Low-light photography is specialized in that you are always pushing the technical limits. By definition,there is never quite enough light to allow the ideal camera settings, and you will always forfeit something. This area of shooting is all about thresholds and trade offs.
There are three main technical variables: Shutter Speed, Aperture, and ISO. You will need to decide which has priority.
Refers to a setting on some cameras that allows the user to choose a specific shutter speed while the camera adjusts the aperture to ensure correct exposure. This is different from manual mode, where the user must decide both values, aperture priority where the user picks an aperture with the camera selecting the shutter speed to match, or program mode where the camera selects both.
Shutter priority with longer exposures is chosen to create an impression of motion. For example, a waterfall will appear blurred and fuzzy. If the camera is panned with a moving subject, the background will appear blurred. When photographing sports or high-speed phenomena, shutter priority with short exposures can ensure that the motion is effectively frozen in the resulting image. Shutter priority is often abbreviated with Tv (literally, “time value”) or S on a camera mode dial. (source – Wikipedia)
Often abbreviated Av (for Aperture value) or A on a camera mode dial, is a setting on some cameras that allows the user to choose a specific aperture value while the camera selects a shutter speed to match. The camera will ensure proper exposure. This is different from manual mode, where the user must decide both values, shutter priority where the user picks a shutter speed with the camera selecting the aperture to match, or program mode where the camera selects both.
The main purpose of using aperture-priority mode is to control the depth of field. Aperture priority is useful in landscape photography, where a narrow aperture is necessary if objects in foreground, middle distance, and background are all to be rendered crisply, while shutter speed is often immaterial. It also finds use in portrait photography, where a wide aperture is desired to throw the background out of focus and make it less distracting.
Another common use of aperture priority mode is to suggest how the camera should determine a shutter speed, without risking a poor exposure. In landscape photography a user would select a small aperture when photographing a waterfall, hoping to allow the water to blur through the frame. When shooting a portrait in dim lighting, the photographer might choose to open the lens to its maximum aperture in hopes of getting enough light for a good exposure.
In addition, aperture priority mode allows the photographer to force the camera to operate the lens at its optimum apertures within its aperture range for a given focal length of the lens. Commonly, lenses provide greatest resolving power with a relatively medium-sized aperture. (source – Wikipedia)
Often abbreviated Sv (for Sensitivity value) on a camera dial, is a setting on Pentax cameras that allows the user to choose a specific Sensitivity (ISO speed) value while the camera selects a shutter speed and aperture to match. The camera will ensure proper exposure. This is different from manual mode, where the user must decide all three values, shutter priority where the user picks a shutter speed with the camera selecting the aperture to match, or program mode where the camera selects all three. (source – Wikipedia)
The key to technical success in low-light photography is to know what the acceptable thresholds for each of these is for you. This means familiarizing yourself with, at the very least, the noise characteristics of your camera, your ability to hold the camera steady when hand-held, and the shutter speed needed for any kind of movement in the frame. Then you have to prioritize, and that depends on the situation and on what you personally are prepared to accept as minimum image quality. Some motion blur might well be acceptable, depending on where it happens in the frame and how it looks, or you might prefer more noise in order to avoid this. Only you can make these decisions.
Shooting hand-held under low ambient lighting conditions required a relatively fast shutter speed to avoid as much as camera shake as possible. This meant using a fast ISO and accepting that there would be noise in the image.
Because noise is a relatively new thing from digital slr photography, it gets a lot of attention, which is fine, but when set against camera shake, subject motion blur, and the difficulties of achieving sharp focus with wide apertures, it is not the only image quality issue to deal with. A noise image from a high ISO setting is at least a workable, recognizable image, while the alternatives-blur or underexposure-are useless.