Slide (photography)
A slide film , slide film (from ancient Greek δία dia , German 'through' ) or reversal film is a photographic film that, after its development, shows gray values or colors in a natural view.
After developing and cutting the film, individual slides are created that are often used for projection.
The reversal technique is also used for motion picture films when no screening copies have to be made. For a long time, reversal film was used almost exclusively in the amateur sector ( Normal 8 , Super 8 ). It was also used for television reports ( 16 mm film ) from the beginning of television in the 1950s to the introduction of electronic reporting in the late 1970s. In the cinema, on the other hand, negative film and copies are used (→ film editing ).
Heyday
In the second half of the 20th century, reversal films found mass circulation. At that time they represented a way for amateur photographers to produce color pictures in a cheap way. Despite the ability to take color photos from negatives - and nowadays photos from digital data - reversal film has always held its own. Its strength is the high contrast range compared to paper prints .
The preferred form of presentation of slides is projection. This peculiarity is so typical that it is used in the form of the "slide show" in computer presentations. Paper prints are also possible from slides , but the color slide optimized for projection has a high contrast range that can often only be reproduced on paper to a very limited extent.
In 2001, reversal films had a share of 7% of the 187 million films sold in Germany. However, demand had already declined in previous years.
The slide was also at home in the cinema . For decades the ideal format was in use on the cinema slide format 85 mm × 85 mm. The same light was used for projection as for the moving image, so there were still projectors with lime light , pure coal and Beck-coal arc lamps .
Footage and development
Black and white reversal films have a mixed image layer of two different emulsions . One approach is highly sensitive, mostly panchromatically sensitized, the other unsensitized and less sensitive. When taking the pictures, the low-sensitivity silver salt remains underexposed by about ten times. After the first developer has developed a negative from the more sensitive silver salt, it is bleached, i.e. H. converted into a soluble compound, and then dissolved out of the image layer. The remaining salt is then completely exposed, blackened in a further developer bath ( second or positive developer ) and the further usual treatment. The addition of the negative is now a fine-grain positive.
Color reversal films are now built up as multilayer films that are processed using a chromogenic process . The basic development corresponds to the black and white reversing process. The first developer is a powerful black and white developer. It reduces all exposed silver salt crystals to elemental silver. They have no part in the further development of the picture. The first development is interrupted by a stop bath, further processing takes place in the light. In the subsequent intermediate exposure, the remaining silver salt is completely exposed. During color development, the dyes are created on the reduced silver salt crystals via the color couplers . The topmost, blue-sensitive layer is yellow, the one below, green-sensitive, purple and the bottom, red-sensitive, blue-green. By reducing all of the silver, the film now appears almost black. The color development is followed by the bleach bath, which converts all silver back into soluble silver salts. The positive image becomes visible, but it is still clearly too dense due to the silver salts. The fixer dissolves all silver salts from the emulsion, what remains is the dye image. Color reversal films are now developed using the standardized E-6 process.
The Kodak Kodachrome reversal film had a similar film structure with completely different processing : the color couplers were not located in the light-sensitive layers. Rather, the three emulsion layers were individually subjected to reverse development in the course of processing in the K-14 process, with corresponding color couplers for each base color being in a separate developer solution. This process, which has remained largely unchanged since its introduction in 1935, enables particularly thin light-sensitive layers, which leads to greater sharpness - for decades Kodachrome reversal films were superior to all other color reversal materials in terms of their sharpness. Kodachrome reversal films could de facto only be developed at Kodak due to the complicated K-14 process. Kodak offered this service until the end of 2010.
In the past few years, other films have caught up. Currently (as of 2015) the Fujichrome Provia 100F (normal color matching, extremely neutral gray balance) and the Fujichrome Velvia 50/100 / 100F (color-enhanced, for nature and landscape photography) are considered to be the sharpest and finest-grain reversal films in the world. What is remarkable is the fine grain, sharpness and color saturation of the Fujichrome Provia 400x (discontinued), which on the basis of these parameters draws level with the 100 ASA emulsions of the late 1990s.
