Had a teacher in photo school make the comment that if you put a camera in a dark room, release the shutter and then come back in a little bit there will be no picture. that it requires light to make a photograph. The comment was preface to an exposure discussion but on the face of it tends to make sense. Photography is all about light, right?
Except with sensitive media like fast film or today’s digital sensors. The camera can see light that we miss. Light is all around us, in general, especially in suburbia where there is generally too much light. Anyway, cameras can seem to do magic by revealing a world in the dark that we just don’t see. Don’t believe me? Set your camera on a tripod on a dark night, point it at the horizon and leave the shutter open for a minute at about f/8. You’ll be surprised at what you get.
It’s not really magic, though. Whereas our eyes collect light continuously they also “refresh” continuously. After sending the information in a scene to the brain those little rods and cones in our retina (some of that high school biology coming back?) literally bleach out that scene and start collecting light for the next scene. Because the process is always going on our eyes never really collect enough information to make a nighttime scene very bright.
Compare that to a digital sensor (or high ISO film). As long as light is hitting it, even just a few photons at a time, it continues to build up image information as long as the shutter is open. Only when the shutter closes is that information passed to the chip in the camera for processing into an image. So, leave the shutter open long enough and those pixels will gather enough light to form an image. Even on a pretty dark night.
Naturally an image of a dark sky and dark ground probably won’t be very interesting (unless you’re fond of star trails or streaking car lights) so when photographing at night it’s better to find something interesting. Here’s where the light pollution comes in handy, as well as a few clouds in the sky.
The clouds are reflecting the myriad of streetlights around the neighborhood and silhouetting the grove of trees nicely. The broken up nature of the clouds also makes the sky more interesting than solid white or black. Drive around long enough and you’ll find something on the horizon that looks more interesting at night than in the daytime.
Since HDR is all about extracting more information from the image, I tried the single-image-HDR process using the new NIK HDR Efex Pro plug-in for Photoshop. I wasn’t really trying to get a “natural” look in the image – just wanted to see what moving some sliders around would give me.
I was able to pull more detail out of the foreground shadow, at least so you can see there aren’t any buildings hiding there. One problem with shadows in long exposure images is the low signal-to-noise ratio – you end up with lots of noise with little signal. No amount of de-noising or sharpening will bring more detail out. You have to expose longer so the sensor will build up more of the image. Of course that would blow out the exposure on the clouds so now you’re back to more traditional multi-image HDR. I’ll try that in the future to see what I can get.