High Dynamic Range Photography
High Dynamic Range (HDR) photography is a technique for having a wider tonal range in photographs.
When, for example, a photograph is being taken of a landscape, a digital camera does not have the ability to record both the shadow areas, like beneath trees, as well as highlight areas, like the sky, perfectly in the same photograph. The sky is over exposed and the shadow areas are under exposed making the photograph, as a whole, properly exposed. If the same photograph is over exposed by two stops then the shadow areas show greater detail and if under exposed by two stops then the sky shows greater detail.
The human eye has a very high range and HDR images tend to look more like what we remember seeing.
In HDR photography, we can take three photographs: one exposed at the regular, or middle value as set by the camera's meter (0 EV; 0 Exposure Value), one over exposed by two stops (+2 EV) to capture detail in the shadow areas, and one under exposed by two stops (-2 EV) to capture detail in the highlight areas. These three photographs are then combined into one either within the camera itself or with special HDR aware software applications. These applications understand how to use the detail from the shadow areas of the over exposed photograph and the detail from the highlight areas of the under exposed photograph to make an HDR image. For an even greater effect, +3 EV and -3 EV exposures can be taken and then combined. Heavy bracketing and then experimenting with combining them is recommended.
If the camera has a built-in HDR function then it takes care of the bracketing and combining of the photographs. If the camera does not have an HDR function, there are two ways to over and under expose the images. The first is to set the camera in aperture priority mode and then use +2 EV and -2 EV auto exposure bracketing. The second way to over and under expose the images is to use manual mode. If the 0 EV exposed photograph uses a shutter speed of 1/1000 second then the +2 EV exposed photograph will be at 1/250 second and the -2 EV exposed photograph will be at 1/4000 sec. Do not change the aperture as this can change the photographs beyond just their exposure.
The math to figure out the shutter speed is: SHUTTERSPEED × 2EV. So to
demonstrate the math of the previous paragraph:
1/1000 × 2+2 = 1/250
1/1000 × 20 = 1/1000
1/1000 × 2-2 = 1/4000
Now at ±3 EV:
1/1000 × 2+3 = 1/125
1/1000 × 20 = 1/1000
1/1000 × 2-3 = 1/8000
Or simply use the Shutter Speed Calculator.
Finally, if using HDR aware software to combine the photographs, try to shoot in RAW quality mode because the software is usually optimized to work with this format.