Ground glass is glass whose surface has been ground to produce a flat but rough (matte) finish, in which the glass is in small sharp fragments.
Ground glass surfaces have many applications, ranging from ornamentation on windows and table glassware to scientific uses in optics and laboratory glassware.
In photography, a sheet of ground glass is used for the manual focusing in some still and movie cameras; the ground-glass viewer is inserted in the back of the camera, and the lens opened to its widest aperture. This projects the scene on the ground glass upside down. The photographer focuses and composes using this projected image, sometimes with the aid of a magnifying glass (or loupe). In order to see the image better, a dark cloth is used to block out light, whence came the image of the old-time photographer with his head stuck under a large black cloth.
A ground glass is also used in the reflex finder of an SLR or TLR camera.
In motion-picture cameras, the ground glass is a small, usually removable piece of transparent glass that sits between the rotary disc shutter and the viewfinder. The ground glass usually contains precise markings to show the camera operator the boundaries of the frame or the center reticle, or any other important information. Because the ground glass is positioned between the mirror shutter and the viewfinder, it does not interfere with the image reaching the film and is therefore not recorded over the final image, but rather serves as a reference for the camera operator.
Ground glasses commonly serve as a framing reference for a desired aspect ratio. Because most films shot with spherical lenses are shot full-frame and later masked during projection to a more widescreen aspect ratio, it is important not only for the operator to be able to see the boundaries of that aspect ratio, but also for the ground glass to be properly aligned in the camera so that the markings are an exact representation of the boundaries of the image recorded on film.
Ground or frosted glass is widely used as a weather- and heat-proof light diffuser in ambient lighting, namely on glass covers or enclosures for lamp fixtures, and sometimes on incandescent bulbs. Its functions include reducing glare and preventing retinal damage by direct sight of the lamp filament. This hides unsightly details of the lamp and fixture without blocking its light, yielding a softer illumination without giving hard shadows.
Ground glass surfaces are often found on the glass equipment of chemical laboratories.
Glass flasks, stoppers, valves, funnels, and tubing are often connected together by ground glass joints, matching pairs of conical or spherical surfaces that have been ground to a precise shape.
Flasks and test tubes often have a small ground-glass label area on the side. (Pencil writing on ground glass is largely inert, rub-proof and waterproof, but can be easily erased.)
An optical microscope may include a ground- or frosted-glass diffuser to evenly illuminate the field behind the specimen. Microscope slides are often ground on the sides and beveled on the corners to soften the edges for safer handling.
Popular belief for many centuries is that ground-up glass (i.e., glass broken into tiny fragments) can kill if swallowed. In fact, this is a myth, as it is largely ineffective. [1] [2]
The Guy de Maupassant short story "La Confession" concerns a jealous girl who poisons her older sister's suitor by inserting ground-up glass into cake. [3]
The term ground-glass, as it relates to poisoning, is a corruption of grain d'église, the term given by the French in India to the seeds of the Jaquirity or Rosary Pea plant ( Abrus precatorius ). The seeds contain the extremely toxic lectin abrin, whose toxicity is over 30 times that of ricin. [4] These seeds have been used in India to kill cattle, and in homicides. Captain F. C. Briggs, adjutant to General Reginald Dyer, died of 'powdered glass' poisoning before he could give evidence to the Hunter Commission examining the Jallianwalla Bagh massacre. [5]
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses.
A single-lens reflex camera (SLR) is a camera that typically uses a mirror and prism system that permits the photographer to view through the lens and see exactly what will be captured. With twin lens reflex and rangefinder cameras, the viewed image could be significantly different from the final image. When the shutter button is pressed on most SLRs, the mirror flips out of the light path, allowing light to pass through to the light receptor and the image to be captured.
Laboratory glassware refers to a variety of equipment used in scientific work, and traditionally made of glass. Glass can be blown, bent, cut, molded, and formed into many sizes and shapes, and is therefore common in chemistry, biology, and analytical laboratories. Many laboratories have training programs to demonstrate how glassware is used and to alert first–time users to the safety hazards involved with using glassware.
A camera is an optical instrument used to capture and store images and videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photography and videography, cameras have played a significant role in the progression of visual arts, media, entertainment, surveillance, and scientific research. The invention of the camera dates back to the 19th century and has since evolved with advancements in technology, leading to a vast array of types and models in the 21st century.
