51 Weeks Photo Project: the Exposure (aperture, speed and ISO values)

Ooooh, welcome back!
The second macro-theme started yesterday: the Exposure (but not just this…).

After deciding how to frame your son making bubbles with the nose, either you chose to follo the Composition rules, or you feel particularly creative and chose to ignore them all, you’ll have to know how to set your camera to avoid this:

Overexposed photo

Or this:

Underexposed photo

(I can’t make bubbles with the nose, so I did the best I could).

If you shoot with a compact camera or with the phone, you won’t have to worry about this, because the settings are usually automatic.

This also applies if you bought a reflex, but shoot in AUTO mode (this makes no sense, for is like showing your friends your new kitchen worthy of a big chef and then cooking freeze-dried risotto for supper… yet you have the right to do that).

Although, if you shoot in Manual mode, you should know (or you’ll be happy to know) that Exposure is controlled by three things:

The aperture of the diaphragm

The diaphragm is the mechanism inside the camera lens controlling the amount of light hitting the camera sensor, through a variable size hole (the aperture).

Every objective has its own (minimum and maximum) aperture and this is usually indicated on the body of the lens with f/x (where x is a number).

The smaller the number, the wider the aperture. So, f/2 indicates a wider aperture than f/16. In a nutshell: the bigger the number, the smaller the hole (I know, written this way does not sound very technical, but I bet you’ll remember it :mrgreen: ).

Anyway, it’s only a supercazzola easy to get around: just think of it as a fraction et voilà 1/2 is bigger than 1/16. If you are as dumb as an ox in Maths you’d better try until it you’ll do ti automatically, it goes without saying 😀

The more light enters, the faster the shutter speed.

Here below a sketch (took from Phototutorial.net), much clearer than my explanation:

The number indicated in this sketch are the standard ones, but you can find lenses with a wider/narrower aperture.

Besides letting more light in, the diaphragm also controls the depth of field (often abbreviated DoF).

Just like they write in cool sites: this subject will be dealt with next month.

For now, then, be happy to know that:

– with a wider aperture you’ll have a shallower depth of field (just think of those photos in which there is element into focus while everything else is blurry), as in this photo:

shallow dog
shallow depth of field

– with a narrower aperture, you’ll have a deeper depth of field, that is more things into focus, as you can see in this photo:

deep dof
deeper depth of field

(Photos: Phototutorial.net)

Exposure time (or shutter speed)

With the diaphragm you control how much light to let in, while with the shutter you control for how long.

As regards Exposure, diaphragm and shutter are inversely related: with a wide aperture you will need less time to get a correctly exposed picture.

But the funny thing is playing with settings… 😉

This is a typical** timescale (from the fastest to the slowest):

[su_label type=”info”]**Some cameras have also intermediate time.[/su_label]

1/8000 of a second – 1/4000 – 1/2000 – 1/1000 – 1/500 – 1/250 – 1/125 – 1/60 – 1/30 – 1/15 – 1/8 – 1/4 – 1/2 – 1″ – 2″ – 4″ – 8″ – 16″ – 30″ – B (bulb)

The B-mode is to go beyond the 30 seconds: the shutter remains open while the release button is held down.

To say with my own words: the pair aperture/time makes me think of sun blinds: you can pull them completely down or lift them completely up, with several in-betweens, to have dark room. Depending on the light, your eyes will make more or less effort to see what’s in the room.

But since I am very bad at analogies, this relationship is often explained with the analogy of the glass of water, where the glass is the image to be shot, the tap is the diaphragm, the water is the light entering the camera.

A tap wide open will fill the glass in less time (this is a scientific truth, as well as a self-evident truth I could avoid to write down…).

water analogy
The glass of water analogy

(Image taken from Phototutorial.net)



The shutter speed is essential also to “freeze” the action, as in this photo:

1/200 sec. – f/14 (ISO100)

to render a sense of motion, as in this photo:

2,5 sec. – f/10 (ISO100)

or to simply avoid having a photo of your son making bubbles, in which he has three heads, because you shot him without using a tripod.

