Blending is a photographic technique where one merges 2 exposures of the same scene to make a singular image. A tripod is needed as the two shots of the scene need to be identical.
I found this a useful technique to use when I was shooting a landscape that had a lot of contrast in the scene that I wanted to photograph. It was an overcast day, so the sky was a bright grey and the foliage around was dark in colour due to the rain that had just fallen. As my camera’s dynamic range is pretty standard, I found myself at odds with how I was going to capture this scene. Would I expose to get details in the shadow areas, like the foliage (which would cause the main highlight area – the sky – to blowout and loose any detail in the clouds, or expose for the sky and risk loosing detail in the foliage? A hard question for me, as both parts are equally needed in my frame.
This is where blending exposures worked and enabled me to keep detail in both the shadow and highlight areas.
Underexposing by two stops, I used this exposure to capture the dark details of the sky in order to bring out the overcast look of the scene. I then took a new exposure of at least 1 stop above what the light meter read as the correct exposure for the scene. This exposure would be used to lighten the foliage and bring out its detail.
In photoshop, I placed the darker image on top of the lighter one. By using the ‘mask brush”, I painted in the bottom 3rd of my frame. By using the mask tool, this meant that I could mask out the darker exposure, therefore bringing out the lighter exposure from beneath it.
Is this process completely necessary? One can do all this – without having to take two exposures of the same scene – by lifting the ‘shadow’ slider in Lightroom 4 in order to retrieve detail, and lower the highlight slider to get detail in the highlight areas of the image.
My problem with this though is that sometimes detail cannot be retrieved. If I had to choose whether to have shadow detail or highlight detail, I would have to expose my image accordingly. If my highlights become overexposed, I risk the chance of them blowing-out – which means that there is no retrievable detail. If my shadows become underexposed, I risk loosing detail in them as one cannot retrieve detail in pure black.
The most recent cameras that have been released have greater dynamic ranges than previous models. Greater dynamic range increases the camera’s ability to capture a wider tonal range in the scene at any given exposure.
Ultimately, whether you want to blend exposures or capture the scene in one shot depends on your personal feelings. It is up to you as the photographer to determine the look of your photographs in regards to how you want them to resemble the actual scene and subject you want to capture.