When I set my D7200 to rear-curtain flash, my flashgun fires when the shutter opens as well as when it closes. How can I fix this?
Edward Walker, via email
Jason says… It sounds like you’re using your flashgun in automatic iTTL (intelligent Through The Lens) flash mode. In this case, a pre-flash pulse of light is fired immediately before the exposure. The reflected light is measured through the camera, so that the power of the flashgun’s output can be automatically set for a correct exposure.
The firing of the pre-flash is so close to the actual exposure that you may not notice it in some cases. However, if you’re using rear-curtain flash mode, especially with a slow shutter speed or long exposure, you’ll notice the pre-flash before the shutter opens, then a delay before the main firing of light from the flash just before the shutter closes at the end of the exposure. The pre-flash won’t illuminate your scene, but if you want to stop it firing, you can switch to manual flash mode and adjust the flash power as necessary.
With most flashguns, you can set rear-curtain mode and other flash modes direct from the camera