Enlarger

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Scheme of a photographic enlarger. Darkroom enlarger en.svg
Scheme of a photographic enlarger.

An enlarger is a specialized transparency projector used to produce photographic prints from film or glass negatives, or from transparencies.

Photography Art, science and practice of creating durable images by recording light or other electromagnetic radiation

Photography is the art, application and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed in many fields of science, manufacturing, and business, as well as its more direct uses for art, film and video production, recreational purposes, hobby, and mass communication.

Negative (photography) Image on photographic film

In photography, a negative is an image, usually on a strip or sheet of transparent plastic film, in which the lightest areas of the photographed subject appear darkest and the darkest areas appear lightest. This reversed order occurs because the extremely light-sensitive chemicals a camera film must use to capture an image quickly enough for ordinary picture-taking are darkened, rather than bleached, by exposure to light and subsequent photographic processing.

Reversal film type of photographic film that produces a positive image on a transparent base

In photography, reversal film is a type of photographic film that produces a positive image on a transparent base. The film is processed to produce transparencies or diapositives instead of negatives and prints. Reversal film is produced in various sizes, from 35 mm roll film to 8×10 inch sheet film.

Contents

Construction

All enlargers consist of a light source, normally an incandescent light bulb, a condenser or translucent screen to provide even illumination, a holder for the negative or transparency, and a specialized lens for projection. The light passes through a film holder, which holds the exposed and developed photographic negative or transparency.

Incandescent light bulb Electric light with a wire filament heated until it glows

An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated to such a high temperature that it glows with visible light (incandescence). The filament is protected from oxidation with a glass or fused quartz bulb that is filled with inert gas or a vacuum. In a halogen lamp, filament evaporation is slowed by a chemical process that redeposits metal onto the filament, thereby extending its life.

A condenser is an optical lens which renders a divergent beam from a point source into a parallel or converging beam to illuminate an object.

Photographic film sheet of plastic coated with light-sensitive chemicals

Photographic film is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film.

Prints made with an enlarger are called enlargements. Typically, enlargers are used in a darkroom, an enclosed space from which extraneous light may be excluded; some commercial enlargers have an integral dark box so that they can be used in a light-filled room.

Darkroom workshop used by photographers make prints and otherwise handle photographic film

A darkroom is used to process photographic film, to make prints and to carry out other associated tasks. It is a room that can be made completely dark to allow the processing of the light-sensitive photographic materials, including film and photographic paper. Various equipment is used in the darkroom, including an enlarger, baths containing chemicals, and running water.

Types of enlarger

Photographic enlarger. Enlarger-bogen.jpg
Photographic enlarger.

A condenser enlarger consists of a light source, a condensing lens, a holder for the negative and a projecting lens. The condenser provides even illumination to the negative beneath it.

A diffuser enlarger's light source is diffused by translucent glass or plastic, providing even illumination for the film.

Photon diffusion is a situation where photons travel through a material without being absorbed, but rather undergoing repeated scattering events which change the direction of their path. The path of any given photon is then effectively a random walk. A large ensemble of such photons can be said to exhibit diffusion in the material, and can be described with a diffusion equation.

Condenser enlargers produce higher contrast than diffusers because light is scattered from its path by the negative's image silver; this is called the Callier effect. The condenser's increased contrast emphasises any negative defects, such as dirt and scratches, and image grain.

Contrast (vision) difference in luminance and/or color that makes an object distinguishable

Contrast is the difference in luminance or colour that makes an object distinguishable. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view. The human visual system is more sensitive to contrast than absolute luminance; we can perceive the world similarly regardless of the huge changes in illumination over the day or from place to place. The maximum contrast of an image is the contrast ratio or dynamic range.

Callier effect

The Callier effect is the variation in contrast of images produced by a photographic film with different manners of illumination. It should not be confused with the variation in sharpness which also is due differences partial coherence.

Diffuser enlargers produce an image of the same contrast as a contact print from the negative. [1]

Dedicated color enlargers typically contain an adjustable filter mechanism - the color head - between the light source and the negative, enabling the user to adjust the amount of red, green and blue light reaching the negative to control color balance. Other models have a drawer where cut filters can be inserted into the light path, synthesize colour by additive mixing of light from colored lamps with adjustable intensity or duty cycle, or expose the receiving medium sequentially using red, green and blue light. These enlargers can also be used with variable-contrast monochrome papers.

Digital enlargers project an image from an LCD screen at the film plane, to produce a photographic enlargement from a digital file. [2]

Enlarger physical arrangements

Most modern enlargers are vertically mounted with the head pointing downward and adjusted up or down to change the size of the image projected onto the enlarger's base, or a work table if the unit is mounted to the wall.

A horizontal enlarger consists of a trestle, with the head mounted on crossbars between two or more posts for extra stability. A horizontal enlarger structure is used when high quality, large format enlargements are required such as when photographs are taken from aircraft for mapping and taxation purposes.[ citation needed ]

The parts of the enlarger include baseboard, enlarger head, elevation knob, filter holder, negative carrier, glass plate, focus knob, girder scale, timer, bellows, and housing lift.

