Taking differently exposed images
Here are general recommendations for taking a High Dynamic Range scene under different exposure settings. The calculation for the number of exposures is based on a spacing of two EVs (Exposure Values) between the exposures. You will need to adapt if you are using a different EV spacing.
We recommend a spacing of 1.5 to 2 EVs between the exposures, as lower EV spacings require more exposures to capture the same dynamic range, which increases the risk of mis-registration and ghosting issues. However, a lower spacing can be used to reduce noise in the resulting HDR image.
A spacing of two EVs between the images means that the exposure time of one photo will be four times higher or four times lower than the exposure time of the next exposure in the sequence. For instance, if the photo at the middle exposure is taken at 1/15 second, an EV-spacing of two means that the overexposed photo will be taken at 1/4 second and the underexposed one at 1/60 second.
1. | Mount your camera on a tripod. Though Photomatix includes a feature to align hand-held images, using a tripod is still highly recommended.
2. | Set your camera to manual exposure mode. Select an appropriate aperture for your scene, e.g. f/8 or less (i.e. higher f number) if you need more depth of field. Select the lowest ISO setting, unless your scene includes moving objects.
3. | Measure the light in the brightest part of your scene (spot metering or in Av mode to point only the highlights) and note the exposure time. Do the same for the shadows of your scene where you want to see details in.
4. | Determine the number and value of exposures necessary. For this, take as a basis the exposure time measured for the highlights. If you are using an EV-spacing of two, multiply this number by 4 to find the next exposure time. Multiply by 4 successively for the next exposures till you pass the exposure time measured for the shadows. (Note: For most scenes, 3-4 images should be sufficient to cover the dynamic range).
5. | You can make use of auto-exposure bracketing if your camera supports it and if it allows taking 3 bracketed frames at 2 EV, or 5 bracketed frames at 1 EV. Otherwise (for instance if your camera can only autobracket 3 frames at 0.7 EV), you will need to vary the exposure times manually.

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