Every so often I’ll be outside at night and see some interesting clouds passing in front of the moon. This can be quite a beautiful sight, especially with a pattern of small, puffy clouds stretching across the sky. And under these conditions you can often see a rainbow-like corona around the moon.
I’ve tried to photograph moonlit clouds like this a few times, with mixed results. Usually by the time I get out my camera, find a suitable viewpoint, compose, focus, and figure out an exposure, the clouds are gone – or at least less interesting.
About a week ago Claudia and I saw some beautifully-patterned clouds floating by the just-past-full moon, and I decided to try again. I took my camera out to an open meadow near our house, but by that time, sure enough, the clouds had changed, and weren’t as interesting.
I decided to try anyway, starting with a wide-angle lens. Then the beautifully-patterned clouds returned. I thought I needed a tighter view that made the moon and corona more prominent, so I switched to my 70-200mm zoom at 70mm.
I wanted to get detail in the moon, as well as the clouds, and the difference in brightness between the two was extreme. Imagine trying to get detail in the sun itself, and also in clouds lit by the sun. It’s the same contrast ratio between the moon and clouds, or between any light source and something lit by that light source.
Given all that contrast, it was essential to bracket and blend exposures in order to retain detail in both the moon and the clouds. If I tried to use just one exposure, and made that exposure dark enough to retain detail in the moon, I’d then have to lighten the rest of the photo so much I’d get tons of noise.
Lightening an image (or part of an image) in software is equivalent to increasing the ISO. They’re both ways of amplifying the light signal reaching the sensor. Amplifying that signal creates noise; amplifying that signal a lot creates a lot of noise. (You’ll generally get less noise by increasing the ISO in the camera rather than lightening the image later, but that difference is slight with some cameras, such as those with Sony sensors.)
So bracketing and blending exposures is actually a way to reduce noise in high-contrast scenes. Instead of making one exposure dark enough to retain highlight detail, and then lightening the rest of the image in software (which amplifies the signal and brings out noise), you can blend that dark exposure with some brighter ones – made brighter by actually increasing the light reaching the sensor with a longer exposure or a wider aperture, rather than by amplifying the signal. Those lighter frames won’t have to be lightened and amplified to bring out shadow detail, since they’re brighter to begin with, so you’ll end up with less noise in the darker sections of the photo.
In this situation, bracketing was complicated by the fact that the clouds were moving rather quickly. If there was too much movement the clouds wouldn’t line up in the different frames, leading to ghosting if I blended the exposures using HDR software. But I knew bracketing was essential, and reasoned that I could always blend the exposures by hand in Photoshop, which should eliminate any ghosting.
In order to minimize the time between exposures, and lessen the ghosting, I used auto-bracketing, with three frames two stops apart. The middle exposure was 1/3 sec. at f/5.6, ISO 800. That made the darkest exposure 1/10 sec., and the lightest 1.5 seconds. The darkest exposure (1/10 sec.) was just dark enough to get detail in the moon – at least when the moon was slightly dimmed by passing clouds. (Using a lower ISO would have required slower shutter speeds, and risk blurring the clouds or increasing ghosting, or both.)
All of this might sound complicated, but those calculations were second nature to me – almost instinctive. That comes from experience, and spending a lot of time behind the camera making similar decisions.
In the end, Lightroom’s HDR Merge worked fine, with no ghosting, so blending the exposures was easy. And I liked some of the resulting images more, I think, than any of my previous attempts at photographing moon-and-cloud scenes. It was nice to capture something that conveyed – at least a little bit – of what it looks and feels like to view those beautiful, moonlit clouds.
— Michael Frye
P.S. There’s still time to sign up for the Night Photo Summit next weekend, where I’ll be giving a presentation called Noise-Reduction Strategies for Night Photography. I’ll be joining a long list of wonderful night photographers and instructors for this online conference – people like Lance Keimig, Tim Cooper, Adam Woodworth, Jess Santos, Chris Nicholson, Rachel Jones Ross, Troy Paiva, and many more. You can learn more and sign up here:
Michael Frye is a professional photographer specializing in landscapes and nature. He is the author or principal photographer of The Photographer’s Guide to Yosemite, Yosemite Meditations, Yosemite Meditations for Women, Yosemite Meditations for Adventurers, and Digital Landscape Photography: In the Footsteps of Ansel Adams and the Great Masters. He has also written three eBooks: Light & Land: Landscapes in the Digital Darkroom, Exposure for Outdoor Photography, and Landscapes in Lightroom: The Essential Step-by-Step Guide. Michael has written numerous magazine articles on the art and technique of photography, and his images have been published in over thirty countries around the world. Michael has lived either in or near Yosemite National Park since 1983, currently residing just outside the park in Mariposa, California.