Monday, 01 January 2018 14:46

The focus

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The focus of the subject in a photo shoot is one of the basic points that allows the photographer to take good pictures and customize the composition of the shot as desired. In general, a photograph is considered technically successful when it is clear, that is when it is perfectly in focus. The modern cameras are equipped with autofocus very valid and fast, but the focus management software is not always able to focus correctly on the subject or the whole picture so it is essential to understand the operation of the automatic system of focusing of our SLR so you can intervene manually if necessary. First of all, let's see how the focus works on a DSLR.
Focusing means intervening on the lens / sensor distance, to ensure that the lens projects a clear image of the subject to be photographed on the sensor, in particular checking that:
When the subject is far from the point of recovery, the lens causes the distance to decrease between lens and sensor;
When the subject is close to the shooting point, the lens moves away from the sensor.
This operation is similar to when we use a magnifying glass and approach it and move away to focus on the text we want to read.
As mentioned above, we often think that it is sufficient to rely on the automatisms of autofocus to make the subject of our composition clear. The precision of the modern and advanced autofocus systems of the more recent SLRs are not in question, but two important aspects must be kept in mind:
Spectal photographer deciding which part of the subject should be focused at best
It is not always easy for the automatic device to be able to distinguish the best point of focus
However, it is not always easy for the automatic device to distinguish the best focusing point, even if on the SLRs it is possible to choose the points and the zones to be used to calculate the distances, the device may find it difficult to set correctly of fire. Or, more simply, the setting of the automatism does not coincide with the will of the photographer. To overcome these problems, it is possible to switch to manual mode that in most of the SLR is done by moving the switch from AF to M directly on the lens and using the barrel rotation device to move the lens away from the sensor and find the correct point of fire.

What does it mean to focus on a composition? It does not necessarily mean that all the photography should be in focus perfectly, but it is possible that the needs of the composition can ensure that only the main subject is perfectly clear. Let's see some situations and how to behave in this case.

Main subject consists of distant objects
It is perhaps the least complex situation. The subject must be pointed at a considerable distance and the diaphragm can be quite open

Subject includes things close and distant things:
If our subject is made up of things near and far, it is necessary to decide how the camera is to be set to achieve the desired focus. Let's see the cases in which:
All the composition must be in focus (landscape photos)
          To obtain the solution to this situation, the hyperfocal distance must be calculated. The hyperfocal distance is the distance beyond which all objects have an acceptable sharpness, setting the focus to infinity. Once the hyperfocal has been calculated, it is sufficient to focus at that distance to have the whole frame at an acceptable sharpness. But how is this distance calculated? There is a mathematical formula for calculating this distance

  • The background must be blurred
              The subject is to be focused and the lens diaphragm opens. The more the diaphragm is open the more the background is out of focus and the subject is isolated. Keep in mind that the lower the focal length, the greater the depth of field, the less you can blur the background.

    Main subject consists of things a little more than a meter
    Here the situation turns out to be more critical because the closer we get to the smaller subject is the depth of field and the photo could be blurred both behind and in front of the main subject. If the blur behind the subject can be useful to isolate the subject and is accepted by the human eye, a blur in front of the subject is not tolerated. To avoid this problem it may be sufficient to focus at a shorter distance than the main subject paying close attention to the depth of field that can be very limited

Read 1422 times Last modified on Monday, 01 January 2018 15:58

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