A friend recently asked me if the old adage of “expose to the right” still holds true for Night Photography. It’s a good question, and seemed like a good topic for a blog post.
Different types of night photography require different exposure strategies. For astro-landscape photography, try to get the histogram off of the left side of the frame- just a gap between the left edge and shadow portion of the histogram. You have to push the camera to the threshold of its capabilities, so that’s about the best you can hope for. At high ISO, maximum aperture, and shutter speed limited by apparent stellar movement, a right-biased histogram is not a reality. Fortunately, an increasing number of cameras can stand up to the high ISOs like 6400-12800 that this type of work requires.
For Full moon exposures shot at near native ISOs, it’s still a good idea to push the histogram a bit further to the right. Just be careful not to make it so bright that you cannot bring it back down in post. The idea here is to increase image quality by making sure the shadows are as clean as possible without blowing any highlights. The key to this type of night photography is finding the right balance between ambient, and added light. I generally reduce the ambient exposure by 1-3 stops relative to my light painting. Remember that the height of the histogram is irrelevant. It’s how the tonalities extend across the horizontal axis that count. So if your shadows are well off of the left edge and are rather tall, and your highlights extend almost to the right edge of the histogram, but barely get off of the floor, you are doing it right.
With urban night photography, the best approach is to give an image as much exposure as possible without clipping important highlight detail, by using the blinking highlight indicator rather than the histogram. Newer cameras- especially ones like the D750 do a great job at controlling noise when you bring up the exposure in an underexposed image. This technique didn’t work with older cameras. The key to successful urban night photography is to determine just which highlights are important, and which ones can be sacrificed. Generally light sources in the frame should be allowed to clip, but not to blossom out past the edge of the light itself. Surfaces like walls or the ground under light sources should not be clipped, as it is important to retain detail in these areas most of the time.
It’s not necessary to have a big hump on the right side of the histogram, just a long flat tail that extends almost to the right edge is fine. The goal is to take advantage of the part of the sensor’s dynamic rage which has the greatest concentration of tonality- the highlights on the right side of the histogram! It’s helpful to do some testing with your particular camera to see what kind of exposure meets your requirements in each situation. If you plan to make exhibition prints, you’ll need to have more exposure than if you are simply posting images on line. The end use of the image is very relevant to image quality requirements.