Camera controls (I): focus

1994/04/01 Nogeras, Itziar - Elhuyar Fundazioa Iturria: Elhuyar aldizkaria

• Irudiak/Soinuak

As indicated in the previous number, the thumb can be removed between 2 m and infinity with fixed focus cameras. To focus the closest you need a variable focus camera, that is, objective of approach and distance from the film.

The closer the subject or subject of the target is, the more behind the film the image is formed. Therefore, the focus target should move away from the film.

The possibility of focusing has two main advantages: being able to take pictures of very close objects and make them feel focusing only on the same image.

To do this, the lens has a ring with a distance scale (sometimes a sign) (see figure above). It is also the widest ring. Moves relative to a fixed reference point, choosing the desired or necessary distance.

At one end of the scale is infinity (), i.e. the maximum distance. In this position, the lens is at the slightest distance from the film and focuses distant images (usually more than 15 m). At the other end there is a minimum distance. In this position, the lens is at the greatest distance from the film. This distance, depending on the quality of the target, varies from one target to another.

To choose the distance, in simple cameras, you must calculate the subject or the distance between the subject and the camera.

The cameras with higher quality direct view have a telemetry. With it, in the most luminous central part of the viewfinder the images are folded and, for it to be focused, that double figure must form a single.

In reflex cameras, thanks to its system of viewers, the same image as the lens in the film is shown before us. Therefore, just move the target ring to see the image gently. In these cameras the lens and distance between the focus screen and the lens is the same as between the film. Therefore, everything that is focused on the screen will also be in the film. In addition, there will be no parallax error (in No. 81 the parallax error is explained).

Sometimes in the center of the screen there are two small prisms. When the image is out of focus, the image is split in that area. On other occasions it is usually a mesh of small prisms, in which vikortitos appear when it is out of focus.

Image (a landscape, p. ex.) take their two photos. Better in the image at the front, near, if there is anything (person, plant, tree, e.g.) Take two photos: one focused from more than 9 m and another focused from less than 2 m, that is, the one at the front.