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Chapter Six: Controlling the Light

Gray Cards at High Noon: Your Camera’s Dynamic Range

For a useful way to test your camera’s dynamic range, you’ll use a stalwart standby—the gray card—to create a multiple-value step chart.¹

Gear: Camera, tripod, gray card and a handheld light meter (optional)

Part One: Gray Card Test

1. Put your gray card on a stand, table or anywhere else it can stay in a fixed position with even, consistent lighting. Grab your camera, put it on a tripod and fill the frame (at least the majority of it) with the gray card.
2. Select an ISO and a middle aperture value—between ƒ/5.6-ƒ/8 is a good starting spot.
3. Turn on Spot meter mode and take a reading from the center of the card, making make sure you’re not casting a shadow, or else use an incident meter. Write this value down as the normal exposure. You’ll want a shutter speed right in the middle of the scale, around 1/125. Adjust your ISO as necessary.²
4. Write out your bracket, using whole shutter stops, going at least 4 stops over and 4 stops under your normal exposure. Starting at the darkest value (the fastest shutter speed), bracket your image in whole stops.
5. Ingest your images into a Lightroom Collection at their default values.
6. Use your eyedropper tool³ (Figure 6A) to evaluate the percentage values (or numeric values, if you’re in a different application than Lightroom). Identify the darkest and brightest images with tone (around 5%—10, 10, 10 in ProPhoto RGB—or less for the darkest image and around 95%—248, 248, 248 in ProPhoto RGB—for the brightest image). Images with values above and below those numbers won’t have much high quality information, if any at all. You may be able to use your processing tools to eke a little out of them in extreme cases.
7. Now count the number of stops above and the number of stops below your normal exposure. Combined, that’s the approximate usable tonal range of your sensor. In Figure 6.22, we counted 7-stops on a Canon 1Dx. This is a rough range; you could repeat the test using 1/3rd-stops to get a more accurate range. Since this isn’t highly scientific testing, whole-stop increments are enough to give us a set of working values. Make a note of how many stops over and under “normal” your camera is capable of capturing.

Bonus: You may want to repeat this test with a different (higher or lower) ISO speed. The amplification used at higher ISOs is known anecdotally to reduce dynamic range in some cameras.

Part Two: High Noon Landscape

This is your chance to be a western landscape photographer. Head out at high noon; you’re going to repeat the dynamic range test out in the real world. The ideal test scene would take place on a clear sunny day at noon.

1. Frame up a shot of rustic barn with deep shadows on one side, a bright metal silo on the other and a clear blue sky. (If that’s not your thing, then just choose any scene that will push the dynamic range of your camera.)
2. Take a Spot meter reading of your gray card and a reference photo at that value.
3. Now, compose your landscape photo, including the areas with the deepest shadows and the brightest diffuse highlights. Take a shot of the landscape at your Spot meter reading.
4. Find the brightest and darkest areas in your scene, and then take spot meter readings of them.
5. Write these down and compare them to your normal exposure. Count the number of stops beyond “normal” on each side. Is there a smaller, greater or equal range compared to your gray card test in Part One?

 

Compare

Ingest your images into Lightroom at their default values. Put all of the Part One and Part Two images into a Collection for easier organization, and find your gray card reference shots from both parts of the exercise. Using the eyedropper tool, compare the values (percentages in Lightroom, numbers in other applications) and see if they’re the same—they should be fairly close. If they aren’t, then you may need to review your metering and gray card placement.

• Are the dark and bright areas you picked out while photographing (and spot metering) clipped, have a little tone, or a lot of tone?
• Do you seem to have more, equal, or less tonal range than you did with your gray card test?

Takeaway

The objective of this exercise is to understand the dynamic range of your camera. In the gray card test, you bracketed to see at what point your camera clips in the shadow tones and highlights. In the landscape part of the exercise, you compared your spot-metered values to see if they fell inside or outside the dynamic range you tested with the gray card.

With this information, you can determine if your camera will clip or not—and if not, how many stops different the exposures will be from your normal. This knowledge will allow you to adjust your exposure up or down to capture the scene the way you want to. For example, if you wanted to hold texture and detail in the dark tones with a scene like the one in Figure 6.23, you’d take a meter reading of the rocks and decide to expose for them, knowing that your camera wouldn’t be able to hold both sky detail and rock detail.