Depth of field: definition

The depth of field (PDC) is the area of ​​space in which to find a topic that we can get an image that the human eye accepts as "net". It is bounded by the two extreme points where the image will be sharp.
Okay for the theory on the PDC, but in practice?

All this is nice, but what's the point? Again, it's very simple! When you take a photo, we do not always think, but there are two possibilities to us:
I take a landscape, or a close subject (animal, person ...) with a nice background: I rather like the subject and the background are clear both. For this, I will try to maximize the depth of field!
I take a close subject (portrait for example), and the background does not interest me, I want my subject looks sharp and stands a blurred background. I must then minimize the depth of field.
A picture is worth a thousand words ...

Here are two pictures taken with the same framing, playing only on the depth of field:











The first photo was taken in order to minimize the depth of field to emphasize the subject. The second image, however, was achieved by maximizing the depth of field.
How?

Ok, we now know the concept of depth of field, and its concrete manifestation in the image. Let us now proceed to obtain an image with shallow depth of field or on the contrary, a photo with great depth of field.
Aperture Priority

To play on the depth of field of a photo, we will use a setting that typically offer all cameras: the aperture.
To do this, we will use the Av mode (or A, depending on the aircraft), which will allow us to specify the opening of the diaphragm, while the camera will do the rest (for the curious, the "rest", c is the shutter speed!).
THE rule!

The rule, simple is as follows:
To maximize the depth of field, I chose a small aperture opening (it is often said "I shut up" ...).
To minimize the depth of field (have the background blur), I choose a wide aperture.
and ... THE trap!

Enough is enough. It was too easy! So there is a trap in there, you will require a little brain gymnastics, at least initially ...
Indeed, the aperture is expressed as a ratio, the "1 / x" style. However, the cameras do not show "1 / x", but "x". Mathematicians in the grass will include: to specify a large opening, I have to give a small x, and specify a small opening, I have to specify a large x. That's it!
Conclusion

To play on the depth of field, I select the Av mode (aperture priority), then I give a low value to minimize the depth of field, or a high value to maximize depth of field.
On your device, and keep this information in mind for your group photos (large depth of field so that everyone is net), photos of flowers (shallow depth of field so that the flower stands out from its background ) your portraits (ditto), your landscapes (great depth for all the plans are clear) ...
Questions about depth of field?

You have finished reading this mini-course on the depth of field, but you do not quite understand what it's all about or how to apply these tricks? You can come and talk and ask all the necessary questions on the forum of photographers, a thread devoted to it!