(This is a slightly modified version of something I wrote as part of a discussion on Google+)

The author of the post that I read before writing this mentions two alternatives for dealing with dynamic range issues in landscape scenes – the use of graduated neutral density (GND) filters or the use of a similarly-named post process technique in Lightroom. (Similar processes are available in other software including Photoshop/ACR.) Another alternative is to use HDR (High Dynamic Range) techniques that allow computer algorithms to combine source images in ways that are not the same as what I describe in this post. I almost always use a different approach, exposure blending, and I’d like to share a few ideas on this topic.

When the scene contains an extremely large dynamic range – a common situation in landscape photography – it is possible to end up with shadow areas that are nearly black and devoid of detail, along with bright areas that are blown out and also completely lack detail. (The latter is especially an issue with digital capture in which overexposed areas can simply become pure white. Film failed more gracefully in this situation.)

One traditional method for dealing with such scenes is to attach various types of graduated neutral density (GND) filters to the front of the lens. These filters include a clear area and an area darkened by a few stops. A typical use might be to position the dark portion over the sky and the clear section over a darker foreground, effectively reducing the dynamic range of the light reaching the sensor by reducing only the brightness of the sky. With film, especially positive transparency film, this was just about the only realistic way to handle the situation in many cases.

A second method is to make a single exposure and use features in Photoshop/ACR, Lightroom, or other software to simulate the effect of the GND, lightening (or darkening) a portion of the photograph. This can often help quite a bit when it comes to balancing out dark and light areas in the image, and the fact is that most savvy landscape photographers do this sort of thing and more in post. But it has its limits. For example, darkening a bright area cannot put detail back in blown out areas, and lightening underexposed shadows can lead to problems with noise and posterization. The bottom line is that this technique works well when the overall range 0f brightness in the scene does not exceed the dynamic range of the camera – here it may be used to adjust the relative levels of the areas – but it does not work well when the dynamic range is actually too great for a single normal exposure.

There is a third method, sometimes called exposure blending, that can often be used when making the exposure. The idea is to make more than one exposure, with each exposure optimized for different parts of the scene by varying shutter speed, and then selectively blend the two exposures during post-production.* Two exposures are sufficient in almost all cases, with one for the shadow detail and the other for highlight detail – though in very complex or wide dynamic range situations more exposures can be used.