Use a Light Meter to Bracket in HDR
Using a preconceived bracketing strategy in high dynamic range (HDR) photography works well, but the downside is not knowing whether you’re really capturing the full dynamic range of the scene with the brackets (if you pay attention to a live histogram, you’re closer to knowing).
A more studious approach relies on metering highs and lows in the scene with a light meter to come up with a more reliable estimate of how many brackets you should shoot.
This strategy is not as accessible if you use exposure compensation. Most cameras limit the total EV compensation exposure range from -2.0 to +2.0 EV. Therefore, it’s important to have a camera with a manual shooting mode for this method.
Using an external light meter takes a bit more time and preparation than setting up your camera and shooting normal brackets, not to mention the fact that you have to purchase a light meter with a spot mode. After the metering and figuring are done, however, you’ll shoot the photos much like manual bracketing.
Follow these steps to use the alternate metering strategy with a light meter:
Set up your light meter.
Keep the aperture constant by using aperture priority mode on your light meter. Set ISO and aperture to the same as your camera.
These examples use ISO 100 and the aperture of f/8. Changing these settings won’t materially affect how you shoot anything — as long as you’re consistent within a bracketed set.
This figure shows a light meter. The white thing at the top — a Lumisphere — is used to measure incident (as opposed to reflected) light. Incident mode is used to get an average exposure and set the shutter speed for 0.0 EV.
Use spot mode to meter the lows and highs. For this meter, you must look through the eyepiece on the right and out the spot lens to the left, which you aim at the location you want to measure.
Please refer to your light meter manual for the specifics on how to configure and use your light meter.
Set up your camera for manual bracketing.
Compose the scene.
Meter a highlight with your external light meter.
This figure illustrates putting the spot circle of the light meter on a bright spot in the scene while taking a measurement. In this case, the bright front end on the car works well. You can take a few different measurements of various areas of the scene (the sky, chrome, and so on) and choose the brightest one.
Make a note of the shutter speed. This is where the high bracket is shot. In this case, it’s 1/1000 second.
Meter a shadow with the light meter.
This figure shows the meter looking at a dark area of the scene. Make a note of the reading. In this case, the shutter speed is 1/4 second.
Take an average light reading.
Switch to Incident mode on your light meter and take an average reading of the scene. You can also use your camera for this, even when mounted on a tripod.
This measures the overall exposure and gives you the shutter speed necessary to set exposure to 0.0 EV value. Make a note of the shutter speed. In this case, the reading is 1/60 second for 0.0 EV.
Calculate the points at which you want to bracket.
You have now measured three data points and have three shutter speeds to show for it. You have the low and high points of the scene from Spot mode and the 0.0 EV point by using the Luminance mode (or your camera).
Using this information, decide on a bracketing strategy. Notice that the low bracket is at -4.0 EV and the correct shutter speed is 1/1000 second. This is where you set the camera for the first shot. Afterward, each bracket is incremented by +2.0 EV (shutter speeds are also shown) until the high point is also photographed.
In this case, it’s nice — although not always the case — that the low and high points are at +/-4.0 EV, respectively, and that there is an even +/-2.0 EV difference that connects them.
In situations where the figures aren’t as evenly spread, start at 0.0 EV and measure outward in both directions the number of EV you need to shoot to include the high and low values. It’s okay to go past them — but you don’t want to come up short.