Expose to the Left: How to Really Maximize Image Quality at Night
We hear everyone in the photography industry talking about image quality, image quality, image quality. We especially hear about this in any circle of people chatting (or writing) about night photography. Conversations (and books, articles and blog posts) are rife with opinions and advice about how to push the limits of our cameras and lenses in order to get the best image quality in low-light situations.
But at what cost? We get so caught up in capturing all this dim light that we don’t notice that we’re making decisions that in every other photography situation are actually detrimental to image quality:
- Opening the aperture as wide as it will go
- Leaving the shutter open for long periods of time
- Jacking up the ISO to numbers far beyond what the photographers of yesteryear would even believe as factual
Ideally, night photographers need to be thinking the other way around: How do we improve our low-light photos in a way that capitalizes on everything we know about shooting in daylight? The answer is straightforward, and it all boils down to shooting with this philosophy, with this technique: Expose To The Left, otherwise known as ETTL.
What is ETTL?
Like its fraternal twin ETTR (Expose To The Right), ETTL is a way to maximize image quality, except while ETTR is used in daylight, ETTL is used at night.
How does it work? It’s simple. With your camera set to Matrix metering, shoot a test exposure that’s probably a couple of stops darker than the meter reading. You can just guess—accuracy doesn’t matter, kind of like with print film. Looking at your histogram, adjust the exposure downward and keep firing test frames until all the data is crammed up against the left side, or the “shady side,” of the graph. We push that histogram over by using a smaller aperture, a faster shutter speed, a lower ISO.
A perfect example is a photo I made in Gates of the Arctic National Park, of the wingless bats that live in Inverted Canyon. I was shooting under a new moon. My first-guess exposure was 20 seconds, f/2.8, ISO 6400, which resulted in a rather “traditional” histogram, as seen in Figure 1.
But I didn’t want traditional—I wanted ETTL and all the advantages that come with it. So I closed down the aperture to f/5.6 and dropped the ISO to 1600. That gave me a better ETTL histogram (Figure 2), but still not good enough.
So I cut another two stops of light by dropping my ISO again, to 800, and increasing the shutter speed to 10 seconds. The resulting histogram (Figure 3) was certainly close—close enough to be effective, in fact. But it resulted in what I call a “Thick Shady” histogram, wherein you can see that all the image data is pushed to the left, but you can still make out a slope of data curving up on that left side. By increasing my shutter speed to 2 seconds, I was able to narrow that to a slim line of histogram data (Figure 4)—or what’s known as “Slim Shady.”
What did I gain by doing this? Consider my initial, traditional-histogram exposure of 20 seconds, f/2.8, ISO 6400:
- That 20 seconds introduced long-exposure noise.
- That f/2.8 gave me paper-thin depth of field.
- That ISO gave me high ISO noise.
All of which are bad for image quality.
However, my ETTL exposure was 2 seconds, f/5.6, ISO 800, which fixed every one of the dire consequences of that first exposure. You can see how sharp the final image is in Figure 5; no long-exposure noise, adequate depth of field, no high ISO noise. Moreover, f/5.6 is the sharpest aperture for the Nikon lens I was using, which further improved the final image. Click/tap to see the photo at full size. Not a blurry pixel in sight. Not a spot of noise. The image quality is perfect.
Ancillary Advantages of ETTL
In addition to image quality, ETTL has other advantages.
As crazy as it sounds, you can “freeze” action even in the dark. Because you’re not worried about all the tedious challenges of maintaining highlights, midtones and shadow details, you can manipulate your shutter speed to almost anything you want. For example, while doing a night shoot at Upward Falls in North Cascades National Park, I didn’t want motion blur in the water. But because I was using ETTL, I was able to shoot at 1/60, f/4.5, ISO 2000. Subsequently, I got great image quality while freezing the action of the falls (Figure 6) despite the low light.
Another side benefit of ETTL is that you can hand-hold your camera when making night images. Even under the new moon! Because you can shoot at those higher shutter speeds, you don’t really need to carry a tripod into the field with you.
Drawbacks of ETTL
As great as ETTL is for improving image quality in night photography, there are some obstacles to work around.
For one, this exposure technique gets trickier when you’re light painting. It’s especially troubleshome when you’re using a sunbeam-like flashlight such as the Coast HP7R, because it completely ruins your hard-achieved left-biased exposure. How? By adding light. But don’t fret—there’s an easy solution.
If you’re using ETTL to determine exposure for a scene you need to light-paint, then get a snoot that fits onto the end of your flashlight, such as the Universal Connector made by Light Painting Brushes. Cover the far opening of your flashlight with a thick and subsequently expensive layering of gaffer’s tape (Figure 7, above). With this modified snoot on your flashlight, you won’t impair your ETTL exposure. This is exactly what I did to light-paint a night wildlife scene in Voyageurs National Park (Figure 8).
Another option is to apply a thick layer of black paint over the front of the flashlight lens. Just be sure to use removable paint, so you can peel it off, lest you have to head back down the trail in the dark.
Along the same lines, a strobe is even more detrimental to ETTL, because even though that light burst comes and goes in a flash, it’s really bright. For this situation, I suggest foraging your closet for the case your strobe came in when you bought it. Then put the strobe in that case before firing it. Even better, see if you can buy an extra case and put the flash in both. Extras are pretty easy to find on eBay. (Well, maybe not now that I’m sharing this tip.)
Lastly, pixel-peepers will notice that the ETTL approach diminishes highlights a bit. But don’t worry about it. Just like Meghan Trainor sings in her catchy pop song—“It’s all about that bass, about that bass, no treble”—it’s similar for night photography. It’s all about the shadows, about the shadows, no highlights. After all, night photography is all about photographing within the biggest shadow in the whole world. Seize the shadow.
A Final Note on ETTL
Some photographers accomplish the ETTL effect solely in post-production. In other words, they photograph the scene with a “traditional” exposure. Then they import the photo to Lightroom, pull the Exposure slider all the way to the left, and then reduce the Shadows setting a tad. But the effect just isn’t the same. Get it right in-camera.
I suspect that the ETTL technique will be new to many people reading this, but I promise two things: 1) It will result in better image quality in your night photos. 2) It’s easy to learn, and fun!
If you decide to experiment with ETTL, please do come back and share your results in the Comments section.
About the author: Chris Nicholson is the author of Photographing National Parks (Sidelight Books, 2015). Learn more about national parks as photography destinations at the Photographing National Parks website. This article was also published here.