Over the past few years, I have transitioned from a DSLR (Canon 1Dx) to a mirrorless camera (Canon R, now R5). One of the things I have noticed with the change is the simulated exposure that is available with the mirrorless cameras. This is an a way a step up from the live view that was possible with some DSLRs, but there are some differences. First, what you see on the back of the LCD or in the viewfinder on a mirrorless camera is always simulated. Sometimes, the camera will simulate and brighten the image to look fine even though the exposure settings are completely wrong. I have tried to use the histogram on the image, but I found the results less than optimal.
There is a second challenge with long exposure — ND filters and the stark change in exposure between the filtered view and the view with the ND removed make it hard to predict what you will see on the live view. Switching between the filtered and unfiltered image runs the risk of nudging your circular polarize or shifting the focus as you switch the filter on and off. For me, I always relied on the meter reading in the unfiltered image as the base exposure and would adjust the shutter speed with the aid of a ND lookup table or app. With the R5, I noticed I was consistently “botching” my exposure with the ND filter, so I thought about solutions. I have the perfect solution — a light meter!
I don’t know why I never considered a light meter before. There are smartphone apps that do a good job so everyone can have one. I have a Sekonic 308X light meter from when I was experimenting with by grandfather’s Leica M3. It was essentially collecting dust while I was struggling to get the exposure right. This is a problem when using a 15 stop ND as even middle of the day photos can take 4+ minutes. That’s a lot of waiting around to be disappointed while your sensor heats up.
My new recommended workflow is this.
As you set up your tripod, get a basic meter reading with the light meter to see what type of ISO is going to be required for you base shutter speed and aperture. I typically want an F/8 or F/11 for the long exposure, so that tends to be fixed. I generally want a base shutter speed in the 1/125 range to give up to a 4 minute exposure with a 15 stop ND. I do all of this tinkering before I start mounting the filters.
Focus and compose using the circular polarizer. Adjust the polarizer to give the sky or water character you are going for. Verify the exposure settings locking in the F stop and ISO. I will general take a test shot (and set the 2 second timer) and inspect the image. Once satisfied, I apply the ND filter and program in the F stop and ISO into the light meter.
Using the light meter, take a few meter readings for the photo. The light meter should be set to estimate the exposure based on shutter speed (i.e., assume the F stop and ISO are fixed and let the shutter speed be the variable that changes), calculate the lengthened exposure due to the ND using any number of ND calculator apps or look up tables.
If you have a modern camera, there should be a bulb mode with an option in the menu to set the shutter time. Dial in what your app suggests. Otherwise, a remote trigger can be used to time the exposure.
Start the capture. It is likely a good idea to use the 2 second timer for the exposure but depending on how long the exposure is, this doesn’t have a major impact on the final image, even with high resolution cameras. Still, the timer is the best option but if you forgot to use it, don’t worry too much.
Enjoy the perfect exposure! Sort of, there are times that light changes over the long exposure so this can affect results. If there is a chance of this, you may want to underexpose the image when you set the timer (again, apps make this simple to do).
Resulting image — one single exposure. This image is straight from the camera with the B&W 09 Lightroom color profile applied to it. Getting the exposure right in a single take saved me at least 4 minutes. In this case, it started raining 5 mins after this photo. A retake would have prevented me from capturing a different composition.
Final Image - f/5.6, ISO 200, 262 seconds, 35mm, Canon R5.