Материал из ФотоЭнциклопедия.рф
| view camera operator using|
black cloth as sun shield
image by Elmo Alves (Image rights)
A large format camera is one that typically takes film that is at least 4x5 inches (or 9x12 cm) or larger. Such cameras use emulsion coated glass plates or sheet film, rather than the roll film most casual camera users are familiar with. Each exposure requires separate piece of film to be inserted in the camera.
Because of this, and because taking pictures with a large-format camera is generally more complex and time-consuming (and expensive!) than with smaller roll-film cameras, they're usually used for carefully-selected subjects, such as landscapes, architecture, or portraiture. Because the film is so much larger, the image quality is correspondingly higher. With larger cameras, such as 8x10 inches, prints can be made from negatives simply by contact printing.
In a large-format camera, the scene is composed and focused using a ground glass. This is simply a piece of glass which is ground (rough-textured) on one side (the side facing the lens, generally). When the ground glass is placed in the film plane in the back of the camera and the lens opened wide, the scene is projected on the glass, upside down and backwards. The photographer can then use this projected image to frame the scene and focus it, sometimes with the aid of magnifiers. A dark cloth placed over the back of the camera, under which the photographer ducks, shields the glass from light and makes it brighter and easier to see.
|image by Ben+Maggie (Image rights)|
Some, but not all, large-format cameras have controls which allow the geometric relationship of the film, lens and subject to be changed from their normal arrangement. (The "normal" setup is where the film and lens planes are parallel, with the film centered on the axis of the lens.) Such controls, known as tilts, shifts and swings (or just "movements" in general), allow the lens and film to be shifted and tilted with respect to each other, and with respect to the subject. These kinds of controls (sometimes erroneously called "perspective control", since they don't actually change the perspective—that can only be done by moving the entire camera with respect to the subject), enable the photographer, for example, to take a picture of a tall building looking upward and to correct the converging lines which naturally occur. Camera movements can also be used to control which parts of a scene are in focus, and to increase the depth of field of a picture. For example, when photographing a subject in the foreground against a landscape, if the lensboard is tilted forward, this will allow the subject at the bottom of the frame and the background above it to be in relatively better focus.
- read that all in depth with a little more mathematics ...
- ... or a bit more brief and animated ;-)
- view cameras going digital
| Ansco Universal View Camera (5×7 inch format)|
image by Irina Mashurova (Image rights)