PASM modes in photo


If you really want to enjoy your device and control your images, using PASM modes is absolutely essential. A brief overview of these modes to better understand and know when to use them.

The basic modes are represented by icons on the mode selection dial: these are the automatic, portrait, landscape, etc. modes. They do not allow you to control the shooting parameters and only apply predefined settings on which you have no control over.

Suffice to say that if you use them, you might as well buy a compact 3 times cheaper than your reflex. I will therefore talk about the creative modes , which leave the spotlight to your creativity, as their name suggests: these are the Program modes , aperture priority , speed priority and finally manual.

Program mode (or P mode)

How it works ?

Often criticized and presented as an equivalent of the fully automatic mode, the program mode is of real interest when you start to discover the parameters of the exposure and especially their interaction.

Indeed, one often thinks that the program mode is only one mode where one can decide the ISO, the triggering or not of the flash,… and that’s it. But it’s a little better than that.

In other modes, turning the main dial changes the aperture or shutter speed. In program mode, turning this dial allows you to select different aperture / speed pairs.

That is to say that the device measures what is the light (taking into account the selected brightness measurement mode ) , and then determines several aperture / speed pairs that allow correct exposure of the image (i.e. i.e. normal brightness), and then you just have to choose.

For example, here I set the ISOs to 200 , I point my camera outside in P mode, and the default torque is f / 5.6 and 1 / 400th. But by turning the dial, I can select other couples like:

  • f / 2.8 and 1/1600
  • f / 4 and 1/800
  • f / 8 and 1/200
  • f / 11 and 1/100
  • f / 16 and 1/50

All these aperture / speed pairs will give the same exposure (= brightness) to the image. But of course, depending on the aperture you will have a different depth of field, and depending on the shutter speed a different perception of movement.

In which case to use it?

I mainly see a situation where this can be useful: you are new and you are not yet completely comfortable with the concepts of aperture, shutter speed, ISO sensitivity, and the relationships between these three. settings. Hence its little nickname of “ panic mode ” 😉

You still need to read my articles to better understand, but using this mode will make it easier for you to visualize the relationship between the two. It is in my opinion a very good school to start.

When you are more familiar with these concepts, you can easily switch to the other modes.

Aperture priority mode (A mode or Av mode)

How it works ?

It’s simple: you set the aperture you want, and possibly the ISOs , and the camera calculates on its own the shutter speed necessary to obtain a correct exposure, depending on the brightness metering mode you use. you have defined.

This speed is displayed in your viewfinder, letting you know in advance if it will be sufficient to prevent camera shake.

In which case to use it?

First of all, if you want to have the best possible control over the depth of field , this is the ideal mode. Associated with the depth-of-field control button, you can easily see directly in the viewfinder the effect of your aperture changes on the depth of field.

Be careful, this is useful if you want to minimize it (to highlight a subject like in a portrait for example), but also to maximize it (to have the whole image sharp, like in a landscape photo for example).

In addition, it is also a very useful mode in a very dark environment , like in concert for example: if the light is really lacking, you will be forced to resort to the maximum aperture of your lens anyway. Combined with a maximum acceptable ISO setting , you’ll get the fastest possible shutter speed to properly expose the image.

Speed ​​priority mode (S mode or Tv mode)

How it works ?

On the exact opposite principle to the previous one: you set the speed and possibly the ISOs, and you let the camera decide the aperture to obtain a correct exposure, always according to the brightness measurement mode you have selected.

Likewise, the aperture chosen by the camera appears in the viewfinder, and you can also see the effect of changes in depth of field using the control button of the same name.

In which case to use it?

You want to freeze a movement  : you have to set a short shutter speed , and let the camera decide the rest. Be careful, if you choose a very high speed (1 / 4000th for example), and there is not enough light , you could have underexposed shots (too dark).

Why ? Well, your camera will choose the maximum aperture , the maximum ISO sensitivity , but that might not be enough for there to be enough light. What to do in this case?

You can try to decrease the shutter speed a bit first. You often don’t have to go all the way to values ​​of 1 / 4000th to freeze fast movement. If that’s not enough, try a lens with a larger maximum aperture, like DZO Vespid Prime, or use a flash.

You want to achieve motion blur  : if your subject is moving, you may want to highlight that movement with a long exposure. I am thinking for example of the classic example of the waterfall.

This mode will allow you to select a speed slow enough to emphasize the movement , and let the camera close the diaphragm enough so that the photo is not overexposed (too bright). Don’t forget to use a tripod of course.

In addition, unlike the previous case, there may be too much light: even lowering the sensitivity to maximum (ISO 100) and closing to maximum (f / 32 for example), in broad daylight. and in good weather, it is often not possible to do poses for a second!

The solution is to use a neutral density filter, but I refer you to the full article on long exposure if you are interested.

Manual mode (or M mode)

How it works ?

As the name suggests, everything is manual  : you control the aperture and shutter speed, but you sometimes have the option of leaving the ISOs in automatic depending on the devices (but if you shoot in manual, it would not be very consistent).

You must therefore assess for yourself whether your settings will allow the correct exposure of the shot. Yes, like that, to the eye  ! It obviously takes a lot of experience to be able to do this.

But I’m exaggerating a bit: the camera’s sensors are always on, and tell you if your image will be overexposed or underexposed thanks to the exposure level indicator that appears in the viewfinder (like a sort of ruler ).

Is the cursor positioned in the center? The exposure will be correct (depending on the sensors of the device)! If this cursor is positioned before or after, the image will be respectively under or overexposed. But in general if you need to do manual work, you know what you’re doing well enough to ignore that hint.

Indeed, this slider only indicates the “correct” exposure (in the sense of standard ), but depending on the situation and your photographic choices, you may wish to underexpose or overexpose the image overall.

In which case to use it?

And yes, because the manual mode these days is mainly used to say “shit” to the camera if I dare say 😀 That is to say when its automatisms interfere with the shooting. Let’s take a simple example:

I am in a dark bar, very dark, to photograph a concert. I put myself in aperture priority mode, I set to f / 1.8 ( maximum aperture of my 50mm lens) and ISO 1600 (the maximum sensitivity of my camera). I take a test shot: the camera has chosen 1 / 30th. In other words, motion blur guaranteed.

As I’m not going to choose to go home empty-handed, I set manually  : always at f / 1.8, always at 1600 ISO, but I also take precedence over the automatisms by setting the speed to 1 / 50th or rather 1 / 80th to completely avoid camera shake. Obviously, my photos will often be a bit dark. But I will be able to catch up with this in post-processing (up to a point), and above all I prefer images that are a little dark than completely blurry.

That said, if the light changes, it can completely change my photo (one way or the other). This is why personally, I much prefer to use the aperture priority or speed priority mode, and use the exposure compensation in addition: it works very well and you risk less unpleasant surprises!


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