Panoramic cameras and methods

Short rotation (or SWING-LENS)

Short rotation is a term used to define cameras that have a lens that rotates around the camera's rear nodal point (the optical point from which the focal length is measured) opposite a curved film plane.^[1] As the photograph is taken, the lens pivots around its nodal point while, at the same time, a slit exposes the vertical strip of film that is aligned with the axis of the lens. The entire exposure usually takes only a fraction of a second and the camera's function is similar to that of viewing a scene by turning your head from side to side on a steady level. Also referred to as rotating lens or swing lens, this method often encompasses a very wide angle of view, similar to that of the fisheye lens, but without the extreme distortion of lines which is often seen in extreme wide-angle lenses. Typically, these cameras offer a field of view between 110° to 140° and an aspect ratio of 2:1 to 4:1. The images produced commonly take up 1.5 to 3 times as much space on the negative as the exposure made by traditional 35mm cameras. For instance, the traditional dimensions of an exposure on 35mm film is 36x24mm, while the dimensions produced from a short rotation camera with a 140° field of view would be approximately 58x24mm. Therefore rolls of 24-exposure film would only yield around 18 exposures. Notable cameras of this type include the Widelux, Noblex, and the Horizon. The more obscure Russian "Spaceview FT-2", originally an artillery spotting camera, took 12 shots on 39-exposure 35mm film.

The open back of the swing lens Horizon 202

camera, showing its curved film plane


Unfortunately, short rotation cameras have a number of limitations. They usually only offer a relatively small amount of shutter speeds and have poor focusing ability, with most models having a fixed focus, set to the hyperfocal distance of the maximum aperture of the lens. This is often as far away as 10 meters (30 ft) or more. To compensate for this, panoramic photographers desiring to shoot a subject in a closer range must use a small aperture to bring the foreground into focus, limiting the camera's use in low-light situations. For these reasons, cameras of this type are most often used outside, specifically for landscape or kite photography, where there is usually plenty of available light and there is less requirement for short focusing depths.







A negative from a 35 mm swing lens camera

Rotating lens cameras also produce a notable and odd "distortion" of lines. If the horizon, for instance, is placed even slightly off-center, the horizon line will bow slightly in the opposite direction. While this 'distortion' is in fact accurate and correct, it nevertheless looks unusual to the viewer. This is chiefly because the image, which was originally viewed and captured from a sweeping, curved perspective, is now viewed flat. To truly view the resulting image correctly, the viewer would have to produce a sufficiently large print and curve it identically to the curve of the film plane in the camera. Now, with the viewer panning their view, they can view the image most accurately. This type of 'distortion' can be reduced by using a swing-lens camera with a 'normal' focal length lens [the FT-2 has a 50mm while most other 35mm swing lens cameras use a wide-angle lens], and by photographing buildings from a corner location, not from the center of a flat surface.

Swing lens panoramic cameras have also been built --in small to very large sizes-- for use while suspended by kites [or helicopters, in the modern era].

Full rotation

Rotating panoramic cameras (also referred to as slit scan or scanning cameras) are cameras that are similar to the swing-lens (or short rotation) cameras, but are capable of 360° of rotation or more, because the whole camera rotates, not just the lens. A clockwork or motorized mechanism rotates the camera continuously and evenly and simultaneously pulls the film through the camera, in such a way that the speed of the film matches the speed with which the image moves across the image plane. Exposure is made through a narrow slit. Using only the central part of the image field produces a very sharp picture whose characteristics are very even from edge to edge. Historically, these cameras were, and still are, widely used for group pictures, particularly of athletic teams. Today, a digital rotating line camera also composes a full 360° panorama, line by line, where a linear sensor may have (for example) 10,000 sensor elements (e.g., produced in charge-coupled device technology), and a full 360° panorama may be composed in this case of about 120,000 individual `line images'. A resulting image is then (for this example) in the order of 1,200 Megapixel. Digital rotating line cameras are, for example, used for documenting historic buildings or sites. Notable digital cameras include the Panoscan and Eyescan.

Notable (non-digital) cameras include the Cirkut, Hulcherama, Leme, Roundshot and Globuscope, all of which are capable of 360° of rotation.

Fixed lens

Fixed lens cameras (also known as flatback and wide view or "wide field") are essentially panoramic cameras that have fixed, stationary lenses and a flat film plane - as opposed to the rotating lenses and curved film planes of short rotation panoramic cameras. These are the most common form of panoramic camera and range from relatively poor quality and inexpensive APS cameras, right up to the professional 6x17 and 6x24cm medium format variety. Larger panoramic cameras using sheet film have been made and are available in formats up to 10x24 inches. The key difference between an APS or 35mm camera's simply crop the normal frame into a panoramic aspect ratio, thereby losing a significant portion of the film area, while professional 35mm or medium format fixed lens panoramic cameras make use of the entire height of the film and have an extended film plane, giving higher resolution images. Another key benefit is that, due to the fact that these types of camera expose the film in a single instantaneously exposure like traditional cameras as opposed to the longer, sweeping exposure of other types of panoramic cameras, fixed lens cameras can make use of a flash. Flashes would not work consistently with rotational panoramic cameras because the flash, which usually are around 1/1000 of a second, would only be captured on the part of the image that is being exposed when the flash goes off, not the entire image. In addition to this benefit, these cameras do not cause linear objects to curve, making them the panoramic camera of choice for architectural photography.

With a flat film plane, 90° is about the widest field of view that can be captured with normal sharpness and without significant wide-angle distortion or light fall off by a traditional lens and camera using a single, flat piece of film. Lenses with up to 120 degrees angle of view are available, but require a center filter to correct for light fall off toward the edge of the image. Lenses that capture wider angles—up to 180° —exist, but are commonly known as fisheye lenses and exhibit extreme geometrical distortion but typically less brightness falloff at the edges than normal (rectilinear) lenses.

Notable cameras are the 35mm Hasselblad X-Pan and the medium format Linhof 612PC, Horseman SW612, Linhof Technorama 617, Tomiyama Art Panorama 617 and 624, and Fuji G617 and GX617.

More recently, a company named ImmerVision has created the new "panomorph" lens. This lens provides a full hemispheric field of view with no blind zone, typical of catadioptric cameras.

Segmented

Example of a segmented panorama. Taken with a Nikon Coolpix 5000 and stitched with PTgui.

Segmented panoramas, also referred to as stitched panoramas, are made by joining multiple conventional photographs with slightly overlapping fields of view so as to create a larger, panoramic image once assembled. In the days before digital photography, countless amateur and professional photographers attempted to create panoramic views in this way and found that the craftsmanship needed to match the images and hide the seams was all but unattainable. However, modern digital cameras and software are capable of stitching multiple images together with results depending largely on skill and the software used, and as of 2007 this is probably the most common technique for creating panoramic images. In order to correctly stitch images together without parallax error, the camera needs to be rotated about the center of its entrance pupil.^{[1] [2] [3]}

QuickTime VR and Hugin are two notable pieces of "photo-stitching" software, although a great many exist. The Cinerama motion picture process used three cameras, projectors, and strips of film to achieve a 146°×55° field of view with spectacular sharpness and detail (and noticeable seams).

Information From Wikipedia