Over the years, many different types of microfilm have been used to store many different types of records. First, a high level review of the types of film.
Many companies did not follow good practices or standards when making the original film years ago, so quality is often bad. Users often hate using film, because retrieval is time consuming and the poor quality makes the documents difficult to read. Therefore, as the alternatives of electronic imaging become more economical than microfilm, many companies are moving to the new technology. See the separate paper on microfilm conversion available at www.plesums.com/image/filmconv.html
Traditional roll microfilm is 16 mm wide, with a film image that is 1/24 of the size of the original document, often called 24x. Images are normally side by side on the film, like a comic book, so a letter size image is a little over 1/3 inch wide, and a ledger sheet can be well over 1/2 inch. (In some systems the film images are above and below each other on the roll, like a movie. This is called cine format - as in cinematography - rather than comic fomat.) A typical 100 foot roll of film contains about 2,000 to 2,400 images, but shorter rolls are common as the film was removed and processed at the end of the day or week.
Some cameras adjust the magnification so that the resulting images of various size documents are about the same size. If the camera "zooms out" to get a legal size document in the same area of film as a letter size document, the magnification may be about 32x instead of 24x, and when output the document will be slightly smaller, but on letter size paper. But some facilities realized they could leave the camera at 32x, and get 3,200 pages on the same roll that ordinarily held 2,400 pages. The reader/printer must adjust to this size, or the output will be smaller when printed.
Some cameras and computer output systems creates an image 1/42 or 1/48 of the document original size, with a few systems using even smaller or larger sizes. A 48x image is half as wide as a 24x image, so there could be twice as many images along the roll of film. Further, since the images are also only half as high, sometimes the roll is "turned over" and more images are recorded on the other side of the film (called "duo... format - duplex format indicates that the front and back of a page are next to each other). Therefore 10,000 images could be on a roll of 48x film or several hundred pages on a 48x computer output microfiche.
Some vendors promoted a film that was half as thick as usual, so twice as much could be stored on a standard roll. With double length film (actually 215 feet rather than 100 feet on the same size roll), a 24x roll could have over 6,000 images, and a 48x roll could have about 25,000 images. With smaller documents such as checks and receipts, even more images are possible on a roll. This thinner film is fragile and did not feed well in some equipment, so was rejected by many companies. Other companies have adjusted their equipment and developed procedures for handling the thinner film, and have made extensive use of it.
Some cameras have a set of mirrors that allow the front and back of a document to be captured at the same time (duplex), with the back often placed above the primary image as the roll moves side to side. In indexing and conversions the front and back are often treated as a single image that can be cut into separate pages later in the process.
A rotary camera moves individual pages through the "camera" holding the lens still, and moving the film in synchronization with the paper. These units were fast, and the width of the image was proportional to the width of the document. A "step and repeat" camera is used to photograph microfiche - the film is moved though various steps corresponding to the frames on the fiche, and a stationary picture is taken. A planetary camera holds both the paper and film in a fixed position during exposure, and is often used for bound documents - it takes a picture of each page after it has been laid flat on the bed of the camera. The camera is often set up to photograph a larger area (big enough for a ledger sheet), with the same film image often created for even a small document. These images need to be trimmed (cropped) when they are retrieved or converted. If they are not trimmed, and the whole area of the camera bed is printed on a single sheet of paper, the resulting image may be far smaller than usual. (There is a rule of legal evidence that the image must be reproduced to approximately the original size.) Some organizations wrote the operator name and date on the camera bed, above the document being filmed, as additional information about the film image.
Positive or Negative?
Original microfilm is often negative - dark background with light print
Copies made using diazo (ammonia) technology retain the polarity - a copy of a negative will remain negative.
Copies made using vesicular (heat) or ordinary silver technology change polarity - a copy of a negative will be positive, and vice versa.
A special process can be used with silver copies to maintain polarity. If multiple generations of copies are required, this produces better results.
Negative microfilm is often preferred because dust is hidden by the dark background, but is very obvious on positive film. Most reader-printers convert either to positive images when printed.
A blip (mark) is often exposed near the edge of the film to mark where each page is located. Roll film readers automatically count the blips to find a particular page. Small, medium, and large blips designate "page", "chapter", and "book" (in a business environment, normally interpreted as page, document, and folder).
