Exposure Triangle At Night
You may have heard of the exposure triangle (ISO, shutter speed, aperture), but how does it work when capturing images at night? Along with trying to get tack-sharp images, getting the right exposure while shooting at night is one of the biggest challenges to overcome.
When shooting at night, the elements within the exposure triangle will be pushed to the limit. The high ISO needed to capture an adequate amount of light will introduce plenty of grain/noise, the shallow aperture will limit the depth of field (luckily, the stars won’t be too affected by this in your image due to their distance and size; ultra-wide lenses with an f/2.8 aperture can appear sharp at night from infinite to 3-5 yards away while medium lenses with an f/1.4 aperture can appear sharp at night from infinite to 5-10 yards away), and slow shutter speed could cause motion blur (even when the camera is placed on a tripod) due to the earth’s rotation.
The downside of using a high ISO is the inability to cleanly make adjustments to the shadows during post. Dynamic range is limited, and this is one area where image quality can suffer. The downside for using a very slow shutter speed includes the introduction of thermal noise (which appears as tiny dots) and motion blur caused by the earth’s rotation (as mentioned before). While the star trails caused by the blur can be used for creative effect, they’re not always wanted.