The basic structure of reversal films and negative films is the same. As a result, the reverse development of a negative film or negative development of a reversal film is basically also possible ( cross development ). The achievable results are more likely to be described as "experimental". For example, for special applications and effects, color reversal film can also be developed using the C-41 process, which is actually intended for color negative films . The result is high-contrast negatives with overly saturated colors. The negative development of black-and-white reversal films, however, should not provide any useful results, since these films, like color reversal films, mostly have an antihalation layer consisting of colloidal silver, which is only removed in a bleach bath during a color process.
Most black and white films are negative films, not reversal films. Exceptions were the black and white reversal films Agfa Scala , Fomapan R and the Agfa DD (Dia-Direct), which had not been produced for a long time . In principle, any black and white negative film can be developed into slides by reverse development (cross development: in the SCALA process, reverse development according to Wehner), but good results can only be achieved with films that have a colorless base (e.g. Agfa Copex Rapid, ADOX CMS 20 II, Agfa Scala). Black and white films for negatives usually have a gray base , which prevents halos from developing . In the meantime, there are methods for producing black and white slides that can elicit suitable films with up to 800 line pairs per mm of resolution, which is far more than with color reversal films.
Slides can also be created by copying negatives onto positive film . Both contact copies and optical copies are possible. In the theatrical film production this method is used almost exclusively. The disadvantage of a contact copy is the different layer status. In the case of reversal films, the layer support faces the viewer (or the projection lamp), in the case of contact copies the layer side. This change in position of the image can lead to a change in focus during projection, which even projectors with automatic focusing cannot compensate for. Reverse and contact copy slides should therefore not be mixed for projection. Optical copies are also often made in this way. In the case of optical copies, the loss of sharpness of an additional generation of copiers has a disadvantageous effect.
Slide viewing
The size of a 35 mm slide (36 mm × 24 mm) is too small to be able to view it without any tools. There are therefore slide viewers in which the slide is viewed through a magnifying glass. Ambient light or a small incandescent lamp is usually used for lighting . In such viewers, both framed slides and uncut film strips can usually be viewed. Slide viewers are also available in versions as stereo slide viewers .
With the help of slide projectors , the slides can be projected onto a screen or focusing screen. As a rule, the individual slide must be framed.
Slide show
In the years of the millennium, the mass spread of digital photography began. This was accompanied by the possibility of viewing digital photos in a convenient way on the computer screen; for example as an independently running sequence of images. For this type of picture presentation, the name “slide show” became established. A stylized slide is often used as a symbol. The stylization usually shows a framed slide with a triangle inside (= "rendering").
Advantages and disadvantages of reversal film
Basics of contrast range
The greatest difference in contrast in our everyday life is between the dead of night and blazing sunshine. One speaks here of a large contrast range. There is no image system that can fix the complete contrast range of nature in one image. Therefore, the natural range of contrast of a subject must be reduced before the image is saved.
Of all - non-digital - imaging methods , a slide has the greatest contrast range and the greatest contrast differentiation .
A general comparison with the digital imaging methods is difficult because there are no representative comparison tests.
The slide has the greatest contrast range (contrast 1: 1000) - the pressure one of the lowest. The print must not be confused with a real photo (contrast 1: 100) .
A general comparison with the digital imaging methods is difficult because there are no representative comparison tests.
The practical advantages of reversal film are primarily the high sharpness and color fidelity as well as the large tonal range of the slide. These properties of the reversal film are clearly evident in the projection. The image quality of a projected 35mm slide has a high contrast range and differentiation.
Transfer with reduction of the contrast range
The reduction of the natural contrast range in reversal and negative film is tailored to the respective purpose (projection or photo). If a photo (contrast 1: 100) is to be made from the slide (contrast 1: 1000), the contrast range of the slide must be significantly reduced. There are various technologies for this:
-
Reversal paper
- The basic principle works like a print from a negative , only that normal photo paper is not used. The result looks a bit dull (soft contrast, low color saturation).
-
Intermediate negative
- Using suitable methods ( camera attachment , contact copy , ...) the slide is photographed. A negative is created . A normal print is made from this. The result is good, but uneconomical due to the high workload.