The correct shutter speed to set depends on what kind of photo we want to obtain, and also on the focal length of the lens.

A trick: to avoid blurry photos when holding the camera (and not using a tripod) use the reciprocal of the focal lenght rule: with a 50mm lens, the speed to set is not less than 1/50 sec, with a 300mm lens, the slowest speed you can set is 1/300.


Because there always comes a time when:

A. You’re shooting your son making bubbles, in the cellar, lit only by a candle. With the widest aperture and a shutter speed to avoid a blurry photo (as just explained here above), you get an underexposed photo. With the widest aperture and a shutter speed to avoid an underexposed photo, you get a picture in which of your son seems like being centrifuged.

But also

B. you’re shooting a person dressed in white and glitter under the midday sun in Greece, where all houses are white… ok, it’s just to get the idea. Let’s say you’re shooting your son making bubbles in the garden, on a sunny day. With the narrowest aperture and the fastest shutters speed, you get an overexposed photo.

What do you do?

Give up shooting that photo? You shoot a blurry photo? An underexposed or a burnt one?

You’re within your rights. But if, on the contrary, you just wished to shoot a simple picture, correctly exposed and not looking as shaken, you have the third option to play.

That is:

The ISO sensitivity

Once there was the film. If you are very young, you probably don’t know what I’m talking about and at best you’ll think about something with which you cover the freeze-dried risotto left from the supper with your friends. But I guess you figured out I’m talking about the analogically camera rolls, which had (and still have) different ISO sensitivity, depending on the intended use.

When you didn’t know how to chose one, on the pack there was a weather symbol or the drawing of a flash.

Here below, a sketch from Kodak (the Kodak Film Chooser), a sort of film cheat-sheet:

Kodak film chooser
Kodak Film Chooser

In our so-cool cameras (ok, also the less cool ones and even in the phone you got with the supermarket clubcard points, provided it has ha camera), the roll has been replaced by the sensor, but the underlying logic is the same.

According to the standard (ISO5800:1987 – just to be picky), the sensitivity of the film/sensor is divided into:

Low: ISO 25/50/100

Average: ISO 200/400/800

High: ISO 1600/3200/6400

Very high: ISO 12500/54000

The higher the sensitivity, the less light you will need to take the photo. You can find a clear explanation of how ISO sensitivity works and when to increase or decrease it HERE.


June 2018 - Update!

I just found a very interesting (and complete, indeed) post on ISO – and exposure –

HERE – Photography Talk

Very useful for beginners, but not only for them! I found some tips also for myself 😉

June 2018 - End of Update


So, getting back to the situations A e B here above:

  1. (in the cellar) raise the ISO value in order to set a faster shutter speed;
  2. (in Greece or in your garden) lower the ISO value to the minimum, in order to have less light into the camera and avoid “burning” the photo (in some cases even this will not be enough, and you’ll have to use external accessories).

Yet remember:

Low ISO= higher resolution = potentially a better photo

High ISO= lower resolution = more “grain”

To recap, Exposure is determined by the settings you choose for diaphragm (aperture), shutter speed, ISO values.

Further to the Exposure, these also control:

The Depth of Field:
  • open diaphragm (wide aperture)=shallow DoF;
  • closed diaphragm (narrow aperture)=deep DoF;
How movement is captured:
  • fast shutter speed = to “freeze” moving subjects;
  • slow shutter speed = to render a “fluid” movement.
The Definition (or Sharpness):
  • Low ISO = higher definition;
  • High ISO = more grain

Since this is a vast theme, I have split it onto 3 months, in 51 Weeks Project:

  • Shutter speed (from 5/02 to 26/02)
  • Depth of field (from 26/02 to 26/03)
  • Exposure (from 26/03 to 23/04)

See you soon!


The Project


51 weeks Photo project




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