I’m going a little out of order with the posts, but Danny Green’s post is going to be a lot longer than this one, so I wanted to get this one done first, since it’s going to be a bit more technical too.
Last night I met up with Douglas Lee Coon Jr., Sr., and Scott Papek to shoot some night photos. Having three other people around at night helped give me the motivation to shoot in the middle of the night. We met at Bird Rock a little after 11pm..
The tide was quite high, almost splashing up on the rocks at the stairs, so we had to shoot from the balcony. This prevented me from being able to get any rocks in the foreground, so bird rock is basically just a floating island in the ocean in these photos. It would have been possible with the 11-16mm- anyone like this shot enough to buy a print so that I can save up to buy a new lens?
Processing was mostly converting to a tungsten white balance to bring out the colors in the sky and selectively desaturating certain color channels to get a good look. In that shot, I was able to bring out the rocks lurking just beneath the surface of the water.
I think next time, I’ll use my telephoto for some detail work. The blurred interface is really the most interesting part of the shot for me, and I’d like to call some more attention to it.
For those that care about a photo-geek explanation of exposure, noise reduction, and ISO, keep reading. For those that don’t, scroll down the the next photo.
The other guys were using a different technique than I was. While I stuck with a lower ISO, longer times, and darker shots, they used higher ISOs for shorter exposure times and brighter shots . The downside to this approach is that it required the use of a dark frame to reduce noise. A digital sensor builds up a lot of noise during either a high ISO shot, a very long exposure of greater than several seconds, or especially if both are used in combination. This is the digital equivalent of film grain, and the price you pay for the luxury of increased sensitivity to dim light. Noise is built up by the heat given off by the sensor itself, and is registered as a signal by the sensor. With such low amount of light (signal) making it to the camera during a night shot, the noise becomes a large percentage of the total signal the sensor reads, and has a lot more time to accumulate during a multiple minute exposure.
This signal is non-image forming information in the shot. Our eyes can tell the difference between signal and noise, but it’s much more difficult for a computer to determine if a certain pixel is 20% brighter than its neighbor because it’s supposed to be, or because that pixel captured some sensor noise during the exposure and it registered as additional light.
That’s where a dark frame comes in.
Let’s say I took a shot that lasted 5 minutes at ISO 1600 in order to get enough exposure to register as a properly exposed image. That shot is going to have a lot of noise in it. Now if I put the lenscap back on the lens and take another shot at the same exposure time and ISO, I’m going to get (hopefully) the same amount and pattern of noise in that shot, but no image. So, the camera knows that any pixels that have any signal at all are picking up noise, and just how noisy each pixel is. It then takes that information and subtracts it from the previous image, thus subtracting the noise. It’s not a perfect process, but it’s as good as can be done without using some noise-reduction software to clean it up. If a camera has an option for long exposure noise reduction, or high ISO noise reduction, this is what the camera does automatically- basically reading the sensor noise without opening the shutter for the amount of time that the shot was for.
By the way, in film, noise is greater in higher ISO films because the silver halide particles are much larger than in a lower ISO film, among other things. Film exposure is not a linear phenomenon at extremely short or long exposures, but high-intensity and low-intensity reciprocity law failure will have to wait for some other post, which will probably never get written. HIRF and LIRF don’t occur with a digital sensor since it’s constanly reading the signal amount, which is a huge benefit to doing night photography with digital.
The problem is that the 5 minute dark frame makes it impossible to take another shot until it’s all done, so a 5 minute exposure now takes 10 minutes before I can make any focus/ composition adjustments and try again, and that one will take another 10 minutes, and so on. If it’s dark outside, autofocus doesn’t work, and the view in the viewfinder is pitch black so it might take a few tries to see if I’m focused properly, have a straight horizon, and the edges of the frame aren’t cutting off an important feature in the image. This makes night photography an extremely slow process.
Which is why I don’t do it.
By using a wide aperture and a high ISO, I was getting exposures of about 30 seconds which were bright enough to check for focus and composition thanks to the streetlights. Then I brought the ISO down to 200 (the native resolution of the sensor), stopped down, and increased the exposure time. Most of my exposures were around f/8 and 8 minutes. By using a lower ISO, the sensor isn’t as sensitive to noise, and I didn’t have to bother with a dark frame. I’d rather have the shutter open twice as long and blur more waves. Sure, I can’t just pick up my camera and move to another location during the dark frame process, but I had plenty of time to plan my next shot anyway, so that wouldn’t really save me much time anyway.
OK, back to something interesting.
With limited shooting options at Bird Rock, we headed over to the north end of Windansea Beach, and I found some shoreline I’ve never shot before.
The waves were actually coming up within feet of my tripod, it’s almost a shame that the energy and liveliness of the ocean doesn’t come through in these shots since the waves get blurred out.
Light pollution becomes the prominent light source for most city-based night photos. The moon was bright, but covered by clouds, so it barely registered as an exposure, except in the shadows that the streetlamps didn’t reach.
For an example of a test shot at ISO 1600 shot done for 20 seconds, take a look at the amount of noise present- it’s actually not much after a quick tap of the noise reduction slider in Lightroom.
There’s no longer exposure of that setup since during the next test shot, a big wave crashed against the rock I was standing on and I was about 12 inches away from drenching myself and my camera. I figured that was enough excitement for one night. So now, that’s a self portrait.