One of the most significant steps ever taken in the continuing evolution of PostScript color production must include the internal drum recorder. This article published some time ago is interesting because the material is pertinent to the present state of the art.
The main issue we found, when comparing various drum recorders, (or for that matter capstan imagesetters) is the light source. Readers who have been users of Linotronics over the past ten years will recall that most Linotronic imagesetters such as the L300 and L500 series featured a Helium-Neon light source. This changed with the release of the Linotronic 630 which in an about face to previous offerings, featured a laser-diode light source. Since that time with the L830 and L930, there have been changes once again, to the use of the Argon-Ion Laser with emission at 488 nanometers.
On the other hand, Agfa who were competitors when the Linotronic 630 was introduced took a contrary view and concluded that helium-neon would be the better medium for their SelectSet 5000/7000 series.
Of course these machines, though widely used to this day are in 2003, being replaced by recorders that use any of the three basic laser types running on platforms that are faster in production but not necessarily more accurate.
Which method is best? That is for you to decide! In my mind you will have to trust the designing engineers to use the appropriate device.
"If we presume for the moment that all laser light is coherent and powerful enough to create a hard dot on film and assuming that your film is tuned for the characteristics of the laser. There is no validity to the claim that a laser diode, or a helium-neon laser or for that matter an argon-ion laser, will deliver a different shape dot on film. In fact laser light is so coherent that it can produce too hard a dot, making it difficult for dot etchers. In fact some years ago, other companies, for example Crosfield, actually added noise to their diodes to make the dot softer."
"We have laser diode, helium-neon and argon light sources in our product line and we have generated good quality film output from all three light sources using tuned materials. Examination under an electron microscope proves that under optimal conditions each light source can generate a hard dot. If you can take that leap of faith, then the question is, why not use a laser diode? There is every reason in the world to use a laser diode, because of the fact that it is a solid state device, does not require complex optical systems and shuttering mechanisms such as are required in the case of helium-neon. In addition the laser diode is very compact and can therefore be mounted on the carriage providing some distinct advantages."
"We mount the laser diode on the carriage, because this gives us a very short, simple, optical path. If you look at the mechanisms of a laser diode machine, you will see that the laser diode and the rotating mirror, are less than an inch apart. This rotating prism deflects the light source once, ninety degrees, onto the photographic material. The distance from the laser diode to the film remains constant over the entire imaging area, whereas in the case of HeNe recorder, the helium tube is mounted below the drum making it necessary for the light source to be deflected four times before it reaches the film."
"The reason the helium-neon light source is mounted below the drum, is because a helium-neon tube is way too large and complex to mount on the spindle. In addition, there are many more corrections to make. Each time the light source is diverted, increases the need for more precision and fine tuning, (which also raises the question as to whether it will be possible to maintain those tolerances over a period of time)."
"Most of the criticisms leveled against laser diode has been mainly focused upon the imaging material, not the light source. Now, what is special about the laser featured in laser-diode machines such as the Linotronic L630, is that it's sensitivity is not in the infra-red range like most laser diodes, but in the helium-neon range. Basically, we have the advantages of helium-neon material which is more stable and of lower cost and the means to operate with a shorter optical path.
In the case of lasers used, (prior to the Linotronic 630), there is some difficulty in maintaining an even density over the full width of an image. In the case of the Linotronic 630 and later Hercules, the density is even across the whole width of the imaging material."
"The major reason for creating the light source used in the Linotronic 630 was to maintain simplicity. Every time you deflect your light source, you have to be sure that you are deflecting it accurately, since each error in each mirror, or deflection magnifies itself. Error corrects itself if you are lucky, But usually you are not lucky, especially in the real world environment where you have jitter and vibration on the machine. You have to be sure that a machine will be able to produce the same high quality three years from now!"
"Some competitors have predicted that mounting the laser diode on the lead screw compounds the "wobble characteristic". In answer to this I would suggest that consideration should be given to the fact that Linotype-Hell have a very, very, high quality reputation based upon lead screw technology, a principal which has been employed all along, not only by Hell, but also by D.S.Screen and Crosfield."
"There are a number of other areas where we feel the Linotronic 630 has a number of advantages. For example, the Linotronic 630 is probably the most economical imagesetter with respect to film use. We have features on our imagesetter that do not exist anywhere else, built into the unit specifically for saving film. To load the Linotronic 630 with film requires less than an inch of material, compared to 6 to 8 inches to load other machines. The Linotronic 630 has gear driven supply cassettes which allows us to retract the film that is not going to be imaged. So if you decide to change your material from a twelve inch material to an eighteen inch material, very little material is wasted."
"However, if I went from 12" to 18" material on our main competitor's machine, wastage could run from 22" to 26" on the wider machine. This material is wasted because they are unable to retract the material back into the supply cassette. On the other hand, on the Linotronic 630 I can execute a command that will retract the material back into my supply cassette, saving some $4.00 to $5.00 on each occasion!"
"Most manufacturers now move their materials on a cushion of air to eliminate scratches, jamming and static build-up. In the Linotronic 630 we go a step further and provide for a positive airflow on the material so that there's a completely flat imaging point with no air bubbles under the film. Recognizing this solution to a nagging problem with air bubbles and pops underneath the material, has prompted our competitors to modify their more recent releases, which raises the question, "what about those people who have already bought a new drum recorder?"
Note: Linotronic-Hell products are now sold by Heidelberg Canada.
Comparison of Drum Recorders and Light Sources