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Calculating Exposure with Slower Shutter

I love long exposure photography because it has the power to make even the most mundane scenes a bit more interesting visually. When shooting daytime scenes I often turn to my Lee Big Stopper 10-stop ND filter. The Big Stopper is so dark you can’t actually see through it, which means your cameras internal metering is off the table. Lee does include a small cheat sheet with the filter to help you determine the correct exposure with the ND filter based on the correct exposure without the filter. Unfortunately the cheat sheet doesn’t cover all possible exposure values, so you are left to doing the calculations in your head, just guessing, or using some other calculator. Plus to be honest, I lost that cheat sheet a long time ago.

Granted this isn’t rocket science, but Ive found that more often than not I turn to my smartphone to assist me in more and more of photographic endeavors. There are a few apps out there created specifically to help with ND calculations (check out Nicole S. Youngs article on getting started with long exposure photography for a list of iOS and Android apps). I recently got hold of a copy of Slower Shutter (for iOS only) by Mike Wong and thought Id give it a whirl.

Interface of Slower Shutter
Interface of Slower Shutter

Slower Shutter is a bare bones app that simply does what it says on the tin, which is to calculate the shutter speed required for the number of stops of your ND filter, based on the shutter speed without the ND filter. So to start you simply need to note the shutter speed required for a proper exposure without the filter. In my case I visited a waterfall near my home when the leaves were just starting to change into their fall colors. I found a few leaves on a rock with the waterfall in the background, and I wanted to shoot it fairly wide open to throw the background into softer focus and direct the eye to the leaves. I chose f/4 as my aperture while in aperture priority mode and the camera selected a shutter speed of 1/8.

The shot without the ND filter.
The shot without the ND filter.

I liked the soft background from the shallow depth of field, but I wanted to quiet the stream even more by slowing down the shutter speed with the 10-stop ND filter, so I opened up Slower Shutter and dialed in 1/8 second for my shutter speed and 10 for my ND value, which calculated a shutter speed of 2 minutes 8 seconds with the filter.

Dialing in shutter speed and the number of stops of your ND filter.
Dialing in shutter speed and the number of stops of your ND filter.

To get a 2 minute 8 second exposure I needed to switch from aperture priority to manual mode on my camera. In manual mode I changed the shutter speed to the Bulb setting, which allows me to hold the shutter open as long as I need it to be open. I left the aperture and the ISO (100 in this case) setting alone. This is where Slower Shutter makes itself useful again by acting as a countdown timer. Once you’ve calculated the required shutter speed you tap Set Timer in the app to load that amount of time into the timer.

Load the time into the timer to countdown the duration needed to keep your shutter open.
Load the time into the timer to countdown the duration needed to keep your shutter open.

From there you need to open your shutter at the same time you start the countdown timer in Slower Shutter (just tap the timer). The countdown timer will begin to countdown, and when it reaches the end of the time it vibrates your phone to let you know it is time to close the shutter.

Timer is counting down ...
Timer is counting down …
The 10-stop ND filter really smoothed out the water in the background to make the foreground stand out.
The 10-stop ND filter really smoothed out the water in the background to make the foreground stand out.

I could have made a few educated guesses about the right exposure time using the ND filter, but it was really helpful to have the Slower Shutter app to do that bit of thinking for me. Would it have been better if the Slower Shutter app could control the shutter too? Sure, but there are already plenty of ways to remotely trigger your shutter. This simple app did what it set out to do and saved me a bit of time in the process. Slower Shutter does have some room to grow, and one thing to keep in mind is that the countdown timer doesn’t work in the background if you switch apps.

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