Why does my Canon 6D change the shutter speed I set in Tv mode with flash?
Asked 10/3/2015
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I’m using a Canon 6D with a 600EX flash. In Tv mode I expected the camera to keep my selected shutter speed as long as it was below flash sync speed. But when I set 1/100s, the camera sometimes records much slower speeds like 1/6s or 1/10s instead. It seems to behave similarly to Av mode with flash, and I’m not sure why the shutter speed I chose is being overridden. What setting could cause this?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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I bet you have enabled safety shift mode, an option which overrides your setting in Tv and Av modes if the result, in combination with ISO and the automatically adjusted parameter, would be severely underexposed or overexposed.
You should be able to disable this; check the camera's manual for how to do it on your particular model. On the Canon 6D, it's in the menu titled C.Fn I: Exposure. It defaults to Disabled, but can be set to Shutter speed / Aperture (as I think yours is) or to ISO speed (which would leave your dialed-in parameter alone but might crank up sensitivity/amplification to prevent all-black frames).
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
10y ago
0
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A likely cause is Canon’s Safety Shift setting.
When Safety Shift is enabled, the camera can override your chosen setting in Tv or Av mode if it thinks the exposure would otherwise be far off. With flash attached, that can mean the camera changes your selected 1/100s to a slower shutter speed such as 1/6s or 1/10s.
On the Canon 6D, check the custom functions under C.Fn I: Exposure for Safety Shift. If it is set to Shutter speed / Aperture, the camera may alter the shutter speed in Tv mode. Setting it to Disabled should stop that behavior. There is also an ISO speed option, which tries to protect exposure by changing ISO instead of your chosen shutter speed/aperture.
So the issue is probably not normal Tv-with-flash behavior itself, but a custom exposure setting overriding your selection.
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