When the roll is full (or at the end of the day or week) the film is processed. The issues of managing and using a wet chemical process in an office environment has led many companies to use an "outside" service company for the processing, or to struggle with various "dry" processes. Normal film processing produces a negative image (dark background with light text). Full reversal processing involves some extra steps which produce a positive image on the same film, the same as the original image, which from the camera would be clear "white" background and black print.
As soon as the film is processed, whether in-house or by a service bureau, the quality of the film should be checked - both for camera issues like focus, and processing issue such as density. After confirming the quality of the film, a working copy should immediately be created and the original should be sent directly to the environmentally controlled archive. Note that if normal processing is used, the negative original becomes a positive working copy.
If the image will remain on the roll of microfilm, an index must be created for each document, so the document can be located. For example "The correspondence from customer 23456 is on roll 1234 starting at frame 345." The index for the roll film is often called a Computer Assisted Retrieval (CAR) system, or from Kodak they are often called a KAR system. Older systems were typically a CICS program to access a mainframe relational database or ISAM file. These databases have often been converted to network servers or even personal computer systems in the records area.
In many companies users can access the CAR system directly to see what documents are known, and request specific documents. Companies moving away from film may have users request "all" documents for a customer or case from the records area, so only the records area uses the CAR system to locate individual documents.
For retrieval, the CAR system may create a list of documents required, sorted by roll, so all the documents can be retrieved from the roll while it is mounted. The operator finds and mounts the correct roll and enters the frame number on the console. The reader automatically searches for the specified frame. In practice, the reader-printer will quickly get within a few frames of the one desired - some blips will be missed, or a smudge of dust could be interpreted as an extra blip, so the search will be close but often not exact. Errors in indexing can also lead to the wrong number of blips to reach a specific document.
The operator checks the position of the film, adjusts the location on the roll, trims the edge of the image (zooms in) to recreate the size of the original document, adjusts the light/dark, then prints the desired pages. Consecutive pages on a roll are likely to be similar, so printing the following pages goes quickly (since the camera, lighting, and chemicals were the same), but the adjustments are likely to be different between different rolls. The next document for this customer is likely to be on a different roll - documents that arrive at different times are not normally together on the same roll of film.
Early reader-printers used the light going through the film to actually create the copy, leading to bulky units that were relatively slow as the mirrors redirected the light from the screen to the copier. (Besides being difficult to maintain mechanically, these early units require more, and more expensive, supplies.) Newer reader-printers capture the image with digital scanner technology, so they can use cheaper personal-computer laser printers. Since the image is digital, some of these newer units even allow documents to be transferred to an image system, or to be cached so that related documents can be printed together.
If frequent access is required to the film, copies of the entire set of film are sometimes placed in the user area. A purchased copy of a roll of film typically only costs about $5 to $8. Three or more copies are common:
Jackets are plastic sleeves in which small pieces of film, representing individual document (cut from roll microfilm) are inserted. "All" the documents for a particular contract or policy are placed in a single jacket, much like a file folder.
Each 105 x 148 mm (4 x 6 inch) jacket typically has 5 horizontal rows, with an opening at the right end of each row where the film is inserted. Each row can hold 10-15 pages. With narrow documents some rows occasionally have as many as 18 pages. Most companies start a new row if, for example, a three page document arrives and there is only space for one or two pages in the current row. Therefore the beginning of a row is more likely to have the beginning of a document, a fact useful in indexing. Although a single jacket can hold up to about 70 pages, several companies have found that the average is about 50 pages per jacket.
The "indexing" consists of the customer, contract, or account number written on the jacket, and inserting the film in the right jacket, but there is no identification of the individual documents. Traditionally the jackets are filled chronologically, left to right, top to bottom, but even this is not required.
Since the little pieces of film can slide out of the jacket, some facilities make a copy of the entire jacket for any use outside of the records area. The cost of a quick "sandwich" copy is in the 15-25 cent range, and takes only a few seconds. The copies may be returned to the records center for recycling or security reasons, but generally cannot be reused since additional documents could have been added to the jacket.
Since different documents were likely filmed and inserted at different times, with different processing, film density and quality varies from document to document. The pages are imperfectly aligned, especially single page documents where the tiny chip of film may be substantially skewed. The variation in quality and alignment in a fiche are no problem for a casual viewer, but a challenge for automated conversions.