Principles of operation

Enlarger lens: using the diaphragm - aperture ring the photographer adjusts the iris. Enlarger lens board.jpg
Enlarger lens: using the diaphragm - aperture ring the photographer adjusts the iris.

The image from the negative or transparency is projected through a lens fitted with an adjustable iris aperture, onto a flat surface bearing the sensitized photographic paper. By adjusting the ratio of distance from film to lens to the distance from lens to paper, various degrees of enlargement may be obtained, with the physical enlargement ratio limited only by the structure of the enlarger and the size of the paper. As the image size is changed it is also necessary to change the focus of the lens. Some enlargers, such as Leica's "Autofocus" enlargers, perform this automatically.

An easel is used to hold the paper perfectly flat. Some easels are designed with adjustable overlapping flat steel "blades" to crop the image on the paper to the desired size while keeping an unexposed white border about the image. Paper is sometimes placed directly on the table or enlarger base, and held down flat with metal strips.

The enlargement is made by first focusing the image with the lamp on, the lens at maximum aperture and the easel empty, usually with the aid of a focus finder. The lamp is turned off, or in some cases, shuttered by a light-tight mechanism.

The image is focused by changing the distance between the lens and the film, achieved by adjusting the length of a light-tight bellows with a geared rack and pinion mechanism. [3]

Electric timer: photographers choose exposure time. Darkclocks.JPG
Electric timer: photographers choose exposure time.

The lens is set to its working aperture. Enlarging lenses have an optimum range of apertures which yield a sharp image from corner to corner, which is 3 f/ stops smaller than the maximum aperture of the lens. For an enlarging lens with a maximum aperture of f/2.8, the optimal aperture would be f/8. [4] The lens is normally set to this aperture and any color filtration dialed in, if making a color print or one on variable-contrast black-and-white paper.

The enlarger's lamp or shutter mechanism is controlled either by an electronic timer, or by the operator - who marks time with a clock, metronome or simply by counting seconds - shuttering or turning off the lamp when the exposure is complete. The exposed paper can be processed immediately or placed in a light-tight container for later processing.

Digitally controlled commercial enlargers typically adjust exposure in steps known as printer points; twelve printer points makes a factor of two change in exposure.

In June 2017, an iOS app called enLARGE was launched on the Apple AppStore which for the first time allowed the accurate computation of the exposure time required to expose a larger enlargement, eg 16x20”, based on the exposure time found to be correct for the production of a much smaller pilot enlargement made first, from the same negative, at a smaller size such as wallet-print, thus making the production of the larger enlargement quicker and more economical. The same app also allowed, for the first time, the easy production of perfectly matching enlargements of different sizes, from the one negative, without the need for individual exposure retesting for each differently sized enlargement; up until this time enlargements were typically made at only one predetermined size.

Paper processing

After exposure, photographic paper is developed, fixed, washed and dried using the gelatin silver process.

Automated print machines

Automated photo print machines have the same basic elements and integrate each of the steps outlined above in a single complex machine under operator and computer control.

Rather than project directly from the film negative to the print paper, a digital image may first be captured from the negative. This allows the operator or computer to quickly determine adjustments to brightness, contrast, clipping, and other characteristics. The image is then rendered by passing light through the negative and a built-in computer-controlled enlarger optically projects this image to the paper for final exposure.

As a byproduct of the process a compact disc recording may be made of the digital images, although a subsequent print made from these may be quite inferior to an image made from the negative due to digitization noise and lack of dynamic range which are characteristics of the digitizing process.

For better images, the negatives may be reprinted using the same automated machine under operator selection of the print to be made.

Advantages

Image enlargement limits

Adjusting elevation knob: change in image size. Enlarger height and printing size.svg
Adjusting elevation knob: change in image size.

The practical amount of enlargement (irrespective of the enlarger structure) will depend upon the grain size of the negative, the sharpness (accuracy) of both the camera and projector lenses, blur in the image due to subject motion and camera shake during the exposure, and the intended viewing distance of the final product.

For example, a 5 by 7 inch print intended for viewing in a scrapbook at 18 inches may be unsuitable for enlargement as an 8 by 10 inch print to be hung on a hallway wall to be viewed at the same distance, but usable at a larger 5 by 7 feet (twelve times larger) on a billboard to be viewed no closer than eighteen feet (twelve times more distant).

Manufacturers

As the photographic market shifts away from film-based towards electronic imaging technology, many manufacturers no longer make enlargers for the professional photographer. Durst, who made high quality enlargers, stopped producing them in 2005, but still supports already sold models. Manufacturers old and new include:

See also

Notes

  1. Established in pre-WW2 Stuttgart, moved to UK in 1938, closed in 1994 [6]

Related Research Articles

Camera Optical device for recording images

A camera is an optical instrument to capture still images or to record moving images, which are stored in a physical medium such as in a digital system or on photographic film. A camera consists of a lens which focuses light from the scene, and a camera body which holds the image capture mechanism.

