Long exposures without turning night into day

Question

When taking Night Photography you will use long exposures. Sometimes these exposures can be very long. My question is this:

How can I take long exposures without turning a night scene into a scene that looks like its daylight? I have used ISO 100 and the smallest aperture possible. I have thought of using a neutral density filter similar to how you would in daylight to capture flowing water etc but I am not sure if this would work for night scene.

An example would be shooting star trials with a tree in the picture. The tree comes out looking like the photo was taken in daylight.

I have thought of using multiple exposures with multiple images and blending them in Photoshop but that is not always the easiest and if I can compose in camera all the better.

If it matters I am using a Nikon D5100.

Answer 1

There is no fundamental difference between light at night time and day time. The difference is where the light is coming from, and how bright it is.

If you are shooting with manual mode and at the lowest ISO and smallest aperture you are still getting an image that is too bright at your desired shutter speed, then you have to use a neutral density filter. A neutral density filter will allow you to select the aperture you want for the composition, rather than using aperture solely to reduce light.

For shooting star trails a stacked image technique may be more appropriate: http://www.jamesvernacotola.com/Resources/How-To-Photograph-Star-Trails/12233655_V7cX4D Stacking images will allow you to take a longer effective exposure without requiring any additional hardware. You will also avoid running out of battery half way through the exposure.

Answer 2

The real issue here is that your camera is trying to render the scene as if it were day light. That is what the meter is programmed to do - render what it is measuring as mid tones.

That is why photos with snow sometimes look under exposed - the camera is trying to render the snow as a mid tone. In your case if the meter is measuring the light reflecting off the tree it will try to render the tree's greens as mid tones. Exactly the same as during daylight. Our modern matrix meters do a better job of guessing what we are really trying to do but even then that metering mode is still metering for a daylight exposure.

If you want to control what the image looks like you need to override the automatic metering and tell it you want the tree to be darker than normal. The easiest way to do that is to use spot metering - which your camera has. If you meter off the tree and dial in say -1 exposure compensation you will get a dark tree that will not look like day time. In your case you might want to dial in -1.5 or -1.7 to make sure you have a night time look.

As an example I use this technique for my night time urban work (http://www.unfamiliarlight.com/2012/07/downtown-ottawa-at-night/). In my case I use the spot meter and manual exposure (usually with the bulb setting because most of my shots are over 30s long). For example I metered off the grey in the war memorial and to get a starting point for exposure. In these examples they are all made using HDR so I bracketed around that but the metering technique is the same.

Answer 3

It may not be obvious, but the moon reflects a significant amount of sunlight, even only a few days on either side of new.  As such, any long exposure night photography with a moon present in the sky will look like a daylight scene.

You didn't indicate how long your exposures are, but shorter is better - to reduce the impact of moonlight.

However, capturing star trails - as you use as an example - requires an exposure of significant length, so it's best to plan your shots based on the moon's phase, and where it is in the sky at your location when you plan to capture the image.

If you want to shoot late in the p.m., go for a period when the moon is late in it's phase, before new. If shooting in the early a.m. go for early phase after new.  If you want a really long exposure - all, or most of the night - plan for a shoot as close to new moon as possible.