Exposure control

The exposure metering gives the input for exposure control. Measuring the brightness of the subject plus/minus a possible exposure compensation provides the brightness of the subject and then it is time to select a matching combination of aperture, exposure time and ISO.

The question you have to clarify with your camera beforehand is: who takes care of what? It's your decision and you tell your camera in two parts:

• Who is responsible for aperture & exposure time – via the camera mode.
• Who is responsible for ISO sensitivity, in a separate ISO setting – with a button or menu, depending on the camera.

This type of operation has survived from the pre-digital area of photography until today. In analogue photography, the ISO sensitivity was fixed with the film inside the camera, only aperture and exposure time could be adjusted from shot to shot. The power of habit seems to play a big role; I have only come across two camera types that go a different way, more on that below.

P, S, A, M resp. P, Tv, Av, M with Canon are the camera modes for actively participating in exposure control. The modes with self-selected favourite settings are also belong to this group if you have assigned them P, S/Tv, A/Av or M.

Smartphones do not have these modes, but Samsung and Huawei, for example, have a "PRO" mode in which you can set exposure time and ISO. The aperture is unchangeable.

Here is the work allocation for these four modes:

The camera suggests a combination of aperture and exposure time. This is convenient, your camera will take care to avoid shutter speeds where there is a risk of camera shake and can also keep an eye on the focal length to decide.

Unlike in full automatic, however, you can change the selected combination. This is called programme shift. The pictures show an example of a corresponding camera display.

The common operation seems to be

• Tap the shutter release
• Then turn a wheel; on Nikon system cameras at the top right of the back with the thumb, on Canon and Sony system cameras with the index finger at the front next to the shutter release.
• The P indicator changes to P* and you can watch how the displayed aperture and exposure time change.
• To reset, you can turn the wheel in the opposite direction until the * disappears, switch the camera on and off, or if the exposure metering switches off after a few seconds, the programme shift may disappear again.

I have come across the following variants with compact cameras:

• There are none of the described dials, instead a dial further down on the back or a ring on the lens has to be turned.
• The programme shift is only possible if you activate the exposure lock beforehand (on a Canon experienced, press the Canon symbol exposure lock button for the exposure lock).
• The programme shift is only possible if no ISO automatic is active (seen with a Sony, more on ISO automatic below).

If this does not work for your camera, please refer to your manual.

The programme shift hits limits at the camera's largest and smallest aperture, so if it doesn't react, that may be the cause. And with flash photography, your camera will select a fixed exposure time of usually 1 ⁄ 60 s and then also ignore your attempt to shift the programme.

You set an exposure time, the camera chooses a suitable aperture.

The designation as S comes from shutter, Canon's Tv stands for "time value". Sometimes the mode is also called aperture priority, which is the same thing.

How to use it:

• Press the shutter release button if the exposure metering is not active.
• Then you can probably set the exposure time with a wheel on the camera. With Nikon system cameras, it's the rear one if they have two; otherwise, as with Canon and Sony, it's the front one.
• It may happen that it is not possible to set a suitable aperture for your desired exposure time. In this case, the camera will use the largest or smallest possible aperture and indicate this by flashing the aperture display. A photo would then be overexposed or underexposed.

You set an aperture, the camera chooses a suitable exposure time.

The designation A comes from the aperture, Canon's Av stands for "aperture value". 

Operation:

• Press the shutter release button if the exposure metering is not active.
• Then you probably have to set the aperture with a wheel on the camera. On Nikon, Canon and Sony system cameras it is at the front next to the shutter release.
• It may happen that no suitable exposure time is possible for your desired aperture, but this is rare. If it does, the camera will use the shortest or longest one and let you know by flashing the exposure time display. A photo would then be overexposed or underexposed.

You set an aperture and an exposure time.

Your camera may have an indicator to help you determine whether and how far the resulting exposure deviates from the automatically measured one. However, it does not intervene in the aperture and exposure time. You are responsible for the exposure yourself... at least most of the time. Because there are two situations in which manual control is also a kind of automatic:

• If the ISO automatic is switched on at your camera, it automatically adjusts the ISO sensitivity up and down to the aperture and exposure time you have chosen and you still have an automatic exposure through a back door.

If you are interested, please try it out on your camera, there may be differences depending on the manufacturer and model. It works for Nikon.

