Program mode

Most digital cameras support a number of digital camera modes for use in various situations. Professional DSLR cameras modes focus more on manual modes, consumer point-and-shoot cameras focus on automatic modes, and amateur prosumer cameras often have a wide variety of both manual and automatic modes.

Manual-enabled modes give the photographer control over the various parameters of an exposure. There are three exposure parameters – aperture, time (shutter speed), and sensitivity (ISO), and in different modes these are each set automatically or manually; this gives 2³ = 8 possible modes. For a given exposure, this is an underdetermined system, as there are three inputs but only one output. Accordingly, there are many combinations that result in the same exposure – for example, decreasing the aperture by one stop but increasing the exposure time or sensitivity to compensate, and there are various possible algorithms to automatically choose between these.

Most often, ISO is considered separately, being either set manually or set to Auto ISO, and then only aperture and shutter speed need be determined – either determines the other.

The four main modes, sometimes abbreviated "PASM", are:

Together with setting ISO manually or automatically, this (PASM) yields the 4×2 = 8 possible combinations of manual/auto.

Exposure is further controlled in each of the above modes with an independent setting for:

Less commonly seen modes include:

In cases where there is camera discretion (e.g., Auto ISO), different cameras allow different configuration of how decisions are made. For example, As of 2008^[update], Nikon cameras allow one to set the maximum and minimum ISO sensitivities, and slowest shutter speed that will be used in automatic modes, while Canon cameras will select within the fixed range of ISO 400–ISO 800 in Auto ISO mode. In Nikon cameras, the Auto ISO mode first adjusts the shutter speed, keeping ISO at its minimum desired value, then, when shutter speed reaches the user-defined limit, the ISO is increased, up to the maximum value.

All of the above functions are independent of lens focus and stabilizing methods.

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