DX coding
The DX coding ( DX stands for Digital indeX ) is defined as ANSI PH1.14 and I3A standardized, coded, electrically readable markings on the cartridges of photographic films .
functionality
The coding contains information about film speed , exposure latitude and film length , among other things . Some of the information is used for camera control, another for laboratory processing. Since these are automation functions, the photographer normally does not come into contact with the DX coding.
The DX code comprises the following components:
- Checkerboard code (CAS) on film cartridge ;
- Bar and numeric code on the film cartridge;
- Information field on the film cartridge;
- Barcode on the edge of the film for color negative films .
The outer packaging of DX-coded films usually shows a “DX” or “DXN” symbol to indicate the presence of a corresponding coding.
Checkerboard code
The CAS code (for Camera Auto Sensing Code) called the checkerboard pattern of the DX coding on 35mm films in 135 format is used to control the camera; the information contained is read out automatically by most automatic cameras and taken into account during exposure. However, older or simple camera models only read the film speed.
The code consists of a total of 12 fields in two rows, which are either conductive (silver or blank (here white in the illustration); codes a logical 1) or non-conductive (black or coated; codes a logical 0), so that the corresponding Contacts on the camera are bridged or not; the information is therefore coded in binary .
The upper row contains fields 1 to 6 from left to right, and the lower row contains fields 7 to 12. The cartridge must be viewed in such a way that the film slot is visible upwards and the winding core is visible on the left.
| Film slot | ||||||
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4th | 5 | 6th | |
| Winding core | Mass ( common ) | Film sensitivity ( film speed ) | ||||
| Number of exposures ( exposure counts ) | Exposure latitude ( Exposure Tolerance ) | |||||
| 7th | 8th | 9 | 10 | 11 | 12 | |
The DX-iX coding for APS films (film format IX240 aka Advantix) consists of considerably more fields and stores - in accordance with the APS specifications - additional information.
Film speed
The film speed is in the DX encoded defined in 1/3 EV steps between # 25/15 ° and ISO 5000/38 °; however, film speeds above ISO 1600/33 ° usually have to be set manually on the camera. In addition to the 24 predefined values, 8 further values are available for special settings (one for each sensitivity group), but these are not interpreted at all by most cameras or are interpreted in different ways.
Particularly simple cameras can also work with a reduced number of contacts for reading out the film sensitivity. Is z. For example, if the exposure latitude of typical negative films is used, contact fields 1 to 4 are sufficient for a rough detection of the sensitivity in whole steps. If you restrict the supported area, only contact fields 1 to 3 are required. If a distinction is only to be made between two permitted sensitivities, only two contacts are necessary.
| ISO | 1 | 2 | 3 | 4th | 5 | 6th |
|---|---|---|---|---|---|---|
| 25/15 ° | ||||||
| 32/16 ° | ||||||
| 40/17 ° | ||||||
| 50/18 ° | ||||||
| 64/19 ° | ||||||
| 80/20 ° | ||||||
| 100/21 ° | ||||||
| 125/22 ° | ||||||
| 160/23 ° | ||||||
| 200/24 ° | ||||||
| 250/25 ° | ||||||
| 320/26 ° | ||||||
| 400/27 ° | ||||||
| 500/28 ° | ||||||
| 640/29 ° | ||||||
| 800/30 ° | ||||||
| 1000/31 ° | ||||||
| 1250/32 ° | ||||||
| 1600/33 ° | ||||||
| 2000/34 ° | ||||||
| 2500/35 ° | ||||||
| 3200/36 ° | ||||||
| 4000/37 ° | ||||||
| 5000/38 ° | ||||||
| Special 1 | ||||||
| Special 2 | ||||||
| Special 3 | ||||||
| Special 4 | ||||||
| Special 5 | ||||||
| Special 6 | ||||||
| Special 7 | ||||||
| Special 8 |
Film length
The film length or frame number ( receiving number ) is in the DX encoded with 12, 20, 24, 36, 48, 60, and 72 shots (coding for "non-standard" is also available) defines and is encoded with three bits .
| Recordings | 7th | 8th | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|
| other length | ||||||
| 12 | ||||||
| 20th | ||||||
| 24 | ||||||
| 36 | ||||||
| 48 | ||||||
| 60 | ||||||
| 72 |
Exposure latitude
The exposure latitude is in the DX encoded defined with ± 1/2 aperture ± 1Blende, + 2 / + 3 -1 aperture and / -1 aperture.
| Margin (in EV ) |
7th | 8th | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|
| ± ½ | ||||||
| ± 1 | ||||||
| + 2 / -1 | ||||||
| + 3 / -1 |
example
The film cartridge shown here has the following DX coding (the barcode is not taken into account):
Fields 1, 3 and 6 (starting at the top left in the figure) are conductive, so the film speed is ISO 125/22 °; fields 7, 8 and 9 (starting at the bottom left in the figure) are conductive, so the film has 24 frames; the last two fields are also conductive, so the film has an exposure latitude of + 3 / -1.