- Agfa digiprint
- This procedure was introduced in the 1990s. The slide is scanned, optimized and then exposed on normal photo paper. The optimization software suppresses "unimportant" contrast information, severely restricts the range of contrast and adapts the contrast impression ( hardness of the contrast , overemphasis on certain colors, unsharp masking, ...) to regional viewing habits. For this purpose, the software is trained during operation . With professional software calibration (laboratory-dependent), the result gives a high quality impression and is well suited for amateur use.
-
Ilfochrome (formerly Cibachrome)
- Ilfochrome is a special photo paper that is used in a similar way to reversal paper. However, the result is of significantly better quality. This fact is based on three properties: lighter white, darker black and excellent contrast behavior.
- The special white and black ensure a significantly larger contrast range. This is still below that of a slide, but above that of normal photo paper.
- The contrast behavior creates a very good optimization effect .
- An additional compression of the tonal values can be achieved with contrast masks. A black and white negative is exposed using the contact method in such a way that the subsequent addition with the slide results in the desired contrast range.
- Ilfochrome is an expensive material and has therefore never caught on in the mass market.
- Ilfochrome is a special photo paper that is used in a similar way to reversal paper. However, the result is of significantly better quality. This fact is based on three properties: lighter white, darker black and excellent contrast behavior.
-
Digitization (scanning)
- This is the latest technology. The basic principle is similar to that of the Agfa Digiprint process. The difference lies in two properties:
- Agfa-Digiprint was a self-contained process. It could only be used for slides on the input side and only deliver photos on photo paper on the output side (it was not possible to save the scan on a data carrier ). Digitization, on the other hand, is an open process.
- The scanner and optimization software is much more sophisticated and ubiquitous these days; Film scanners are also available for home users at moderate prices. Technologies such as multi-exposure help to preserve as large a part of the contrast range of the original as possible.
- The exposure of digital data is nowadays inexpensive and of high quality. Therefore, the digitalization of slides for the production of prints is becoming more and more popular. Our viewing habits have adapted to this fact. In addition, dust and scratches can be detected during digitization using the scanner's infrared sensor and removed from the digital image.
- This is the latest technology. The basic principle is similar to that of the Agfa Digiprint process. The difference lies in two properties:
quality
If high-quality slides are projected properly, one can get a good impression of the natural color and brightness during the recording situation. The quality of this visual impression still marks a quality standard for other imaging methods . Basically, however, the quality of the film material decreases over time due to environmental influences. Often discolored or faded images result. Glass-framed slides show a particularly high loss of quality because Newton's rings , for example , can arise.
Slides were used in the professional sector until the 1990s, since their quality was easier to assess than that of negatives.
- Example: After a fashion shoot, not only should the image motifs be compared with one another, but the quality of the representation of the fabric colors should also be assessed. If the slides were placed side by side on a light table , that was straightforward. If you had instead photographed on negative material and made prints from it, only a comparison of motifs would have been possible. The exact assessment of the fabric colors would not have been possible (due to the omnipresent image optimization). In addition, finding the right negative would have been added as a further step, with hundreds of relatively similar motifs a Sisyphean task .
Archiving
Most of the slides are unique ; Duplicate slides are rarely used. In general, unique items are exposed to a comparatively high risk, as damage from dust, fingerprints, scratches, light and moisture is irreversible. Since slides have a gelatin layer, they are, like all other photographic materials, susceptible to fungi and bacteria (especially behind glass-framed pictures). In the course of years, holes and mold can form and the slide will be destroyed.
It is possible to duplicate or digitize slides. Problems with:
- Duplication of slides is an analog process, so it is always associated with a loss of quality.
- If high-quality slides are scanned with as much information as possible, file sizes of several hundred megabytes (with 16-bit color depth ) can quickly arise. It is also difficult to find a suitable imaging method for displaying this mass of data (contrast range, contrast differentiation, color range). With the advancement of computer technology , it is now also possible for home users to use slide scanners to create a digital archive of their own slide collection. Alternatively, slides can also be commissioned from numerous service providers for digitization.
Today's reversal film market
Color reversal films
All manufacturers of chemical photographic materials have suffered since 2001 from the decline in demand in favor of digital photography. Of the former three large reversal film manufacturers Kodak , Agfa and Fuji , only the Japanese Fuji was able to successfully restructure its business model. Other manufacturers were ORWO , Konica , Foma and Ferrania .