Obsolete terminology used the phrase "Archive Quality" to mean data that could be kept forever; anything less than forever was not archive quality. The more realistic "Life Expectancy" rating, abbreviated LE, is now used. Only properly processed and correctly stored silver halide film on polyester base has an LE rating of 500 years (LE 500), whereas acetate based silver halide film (no longer commercially available) can have LE ratings of 100 years.
To achieve that long life expectancy, the original microfilm must be kept in special temperature/humidity controlled environment, in special sealed containers, and must only be used to make working copies. Generally no more than five working copies should be made from that first generation master from the camera - if more copies are required, they should be made from a working copy.
A few companies keep their masters in an air conditioned room, but I have never seen a business that follows all the requirements for full life expectancy. Too many companies don't keep their master film in a controlled environment at all - and in far too many cases, the only original is used as the working copy. Storing and using microfilm so that it will have the expected long life is not cheap or easy.
Only working copies of roll film should be used in viewers or reader/printers. A copy is made by pressing the light-sensitive emulsion of the unexposed film against the processed emulsion of the original film, and exposing it to a light - a contact copy. (Quality is lost if the copy is not made with emulsion against emulsion.) The original film "reads right" when viewed from the shiny base side of the film, with the emulsion on the outside of the roll. The first generation copy "reads right" when viewing the dull emulsion side of the film, with the shiny base on the outside of the roll. Stated another way, the delicate emulsion is on the back of the original but is on the front of the copy. (A copy of a copy would again place the emulsion on the back.) Reader/printers are designed to minimize the wear on the front of the film, assuming that the film is a working copy, not the original. An original should never be placed in a viewer, since the wear will be concentrated on the delicate emulsion.
Electronic imaging is currently the low-cost way of storing and retrieving business documents. But this has not always been the case. For many years microfilm was the storage media of choice, so many companies have a large amount of microfilm (roll and fiche) that is part of their records storage.
If there is little or no retrieval of the film that has already been created, the space and staff to maintain the records on film is probably far cheaper than any conversion. However, the cost of retrieval is far greater from film, so many companies are converting their microfilm. The table below compares the cost of various steps in the life of roll film, jacket microfiche, and digital images.
|Roll Film||Microfiche||Digital Images|
|Capture||equipment, staff, supplies||equipment, staff, supplies||similar but no supplies|
|Indexing||computer entry||insert film in jackets||computer entry|
|Storage||space and staff||space and staff||primarily computer, occasional copies|
|Retrieval||Several dollars per document||a dollar per file||pennies|
|Purge||almost impossible||trivial for simple purge||flexible|
Every company with older documents on microfilm and newer documents on a digital document image system faces some choices:
Microfiche is the alternative to roll microfilm. It comes in two flavors. Computer output microfiche is generated directly from a computer system, each page is perfectly aligned and organized in column sequence. COM is neat, but customer files are far more likely to be on the "jacket" type microfiche.
The original microfilm reader-printers were a type of copier - the light shining through the film was used directly to make the printed copy. These reader-printers were large, slow, and mechanically complex (often out of adjustment). The only output was paper, so use of these machines to convert an image requires two steps - printing (conversion from film to paper), and scanning (conversion of paper to an electronic image). The two steps require extra time, labor, and supplies, and reduces quality by doing two image conversions.
Newer reader-printer technology actually scans the film digitally, and uses a personal-computer style laser printer to make the printed copy. Many of these newer machines have an option to export the image electronically rather than just printing it. That electronic image can then be imported into the document image system. The capital cost of the feature to export the digital image is relatively small, and the conversion is performed in one step, with better quality, taking less labor and materials. Although this technology is now available to digitally scan a particular document from either roll film or fiche, it is very labor intensive, so it is far better to use high speed film scanners when dealing with large numbers of documents.
Microfilm records can include some problems that cannot be fixed by a conversion. In some cases, these problems are so severe that there may be no solution under any circumstances. For example, potential problems include:
Many years ago "good practice" included using a white background when filming documents on white paper. The later printed copies had little or no border, so were "pretty." However, there is also no way to find the edge of the original document, so no assurance that the copy will be approximately the size of the original (as required for evidence). Current "good practice" includes using a dark background, which allows automatic or manual trimming to the edge of the original document.
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