having the cable properly plugged all of the way in either at the camera or at the flash.
The way flashes work is that the power to trigger the flash comes from the flash. The main pin on the camera's hot shoe is only a switch that shorts the ground (the rails on the side of the hot shoe) to the center pin so that the energy from the flash is allowed to return to the flash on the other side of the cable's polarity. The same is true of the camera's PC connector. When the shutter fires a short is created between the center pin and the outer ground that allows the energy from the flash to flow through it and back to the flash.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
8y ago
0
Generated from our catalog & community — verify before relying on it.
A flash firing when the PC sync plug touches the contact is normal or at least not unusual. PC sync works by briefly shorting the center contact to ground; simply touching or moving the connector can create that trigger, so it’s best to connect it with the flash powered off.
The bigger issue is that the flash does not fire from the shutter. Based on the answers, the most likely causes are:
- an intermittent short or fault in the PC cable
- the cable not being fully seated at the camera or flash
- less likely, a camera setting or shooting mode that disables flash triggering
Since moving the cable causes repeated firing, the cable is especially suspicious. Try firmly reseating both ends and testing with another PC sync cable if possible. If your camera has exposure or scene modes that suppress flash, switch to a mode that should allow flash sync. On a manual SLR, the cable or connection is the most likely problem.
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