The letters on the mode dial
P, A, S and M are not difficulty levels. Each hands you a different control and does the arithmetic on the rest.
The mode dial is not a difficulty ladder with automatic at one end and expertise at the other. Each mode hands you one control and works out the others.
What each one does
| Mode | You set | Camera sets |
|---|---|---|
| P — Program | Nothing; you can shift the pairing | Aperture and shutter |
| A or Av — Aperture priority | aperture | Shutter |
| S or Tv — Shutter priority | shutter speed | Aperture |
| M — Manual | Both | Nothing |
iso sits outside this and can be automatic or fixed in any of them.
Canon writes Av and Tv where most others write A and S. Same modes, different labels.
Choosing between them
The useful question is: which control does this photograph depend on?
Aperture priority when depth of field is what matters — portraits, landscapes, anything where the background is part of the decision. This is what most working photographers leave their cameras in.
Shutter priority when movement is what matters — sport, children, running water. You are saying “whatever else happens, do not go slower than this”.
Manual when the light is constant and you want it to stop changing between frames, or when the scene keeps fooling the meter and you are tired of arguing with it via exposure compensation.
Program when you want the camera to get you something usable while you think about where to stand.
Auto ISO changes the picture
Turning ISO to automatic changes what these modes mean. In aperture priority with auto ISO, the camera has two controls to play with, so it will hold a sensible shutter speed and raise the ISO rather than letting the shutter drag.
Most cameras let you set a minimum shutter speed for this, which is worth finding. It turns aperture priority into something close to “choose the depth of field and never let me get camera shake”, which is a genuinely useful thing to have.
The scene modes
The pictograms — running figure, flower, mountain — are aperture or shutter priority with the decision made for you. The running figure is shutter priority. The flower is a wide aperture.
Nothing wrong with them, but they hide which control they are moving, which makes them poor for learning. You already know what they know.
Key takeaways
- Each mode gives you one control and calculates the rest.
- Aperture priority when depth of field matters; shutter priority when movement does.
- Manual is for constant light or a meter that keeps guessing wrong, not for showing off.
- Auto ISO turns aperture priority into a much more capable mode.
Common questions
Is manual mode better than the others?
No. Manual is useful when the light is constant or the camera keeps guessing wrong. Aperture priority is what most working photographers use most of the time, because it is faster and the camera is usually right.
What is the difference between A and Av, or S and Tv?
Nothing. Canon writes Av and Tv where Nikon, Sony and others write A and S. They are the same two modes with different labels.
Next steps
The exposure triangle
Three controls decide how bright a photograph is, and each one changes something else as well. That trade-off is the whole of exposure.
Metering, and why it lies
Your camera's meter assumes every scene averages to mid-grey. Knowing when that assumption fails explains most automatic exposure mistakes.
Aperture and depth of field
The aperture controls light and how much of the scene is sharp at the same time. It is the control that most changes how a photograph feels.