• If you shoot with flash, the camera will automatically adjust the flash brightness, unless you change the setting. If the flash is the main light source, you will have a kind of automatic exposure control.

To operate the manual mode:

• Tap the shutter release if the exposure metering is not active.
• Then you probably have to set the aperture with one wheel on the camera and the exposure time with another.

To set a fixed ISO sensitivity, you will probably find a button labelled ISO on your camera and then be able to set a value with a dial or arrow keys.

Otherwise you will need to go into the camera menus, again I have included sample photos and hope they are enough to help you find the right way on your camera.

ISO automatic means that the camera automatically changes the ISO sensitivity instantly when needed. ”When needed“ means if it is necessary to achieve desired apertures and exposure times.

The logic behind automatic ISO is:

• You can select an ISO sensitivity even when the automatic ISO is switched on.
• The ISO value you have set remains untouched as long as it matches the selected camera mode and your settings for aperture and exposure time, i.e. the camera can achieve a sufficiently large or small aperture and the exposure time will not be so long that camera shake is a risk.
• If the exposure time becomes too long or the largest possible aperture is no longer sufficient for a correct exposure, the camera increases the ISO sensitivity.
• In the camera menus, a maximum ISO sensitivity is preset, up to which the camera goes and only then does it allow the exposure time to increase further.

Slight deviations and additional subtleties are of course possible depending on the manufacturer and camera model.

The ISO automatic is wonderful for quick, spontaneous photography when you want to prevent camera shake caused by long exposure times. On the other hand, it can drive up your ISO sensitivity if you are shooting in the dark with a tripod and forget to turn it off.

With the enormous choice of camera models, there may be more that operate differently, but here are two I have come across so far:

Fv is a clever, contemporary variant of Canon, ”flexible automatic“:

• The camera suggests aperture, exposure time and ISO. 
• You can simply leave this as it is and shoot comfortably as in full automatic – or pick somebody out of the trio of aperture, exposure time, ISO and move it yourself at any time. The camera then only adjusts the others. This bundles nicely all options from other camera modes – one mode for everybody's taste and all occasions. Canon introduced it in 2018 with its mirrorless R models and I'm curious to see how it catches on over the years. Many, once they get used to it, don't want to miss it.

Fujifilm's system cameras have their own operating concept, which has a similarity to Canon's Fv mode:

• Two wheels on the top of the camera are for setting exposure time and ISO, a ring on the lens for aperture.
• Each of the three can be set to a fixed numerical value or to ”automatically“.

As a result the camera behaves as if it were in a P, S, A or M mode. It shows these symbols on a camera, but actually you don't need to know them at all, just look at the camera body to see which of the three settings is put to automatic.

This is Fujifilm's own very nice clear operating concept that sets it apart from other manufacturers.

This is mainly a question of your preferences in how to use your camera – you can achieve identical results with all camera modes.

Programmed auto P is convenient and fast. If you are taking snapshots and the exact exposure time and depth of field are not so important for your shooting situation, it is perfectly adequate. Together with ISO automatic, it is as flexible as full automatic, allows you to be quick, not to miss a shooting moment. That is my preferred choice for snapshots or at events where I photograph people. 

Aperture priority A/Av is my second choice, because the active selection of an aperture for the depth of field matters more often than the preselection of a certain exposure time. It is also often recommended in photography courses to use this mode to get into the habit of consciously setting an aperture.

Shutter priority S/Tv is for those situations where you really want to have a certain exposure time for a suitable amount of motion blur. This can be annoying with programme automatic and programme shift, because it can happen that with a slight camera swing the subject brightness changes and then the exposure time jumps up and down.

I rarely use the manual mode M. The reasons for it can be:

• Several pictures shall get exactly the same exposure, e.g. for a panorama where several pictures are later mounted together. But instead you can also work with another mode plus exposure lock.
  
• For flash photography, the manual mode is a way to achieve a long exposure time for the desired background exposure. But instead, you can also set the flash control to slow sync.
• Fireworks mess up any automatic system and are best photographed manually. ISO and aperture control the brightness of the fireworks and whether their colours can be seen, exposure time controls the length of the traces.
• You will notice from several clauses ”But instead you can also...“ that there are often several ways, i.e. several camera settings in combination leading to the same goal.