A rangefinder camera is a camera fitted with a rangefinder, typically a split-image rangefinder: a range-finding focusing mechanism allowing the photographer to measure the subject distance and take photographs that are in sharp focus. Most varieties of rangefinder show two images of the same subject, one of which moves when a calibrated wheel is turned; when the two images coincide and fuse into one, the distance can be read off the wheel. Older, non-coupled rangefinder cameras display the focusing distance and require the photographer to transfer the value to the lens focus ring; cameras without built-in rangefinders could have an external rangefinder fitted into the accessory shoe. Earlier cameras of this type had separate viewfinder and rangefinder windows; later the rangefinder was incorporated into the viewfinder. More modern designs have rangefinders coupled to the focusing mechanism so that the lens is focused correctly when the rangefinder images fuse; compare with the focusing screen in non-autofocus SLRs.
A view camera is a large-format camera in which the lens forms an inverted image on a ground-glass screen directly at the film plane. The image is viewed and then the glass screen is replaced with the film, and thus the film is exposed to exactly the same image as was seen on the screen.
A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the lenses is the photographic objective or "taking lens", while the other is used for the viewfinder system, which is usually viewed from above at waist level.
In optical engineering, an objective is an optical element that gathers light from an object being observed and focuses the light rays from it to produce a real image of the object. Objectives can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.
A movie projector is an opto-mechanical device for displaying motion picture film by projecting it onto a screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras. Modern movie projectors are specially built video projectors.
An enlarger is a specialized transparency projector used to produce photographic prints from film or glass negatives, or from transparencies.
Macro photography is extreme close-up photography, usually of very small subjects and living organisms like insects, in which the size of the subject in the photograph is greater than life size . By the original definition, a macro photograph is one in which the size of the subject on the negative or image sensor is life size or greater. In some senses, however, it refers to a finished photograph of a subject that is greater than life size.
In photography, a viewfinder is a small window the photographer looks through to see what a photo will look like before they capture it.
A digital single-lens reflex camera is a digital camera that combines the optics and the mechanisms of a single-lens reflex camera with a solid-state image sensor and digitally records the images from the sensor.
Laboratory flasks are vessels or containers that fall into the category of laboratory equipment known as glassware. In laboratory and other scientific settings, they are usually referred to simply as flasks. Flasks come in a number of shapes and a wide range of sizes, but a common distinguishing aspect in their shapes is a wider vessel "body" and one narrower tubular sections at the top called necks which have an opening at the top. Laboratory flask sizes are specified by the volume they can hold, typically in metric units such as milliliters or liters. Laboratory flasks have traditionally been made of glass, but can also be made of plastic.
Video assist is a system used in filmmaking that allows filmmakers to view and distribute a video version of a take immediately after it is filmed. On set, the location where the assist is reviewed is called a video village.
Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may be rapidly fitted together to reflux a reaction mixture. This is a large improvement compared with older methods of custom-made glassware, which was time-consuming and expensive, or the use of less chemical resistant and heat resistant corks or rubber bungs and glass tubes as joints, which took time to prepare as well.
The Mamiya RZ67 is a professional medium format single-lens reflex system camera manufactured by Mamiya. There are three successive models: the RZ67 Professional, RZ67 Professional II and RZ67 Professional IID. It is primarily designed for studio use, but can also be used in the field.
The stereo, stereoscopic or dissecting microscope is an optical microscope variant designed for low magnification observation of a sample, typically using light reflected from the surface of an object rather than transmitted through it. The instrument uses two separate optical paths with two objectives and eyepieces to provide slightly different viewing angles to the left and right eyes. This arrangement produces a three-dimensional visualization of the sample being examined. Stereomicroscopy overlaps macrophotography for recording and examining solid samples with complex surface topography, where a three-dimensional view is needed for analyzing the detail.
The design of photographic lenses for use in still or cine cameras is intended to produce a lens that yields the most acceptable rendition of the subject being photographed within a range of constraints that include cost, weight and materials. For many other optical devices such as telescopes, microscopes and theodolites where the visual image is observed but often not recorded the design can often be significantly simpler than is the case in a camera where every image is captured on film or image sensor and can be subject to detailed scrutiny at a later stage. Photographic lenses also include those used in enlargers and projectors.
The Panasonic Lumix DMC-GH1 is a digital mirrorless interchangeable lens camera adhering to the Olympus and Panasonic developed Micro Four Thirds System (MFT) system design standard. Panasonic classified the GH1 as a hybrid stills/video camera and the GH1 was introduced and marketed as a higher end camera than Panasonic's first MFT camera, the stills only, non-video capable Lumix DMC-G1.
This article was originally based on "Ground glass back" in Camerapedia, retrieved at an unknown date under the GNU Free Documentation License.