Can you defend your exposure settings?

Posted on July 15, 2016

Gary Hart Photography: Floating Dogwood, Merced River, Yosemite

Dogwood Above the Merced River, Near Fern Spring, Yosemite
Sony a7R II
Tamron 150-600, Canon-mount with Metabones IV adapter
1/125 second
F/8
ISO 1600

While I’m a huge advocate of manual metering (it’s all I’ve ever used), I stop short of saying everyone shoot shoot in manual mode. But I do believe that anyone who is serious about their photography should at least be comfortable shooting in manual mode. That means understanding how a light meter “sees” a scene, the information the meter returns, and how each of the camera’s three exposure variables affect an image. (I won’t get into the rudiments of metering now, but you can brush up here: Exposure basics.)

We have three ways to control the amount of light our sensor records:

Aperture, measured in f-stops, is the size of the opening that allows the light in. Controlling exposure by changing the aperture affects your depth of field—larger aperture (smaller f-stop), means less depth of field.
Shutter speed is how long the light strikes the sensor. Controlling exposure by changing the shutter speed affects the way the camera captures motion—a faster shutter speed freezes motion, a longer shutter speed blurs motion.
ISO is the sensor’s sensitivity to light. Controlling your exposure by adjusting the ISO affect the digital noise in the image—increasing the ISO to make the sensor more sensitive to light increase’s the resulting image’s noise.

Every image you capture uses a combination of these three variables to establish the exposure (amount of light) for every image. And because the variable you choose to adjust affects more than just the exposure of your image, if you can’t justify your choice for each of the three exposure settings for every shot (if it’s not a conscious decision), you have a wonderful opportunity to improve.

To illustrate, I’ll explain my exposure choices in the dogwood image above (a new image, captured during my 2016 Yosemite Moonbow and Wildflowers workshop in April). Though I used f/8, 1/125 second, and ISO 1600 to achieve my desired exposure, keep in mind that I could have achieved exactly the same exposure by choosing f16, 1/4 second, and ISO 100. Or f5.6, 1/500, and ISO 6400. Or a virtually unlimited variety of other combinations that all would have captured the same amount of light. But since whatever exposure combination I decide on will potentially yield a completely different image (different depth, different motion, different noise), I had to be very careful with my decisions.

So here goes:

f/8: Because the f-stop determines the depth of field for my chosen focal length and focus point, and I try to compose with front-to-back relationships in every frame, f-stop is usually my primary, non-negotiable exposure variable. In this case I wanted my background soft to force my viewers’ eyes to the dogwood only, but not so soft that the background whitewater was unrecognizable. I decided that f/8 gave me the right balance of foreground sharpness and background softness.
1/125 second: When photographing a stationary landscape on a tripod, I can go with whatever shutter speed I need, but when there’s motion in the scene, my shutter speed becomes as important as my f-stop. On this afternoon, in addition to the water moving in the background, I was dealing with a slight breeze. If the breeze hadn’t been a consideration I could have chosen whatever shutter speed gave me the best motion effect, but I needed to freeze the swaying dogwood and was confident I could do that at 1/125 second.
ISO 1600: Because it gives me the cleanest images, I always go with ISO 100 when possible, but that wasn’t an option here. Given that I needed f/8 for my desired depth of field, and I wasn’t comfortable keeping my shutter open longer than 1/125 second, ISO was the only remaining variable to control the light in my scene. I spot-metered on the brightest dogwood and increased the ISO until my meter indicated the flower was as bright as I could make it without overexposing. The dynamic range in this scene was great enough that even though the dogwood bloom was fully exposed, the shadows remained quite dark, but fortunately that helps the dogwood stand out.

This was my process and rationale for this image. Depending on the factors I’m dealing with, my process might follow a completely different path for another image.

In general I tell people just learning to master manual metering to approach every scene with a tripod (non-negotiable—with no tripod, my suggestions below aren’t valid) and this mindset:

F-stop: f/11, because this provides the most depth of field possible at an f/stop that is in most lens’s sharpest range, and without significant diffraction.
ISO: 100 (or whatever your camera’s native ISO is), because this is where you’ll get your cleanest (least noise) images.
Shutter speed: Adjust until you’ve achieved the proper exposure.

These guidelines certainly don’t apply to all situations, but they’re a good starting point that will simplify the decision making process until you get more comfortable juggling your exposure variables. And keep in mind that you’ll need to deviate from f/11 and ISO 100 whenever your creative needs and the scene conditions (such as wind or moving water) dictate. Practice makes perfect.