If you try to find any information on the relationship between shutter speeds and flash, you’re likely gonna find a lot of articles on high-speed sync and things of that sort. One thing that isn’t talked about as often is what happens when you slow that shutter speed down. While it’s not the method for every photo, it’s one tool to have in your arsenal that can help you create the photo you’re trying to make!
To demonstrate this, I made a simple setup at home that would show the results very clearly. I had my wife sitting at our dining room table, turned off the lights, but put a table lamp right next to her and turned it on. The only continuous light source in the room was the table lamp. I had a flash set up in a softbox to my left and set my exposure for the flash.
I was shooting with a Leica M 262 and a 50mm Summicron. I set my aperture to f/2, my ISO to 200, and the flash power was at 1/16th. None of those settings changed during this entire demonstration. The only thing I adjusted was the shutter speed, which started out at 1/180, the fastest sync speed of the Leica M 262. From there, I slowed down my shutter over and over to show incremental changes.
What happens when the shutter is open for a longer time is the light from the lamp begins to become more apparent. The exposure of the flash doesn’t change because it isn’t continuous light and the aperture is what you’re using to expose for the flash. Because those two things didn’t change, the value of the flash stayed the same. The shutter speed only affects the continuous light in your scene.
You can see in the example photos going from 1/180 to 1/15, you get a huge change in the feel of the image. It’s a simple step, but something to keep in mind next time you’re working with flash and want to change up your results!
The KEH team would like to thank Matt Day for creating this blog entry. To view more of Matt's videos, please visit Matt Day's Youtube channel