Exposure (photography) amount of light captured by a camera

In photography, exposure is the amount of light per unit area reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.

Camera lens optical lens or assembly of lenses used with a camera body and mechanism to make images of objects

A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.

Photographic paper paper coated with a light-sensitive chemical formula, used for making photographic prints

Photographic paper is a paper coated with a light-sensitive chemical formula, used for making photographic prints. When photographic paper is exposed to light, it captures a latent image that is then developed to form a visible image; with most papers the image density from exposure can be sufficient to not require further development, aside from fixing and clearing, though latent exposure is also usually present. The light-sensitive layer of the paper is called the emulsion. The most common chemistry was based on silver salts but other alternatives have also been used.

Overhead projector device that projects a transparent image

An overhead projector (OHP), like a film or slide projector, uses light to project an enlarged image on a screen. In the overhead projector, the source of the image is a page-sized sheet of transparent plastic film with the image to be projected either printed or hand-written/drawn. These are placed on the glass surface of the projector, which has a light source below it and a projecting mirror and lens assembly above it. They were widely used in education and business before the advent of computer-based projection.

LCD projector type of video projector

An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector. To display images, LCD projectors typically send light from a metal-halide lamp through a prism or series of dichroic filters that separates light to three polysilicon panels – one each for the red, green and blue components of the video signal. As polarized light passes through the panels, individual pixels can be opened to allow light to pass or closed to block the light. The combination of open and closed pixels can produce a wide range of colors and shades in the projected image.

Unsharp masking A technique for sharpening digital images

Unsharp masking (USM) is an image sharpening technique, often available in digital image processing software.

Contact print photographic image produced from film

A contact print is a photographic image produced from film; sometimes from a film negative, and sometimes from a film positive or paper negative. In a darkroom an exposed and developed piece of photographic film or paper is placed emulsion side down, in contact with a piece of photographic paper, light is briefly shone through the negative or paper and then the paper is developed to reveal the final print.

Photographic printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transparency , or a digital image file projected using an enlarger or digital exposure unit such as a LightJet printer. Alternatively, the negative or transparency may be placed atop the paper and directly exposed, creating a contact print. Photographs are more commonly printed on plain paper, for example by a color printer, but this is not considered "photographic printing".

Dodging and burning

Dodging and burning are terms used in photography for a technique used during the printing process to manipulate the exposure of a selected area(s) on a photographic print, deviating from the rest of the image's exposure. In a darkroom print from a film negative, dodging decreases the exposure for areas of the print that the photographer wishes to be lighter, while burning increases the exposure to areas of the print that should be darker.

The science of photography refers to the use of science, such as chemistry and physics, in all aspects of photography. This applies to the camera, its lenses, physical operation of the camera, electronic camera internals, and the process of developing film in order to take and develop pictures properly.

Gum bichromate

Gum bichromate is a 19th-century photographic printing process based on the light sensitivity of dichromates. It is capable of rendering painterly images from photographic negatives. Gum printing is traditionally a multi-layered printing process, but satisfactory results may be obtained from a single pass. Any color can be used for gum printing, so natural-color photographs are also possible by using this technique in layers.

The following outline is provided as an overview of and topical guide to photography:

Köhler illumination is a method of specimen illumination used for transmitted and reflected light optical microscopy. Köhler illumination acts to generate an even illumination of the sample and ensures that an image of the illumination source is not visible in the resulting image. Köhler illumination is the predominant technique for sample illumination in modern scientific light microscopy. It requires additional optical elements which are more expensive and may not be present in more basic light microscopes.

Dye transfer is a continuous-tone color photographic printing process. It was used to print Technicolor films, as well as to produce paper colour prints used in advertising, or large transparencies for display.

The digital negative is the collective name for methods used by photographers to create negatives on transparency film for the contact printing of alternative photographic techniques. The negatives can also be enlarged using traditional gelatin silver processes, though this is usually reserved for negatives of 4x5" or larger due to quality limitations imposed by printer technology. This set of techniques is separate from the Digital negative (DNG) file format, although this format may be used to create digital negative transparencies.

References

  1. "Diffuser vs Condenser Enlargers". Applications Printing In Black & White Darkroom Equipment. Ilford Photo. Archived from the original on July 21, 2015. Retrieved October 4, 2015.
  2. "De Vere 504 DS Digital Enlarger". Odyssey Sales. Archived from the original on 6 September 2004. Retrieved 21 September 2015.
  3. "Black and White World's Enlarger Guide" . Retrieved 2008-07-29.
  4. Jacobson, Ralph E. (2000). "6 - Optical aberrations and lens performance". The manual of photography : photographic and digital imaging (9th ed.). Boston, Mass.: Focal Press. p. 80. ISBN   978-0-240-51574-8.
  5. "Gnome Photographic Products". www.gracesguide.co.uk. Retrieved 9 April 2018.
  6. "Gnome Pixie". The Camera Shelf. Retrieved 4 October 2015.