Harlequin Dispersed Screening on a DPX Genesis

[discountprintingservice]

Hello,
I have a DPX Genesis polyester platesetter that I bought from another print shop which is running with a Ripmate 4.2 rip. The previous owner had bought the HDS screening plug-in but apparently never used it. I don't have much literature on the use of it.

I am running 8 mil polyester in the machine, and the Mitsubishi trained tech tells me this capstan device is only capable of up to 133 line screen at 1800 dpi. But according to the specifications the device's resolution is 600-2400 dpi, and the laser specs are as follows:
Ir-Laser Diode 760 nm, 1 mW
Spot size 35 um

So my question is what HDS Screening should I use and at what dpi? my choices are HDS Fine, HDS Medium, HDS Coarse, HDS Super Coarse, and HDS Super Fine

I don't understand the correlation between each of these setting and spot size or dpi.

For example:
If I use HDS Medium at 1200, 1800, & 2400 dpi what would the equivalent lpi be?
Same question for the others also....
And if my spot size is 35 um which HDS at which dpi am I limited to using with my DPX Genesis?

Ideally I would like to be able to print around a 200 lpi equivalent....

Also, my reason for wanting to use the HDS is so I can produce 4 color process with more detail than conventional 133 line screen, which I plan to run on my 13x18 portrait 2 color press.

Is or has anyone used a DPX Genesis (Genesis only not other DPX systems) to produce quality 4 color?

Any help here would be greatly appreciated!

 

[gordo]

You can always experiment to see if you like what you get (which I doubt).

HDS Super Coarse uses a larger structure to increase printability and the capability to retain highlighted areas of an image. It is suitable for use on mid to low-range imagesetters or platesetters with resolutions between 1000 and 1600 dpi. 
The spot sizes in microns using a 20% screen are: 1200 dpi - 84 microns, 1800 dpi - 56 microns, 2400 dpi - 42 microns

HDS Coarse. The spot sizes in microns using a 20% screen are: 1200 dpi - 51 microns, 1800 dpi - 34 microns, 2400 dpi - 26 microns

HDS Medium. 1200 dpi - 42 microns, 1800 dpi - 28 microns, 2400 dpi - 21 microns

HDS coarse has a resolution equivalent of about 275 lpi and an equivalent lithographic ruling of about 205 lpi.

Your laser spot size of 35 microns is about the same size as a 1% dot at 70 lpi.

You are probably not going to be able to use HDS screening. However you might try a different technique to increase your apparent lpi. The rosette structure that forms in 4/C process screen tint builds reduces the effective lpi visually by half. In other words a rosette at 133 lpi will look like a 70 lpi structure. If you use heavy GCR for your color separations you will lessen the likelihood of rosettes forming and will minimize this effect.

You will need to experiment.

best, Gordo

 

[discountprintingservice]

Thanks for the reply....

but I am curious...why would HDS been sold as an option with the Genesis if the spot size was not capable of it?

I see newspapers printed with FM, i would have thought that if 133 looked good I could use fm and make it look better than 133...i don't quite understand

 

[gordo]

Thanks for the reply....

but I am curious...why would HDS been sold as an option with the Genesis if the spot size was not capable of it?

I see newspapers printed with FM, i would have thought that if 133 looked good I could use fm and make it look better than 133...i don't quite understand

Yes many newspapers are printed with FM - typically 25 or 35 micron FM. The rough and absorbent newsprint paper tends to soften and hide the somewhat large dots. On coated paper the dots will be better defined and hence more visible.

Your laser spot size is capable of doing FM, however, the spot size limits the size of the smallest halftone dot you can image. It might limit you to an FM screen that is coarse enough that it will not be visually better than a 133 lpi screen. This is a matter of personal taste which is why you need to do a bit of comparative testing. (You might try 150 lpi instead.)

The other caveat is that your system may not be capable of consistently imaging an FM screen on plate. Small dots/finer screens are simply more challenging on the process.

best, gordo

 

[BillJ]

The Genesis maximum screening is actually 127 lpi that in interpolated to 133.

 

[idrivepos]

HDS screens

HDS screens

These screens on the Gen HQ rip are for an Epson printer.
Never intended for plates.
The Genesis is a crude entry level machine optimized for 127 lpi (133)
the rip can do higher but the platesetter can not.
I would not advise printing 4/c off this machine, fit problems...
it was designed for 1 color- 2 color.