Barcode
The barcode contains processing information for copiers; it includes information about the processing process, the type of film, film sensitivity and film length.
Color negative films can also be provided with a barcode on the edge of the film, which contains a product identification; this information is also only relevant for automated film processing in photocopiers.
History and Development
The method of DX coding developed by Kodak for film format 135 was introduced on January 3, 1983 ( Kodak Press Announcements 1-83-1425 and 1-83-1427) in order to simplify the handling of 35 mm films . In contrast to earlier isolated solutions, such as the 135 cartridge system introduced by Fujifilm in 1977 with electrical contacts for detecting film sensitivity, Kodak's DX code quickly found widespread market acceptance.
The first film to use DX code was Kodacolor VR-1000, a color negative film introduced in March 1983 . Today, most 35mm films are DX-coded, only products from Eastern European countries , Russia or Asia often lack this coding.
The Konica TC-X single-lens reflex camera is considered to be the first 35 mm camera to use the DX code . Pentax takes the title of the first non-SLR camera with DX support for the Pentax Super Sport 35 (PC 35AF-M) from 1984 and the title of the first SLR camera with DX code support for the A3 / A3000 from 1985 in claim. The first Minolta cameras with DX code support were the AF-E / Freedom II compact camera introduced in July 1984 and the Minolta 7000 AF introduced in February 1985 . At Nikon, this function was also introduced in 1985 with the F-301 / N2000.
An extended variant is DX-iX (data exchange - information exchange), which was introduced with the Advanced Photo System in 1996 and is used exclusively for APS films (film format IX240 aka Advantix).
Since around 1998 an identification system similar to the DX code has also been available for roll films in formats 120 and 220, which was introduced by Fujifilm under the designation barcode system . The film format and length, the film speed and the film type are coded in a barcode on the sticker that connects the light-sensitive film with the carrier paper. This barcode can be read by some newer medium format cameras.
See also
Individual evidence
- ^ Matthias Paul: Detailed information on the DX / CAS code . Article dated October 22, 2005 (Retrieved July 21, 2011).
- ↑ Fuji: US Patent 4024557: Film magazine having film speed indicating means In: Google Patents (accessed July 21, 2011).
- ↑ Amateur Photographer: "Fuji's Latest Auto-System", February 16, 1977, page 61 (scan of the article: JPG TIF , accessed July 21, 2011).
- ^ Pentax: "1984: Pentax introduces its second leaf-shutter sport model, the Super Sport 35 (PC 35AF-M). The new addition offers all of the features of the Sport 35, plus a built-in auto winder, fully automatic loading and automatic film speed setting using the Kodak-pioneered DX coding system. The Super Sport 35 is the world's first non SLR camera to incorporate the DX film sensing system. " ( Memento of the original from March 28, 2012 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. . In: History of Innovations / History of Innovations (Accessed July 21, 2011).
- ↑ Pentax: "1985: The Pentax A3000, a fully automatic SLR, is introduced. Its automated features include: exposure, film loading and winding, and film speed setting with DX-coded film. The A3000 was the world's first 35mm SLR camera to utilize the DX film sensing system. This new SLR also allows for creative flexibility with features such as: aperture-priority, backlight compensation and a 12-second self-timer. The camera's Pentax KA bayonet lens mount makes it compatible with more than 50 Pentax lenses. " ( Memento of the original from March 28, 2012 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. . In: History of Innovations / History of Innovations (Accessed July 21, 2011).
- ↑ Konica Minolta: Note on the presentation date of the Minolta AF-E / Freedom II in July 1984 ( memento of March 23, 2008 in the Internet Archive ) . In: Minolta camera story on the Japanese Konica Minolta website.
- ↑ Konica Minolta: Note on the presentation date of the Minolta 7000 AF in February 1985 ( Memento from March 23, 2008 in the Internet Archive ) . In: Minolta camera story on the Japanese Konica Minolta website.
- ^ Matthias Paul: Information on barcodes on roll films . Article dated August 24, 2008 (accessed July 21, 2011).
Web links
- How is the DX coding structured? (Photo FAQ by Mark Paede)
- Overview of the various DX codes