In November 2004, Agfa-Gevaert spun off the film and photo paper division into AgfaPhoto, which filed for bankruptcy in May 2005. AgfaPhoto Holding GmbH, which is not affected by the insolvency, has since acted as a licensor of trademarks, not as a manufacturer. This means that there have been no Agfachrome reversal films from our own production since 2005 .
In March 2007 the Japanese company Konica Minolta completely stopped the production of photochemical films and papers. With this, the Konica reversal films (Konica Chrome, Konica Sinbi) disappeared from the market.
The Italian company Ferrania (until 1996 part of the 3M group) ended film and photo production (e.g. Solaris reversal films and many commercial brands) in 2011, and bankruptcy began in 2004.
Kodak discontinued the famous Kodachrome reversal film in June 2009 due to falling demand and high costs. Kodak filed for bankruptcy in January 2012, followed by the cessation of production of all remaining Kodak reversal films ( Ektachrome , Elite Chrome) in March 2012.
Until 2017, only the Fujifilm Corporation was active as a manufacturer of color reversal films. In July 2012, the Fuji reversal film range was significantly reduced ( Fujichrome Velvia and Fujichrome Provia).
Kodak Alaris brought a new edition of the "Ektachrome E100", a new edition of the Ektachrome color reversal film, onto the market in 2018.
Black and white reversal films
A black and white reversal film from the Czech manufacturer Foma is available under the name Fomapan. From ORWO a recording film (UN 54) is provided, which as a negative or positive film can be developed. Fotoimpex, founded in 2006, now has five different black and white films on offer with the Adox brand (as of 2020) that can be developed as slides using the Scala process (SCALA 50 BW, SCALA 160 BW, HR50, SILVERMAX, CMS 20 II) . In addition to the films from Adox, there are also films from the Ilford brand on the market that are basically suitable for this process.
See also
- Slide projector
- Slide scanner
- Transparency attachment
- Slide duplicator
- Slide frame
- Analog photography
- Assembly
- Film speed
- Film cartridge
- Color photography
- Chronology of Photography
Web links
- Afgfa Precisa 100 / E6 slide film in direct comparison to digital photography using the example of Cologne Cathedral Photos with overexposure and underexposure illustrate dynamics, contrast and colors.
Individual evidence
- ↑ a b 35mm color films: color known - Stiftung Warentest . From test.de , accessed on November 24, 2012.
- ↑ Slide films: Kodachrome 25 disappears - Stiftung Warentest . test.de , accessed on November 24, 2012.
- ↑ Dust and scratch correction when digitizing slides. Retrieved on February 10, 2018 (German).
- ^ A new era , Agfa-Gevaart website, company history, accessed on November 18, 2012.
- ↑ Insolvency Poker for AgfaPhoto , Photoscala article, accessed on November 18, 2012.
- ↑ Fotowirtschaft, Edition 12/2009 ( Memento of the original from January 12, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , AgfaPhoto website (PDF; 2.4 MB), accessed on November 18, 2012.
- ↑ AgfaPhoto is threatened with collapse , article in Der Spiegel, accessed on November 18, 2012.
- ↑ discontinuation of photo chemistry, cameras and binoculars , manufacturer's website, accessed on November 23, 2012.
- ^ Adieu, Kodachrome , Article of Photoscala, accessed on November 18, 2012.
- ↑ Kodak is broke , article in the Süddeutsche Zeitung, accessed on November 18, 2012.
- ↑ Kodak ends an era , article on n-tv.de, accessed on November 18, 2012.
- ↑ "Falling demand": Fujifilm streamlines film range , article from the creative network dasauge, accessed on November 18, 2012.
- ↑ Color slide film range , Fuji website, accessed November 18, 2012.
- ↑ Kodak Alaris. Retrieved December 26, 2018 .
- ^ Black and White Film Assortment - Foma , Foma website, accessed November 18, 2012.
- ↑ ORWO universal negative film UN 54 - technical information. ORWO FilmoTec GmbH, August 1, 2010, accessed on October 30, 2016 .
- ↑ Photo Studio 13: Scala development 2019. In: Photo Studio 13 - Stuttgart. Retrieved August 15, 2020 .
