When photographing grand landscapes that include the sky, the contrast range between the darkest area and the lightest area that you want to capture detail often exceeds what film or digital sensors can capture. Color film has a dynamic range of about 5 stops, but high contrast situations found in the early morning and late in the day often have a dynamic range of more than 7 stops. As a result, you need some way to reduce the contrast so that you don't burn out the highlights and lose detail in the shadows.

The traditional solution used by many photographers is to use a graduated or split (ND) neutral density filter to reduce the contrast of the scene to a range film can capture. The dark section of the ND filter is placed over the bright sky, allowing you to expose for detail in the foreground. One problem with this method is that it takes time to set up because you have to determine the dynamic range of the scene using a light meter, figure out what stop ND filter to use and then mount and adjust the filter on the lens. Having to do all this takes time and may result in missed opportunities because of the fast changing light late in the day and early morning. Another problem encountered is that horizons are not always straight. Often times you have mountain peaks, trees and ridges that make it difficult to ND filter properly.

Blending Solution

Shooting Method
When shooting a high contrast scene with a digital camera, I first must determine if there is any type of movement in my scene, such as boats or vegetation moving in the wind. Otherwise, you may find some ghosting in the blended image. If there is movement in scene, I'm forced to use one shot and then over/under expose the image when I convert it from RAW to a TIFF file. In this case, I try to expose the shot so that the histogram is as close to the right edge as possible without burning out the highlights using a technique I learned from luminous-landscape.com (See Expose to the Right). If there is no movement in the scene, I shoot several different exposures using Apeture Priorty so that I have at least one image that captures detail in the shadows and one that properly exposes the sky. Make sure that you switch to manual focus before shooting so that the focus point is the same of all images. Obviously, you should use a tripod to have success with this method.

Photoshop Method
I didn't invent this method and don't remember exactly how I learned it, but I modified it slightly and simplified it for my use. The procedure below was done using Photoshop version 7 in Windows.

1. You must first save the underexposed and overexposed images to a TIFF file and then open each with Photoshop.

2. Convert both images to 8-bit using Image/Mode/ 8-Bits Channel.

3. Select the Move Tool from tools palette.

4. Press and hold the shift key and then use Move Tool to drag the overexposed image on to the underexposed image. Both images should now be exactly aligned.

5. Close the overexposed image file because you'll only be using the underexposed image file.

6. Select the layers palette and you should see both layers.

7. With the overexposed layer highlighted, select the Add vector mask button on the lower left of the Layers palette and a white layer box appears.

8. Select the Gradient Tool from the Tools palette and drag it from just below the horizon to the top of the image. Notice how the sky now looks properly exposed and the foreground has detail.

That's it. You can play with Opacity level if you feel you need to darken the image. Also, before you apply any sharpening and prior to printing, flatten the layers by using Layers/Flatten Image. Good luck!