The bare minimum you’ll need in order to ouput your own film is an imagesetter, RIP, and processor. A system of these three components will allow you to produce your own positives or negatives from your computer in the following steps:

1 – RIPs are designed to accept PostScript files. Some RIPs can also accept PDF files. You’ll need to generate a PostScript or PDF file from your application program (such as Quark, Pagemaker, Illustrator, etc) and then print this file to the RIP.

2 – The RIP will translate your file into a bitmap and add screening, and then send the file to the imagesetter.

3 – The imagesetter will output your file to film.

4 – After imaging, you will need to remove the imagesetter takeup cassette or dropbox and take it to the processor for developing. The processor will develop and dry the film. You will now have finished film, ready for burning a plate

While the imagesetter, RIP, and processor are the only essential items for outputting film, there are other pieces of equipment you should consider for controlling output quality. These items include a transmission densitometer (to calibrate the imagesetter) and a color proofer.

The imaging principle of capstan imagesetters is similar to that of typewriter. With capstan imagesetters, there is a roller that advances the media through the imaging area. The laser is fixed, and a mirror or prism distributes the laser beam across the media to image it as it advances.

With drum imagesetters, the film is held stationary onto the drum while the imaging head moves along a spindle to expose the film.

Because there is less movement involved during imaging, there is less possibility for error, and the output from drum imagesetters has better registration than the output from capstan imagesetters. While the majority of capstan imagesetters can produce good process color, it does not equal the output from a drum imagesetter.

Whether you should choose a capstan or drum imagesetter depends on your budget, output size requirements, and quality requirements. Capstan imagesetters are usually less expensive than drum imagesetters. Except for a few machines, such as the ECRM Stingray 63 and the PrePress Panther Pro 62, most capstan imagesetters output 2up or 4up. If you need larger output sizes such as 8up, you’ll probably need a drum imagesetter. However, it is important to keep in mind that you are restricted to outputting the maximum format of the drum with drum imagesetters. With capstan imagesetters, you can output the width of the film by much longer lengths. So, if you need to output long galleys, a capstan device would be a good choice. Finally, if you require perfect registration, a drum imagesetter is the way to go.

There are four different types of imagesetter lasers

Infrared (IR) 780 nanometers
Visible Red (VR) 650 - 680 nanometers
Helium Neon (HeNe) 633 nanometers
Argon Ion (AI) 488 nanometers

Nanometers refer to the wavelength on the color spectrum. 488 is in the blue range, 633 to 680 is in the red range, and 780 is in the infrared range and not visible to the eye. 488 and 633 nanometer lasers are gas lasers based upon argon ion and helium neon gases respectively. Visible red and infrared lasers use laser diode technology.
The original laser technology evolved from the high-end scanner recorder systems used by the color shops that preceded the PostScript technology we know today. The first imagesetters were based exclusively upon argon ion or HeNe gas laser technology borrowed from scanner/recorder technology. Eventually, technology and design improved enough that imagesetters were able to produce process color jobs.
It did not take long for competition to develop a less costly architecture than that of gas laser based machines. This was the infrared laser diode. Although this technology created lower cost imagesetters, they were not competitive in quality. The major problem with infrared lasers is that they produce a “soft” dot. This dot could not measure up to the uniformly hard dot created by gas lasers. The soft dot created increased dot gain that must be compensated for in the platemaking and printing process.
Another factor affecting acceptance of infrared based machines was the added cost of the film. As nanometer sensitivity of film increases so does its cost of production.
It was not until the development of the visible red laser diode that quality became competitive with the gas laser architecture. The visible red laser diode solved both the soft dot problem and the film cost problem plaguing the infrared diode technology. As a result of lower production cost, comparable film cost, and comparable quality, the visible red laser diode has become the dominant laser technology used in imagesetters.
BWI recommends anyone considering an imagesetter purchase choose a machine that utilizes a HeNe or visible red laser. Infrared machines are considered obsolete. Film for these machines is difficult to obtain, and costs considerably more than film for HeNe/Visible red machines.

A transmission densitometer is used to calibrate an imagesetter to ensure that it is producing dots accurately. Whether you need one depends on the type of work you plan to produce. If you will only do black and white or spot color printing, a transmission densitometer is a good thing to have, but not absolutely required. If you plan to output process color, a densitometer is essential.
When outputting process color, your imagesetter will produce 4 separate films for each of the process colors – cyan, magenta, yellow, and black. These films are then used to burn 4 separate plates. The quantity of ink deposited by the press for each color is determined by the size and density of the dots on each plate. If the imagesetter creates dots incorrectly, the colors of the final printed product will not match those in your original file or digital proof.
To a lesser degree, dot percentage (size) can also be a factor for quality black and white images. If the dots created by the imagesetter are too large, the image will darken and begin to lose detail in the dark, or shadow, areas. If the dots are too small, the image will appear too light and detail will be lost in the white, or highlight, area.
A transmission densitometer is used in conjunction with a calibration utility program supplied with most RIPs to calibrate the imagesetter. First, through the RIP, a test strip with patches of dot percentages from 0% to 100% is output and then developed. Using the densitometer, the actual percentage of each patch is read, and the readings are entered into the calibration program. For example, the imagesetter should print patches of 10%, 20%, and 30% on the calibration strip, but the actual percentages printed might be 14%, 25%, and 36%.
After entering the actual readings into the calibration programs, the RIP will adjust the imagesetter’s output so the dot percentage printed is closer to that requested by the RIP. Another output of the dot percentage matrix should then be created, and procedure repeated until the dot percentage created by the imagesetter is reasonably close to what it should be for each of the patches audited.

There are 2 types of processors available for use with imagesetters – online and offline. The offline processor is a standalone unit. The online processor hooks up directly to an imagesetter, through a buffer, bridge, or conveyor. Online processors are usually not used with smaller output devices, such as 12-14” capstan devices and 2up drum imagesetters. If you are looking at a larger system (4up or 8up), you might want to consider an online processor. There are several advantages to an online processor over an offline processor. These include:

-Increased productivity. With an online processor, the film goes directly from the imagesetter into the processor and comes out developed, dry, and ready to use. If you have an online processor, the imagesetter will output to a takeup cassette. This cassette must be removed and taken over to the processor for developing. Unless you purchase extra takeup cassettes, the imagesetter will be idle while the film is developing in the processor.
-Less manual trimming is involved. With an online processor, you can have the imagesetter cut after each plate, or after each job, and continue outputting. When outputting to a takeup cassette, you have to remove the cassette and develop the film after each cut.
-Eliminate the need for a darkroom. Most imagesetters output to a takeup cassette that will fit in the daylight feed box of offline processors. These imagesetters and processors can be used in a daylight environment. However, there are some imagesetters that output to a dropbox, not a cassette. In order to develop the film, it must be removed manually and fed into a processor. In these cases, the processor must be in a darkroom. When used with an online processor, though, the entire system can be used in a daylight environment. Imagesetters that use a dropbox include the Scitex Dolev 200, 400, and 800 series.

Are there advantages to using an offline processor? The main advantage of the offline processor is cost. An offline processor is usually much less expensive than the online processor. Further, if you have 2 imagesetters, you can use one processor to develop film from both. Also, if you still use a camera, you can put an offline processor in the darkroom and use it develop film from both the imagesetter and the camera.