The focus in a photograph has been challenged since the beginning photographer if you want to create a portrait of your wife. You fit the head in an iron collar fixed
to provide the necessary immobility, so that the world holds still for a while. You point the camera lens on his face, but unfortunately, you make a mistake with fractional inches, and when you take a snapshot does not represent your wife – it is his parrot, his watering pot – or worse.
Joke like that, this section highlights the practical difficulties experienced by early photographers. In doing so, it identifies three manifestations of the problem focus that is as real today as they were back. The most obvious problem is the burden of accurately focused on the subject prior to exposure. A poorly focused images evoke a sense of universal loss, because we all take granted that we can not change focus in a photograph after the fact. And focus accurately is not easy. Although the focus of modern automated systems to provide assistance, the error of “a fraction of an inch” in the film plane position may mean deliberately focus past your model to the wall in the background – or worse. This is a classic manifestation of the problem in focus.
The second manifestation is closely related. This is the fundamental coupling between
aperture size and depth of field – the range of depths that appear sharp in that picture. As a natural consequence of which the lens forms an image, depth of field decreases with increasing aperture size. This relationship defines a set of tension in the practice of photography.
how do i have to choose the correct aperture size? On the one hand, expanding the narrow aperture to reduce depth of field and blur the object away from the focal plane. In the figure on the background curvature becomes more pronounced as the aperture narrows. On the other hand, a narrow aperture requires a longer exposure, the natural increase of blur due to shake our hands while holding the camera and motion in the scene
1. In order to get a focus that is well-advised to take pictures of a moving object when the object is silent or are moving slowly.
2. use the auto focus setting on the camera used
3. lighting on the object sought is not excessive