Prepressforums.com

richsweeney · #1 (**permalink**) 08-30-2003, 08:47 PM

We are using 150 line screen and realized we could be doing 200. Does any one have any tip or tricks, and is it worth it.

cari · #2 (**permalink**) 08-31-2003, 08:47 AM

The screen ruling you use depends mainly on the stock on which you will be printing ajob

Examples
Newsprint 85lpi - 100lpi
Magazine 120lp -175lpi

Before going to 200lpi I would consult with the printer printing the jobs you are outputting, and you might find they'd not want higher than 175lpi.

#3 (**permalink**) 09-02-2003, 06:26 AM

A additional question to that subject is does the chance of angle clash increase by using a finer screen ruling?

cari · #4 (**permalink**) 09-02-2003, 10:14 AM

this answer is NOT based on facts, so I could be wrong! I'm trying to source from the "grey" cells here... -- if someone has factual info please add --

I'd say the answer to your question is yes and no... Yes, because in a certain area you'd have more dots, which would equal more clash options technically speaking. No, because as the dots are smaller it becomes less visible (i.e. optical = less, technical=more)...

Angle clash occurs at all screen frequencies and depends on the screen angle each of the individual colours will have. The clash is minimal (this is conventional prepress talk b.t.w.) when the screen angles vary 30-degrees... In 4-colour process you'd run out of "angles", hence the yellow (being the lightest of the 4 colours) being set to 90-degree angle, with the other 3 colours printing at 15, 45 and 75-degrees.

To avoid angle clashing you could opt to use FM-screening/Stochastic-screening, which uses a "scattering" pattern of similar sized dots.

Hope I haven't totally confused everyone!

Vinny · #5 (**permalink**) 09-05-2003, 09:05 AM

I've been playing around with line screens over the last few months. I use 133 lpi Agfa Balanced Screening for just about all my uncoated and coated spot color work.

I have tried 175 lpi on high quality uncoated cover stock with good results but our poor little didde webcom with 2 ink form rollers could hardly stand it. Anything with 4 color I use 150 lpi for uncoated and 175 lpi for coated.

I do believe alot of it depends on what kind of press your printing to. For instance our Didde Webcom couldn't handle 200 lpi very well at all. The shadows would plug up pretty bad.

I've heard people say they can't see a difference with 175 compared to 200.

Seth · #6 (**permalink**) 10-01-2003, 11:28 AM

Be aware also that high screen rulings require precise calibrations in both electronics and chemistry (if using film). An 85line screen is nice and coarse, variations in the process will have little effect on dot reproduction and linearity. Kick that ruling up to 200 or so, and a variation in the process can have visible effects.

As to the 'Sceen angle clash' -- yes a finer (higher) screen is more susceptible to moir?. However, pre-sceened artwork is rarely seen by my shop nowadays. Digital source files are un-screened.

If you're doing Flexography, then screen angles have to compensate for the roller angles. This can be touchy with high value screens. But, few flexographers would be doing high screen rulings.

-Seth

richsweeney · #7 (**permalink**) 11-29-2003, 08:41 AM

After having long talks with various pressman, It sounds like only on a really good 4 color press should be running 175 line or higher, and that press should be well maintained. I don't think we would have any problem in the pre-press part, but is sounds like it gives the pressmen a smaller range to work within. We are only running a 2 color ManRoland.

JanZ · #8 (**permalink**) 12-02-2003, 07:52 AM

We have offset presses and run:

175 line for 4c on coated stock
150 line for 4c on uncoated stock
150 line for spot color on coated stock
133 line for spot color on uncoated stock
85 line for 'quick print' jobs using plastic plates

We run process jobs with higher line screens to give a more visually pleasing finished product.

But remember that the higher the line screen, the more dot gain on press. Also uncoated stocks have more dot gain than coated stocks.

Jan

Eyetech · #9 (**permalink**) 04-18-2004, 03:33 AM

Screening at 200lpi takes a good deal longer than our standard 175lpi on our ECRM Mako 56. So if you have a lot of thru'put it may be a factor.

Careful tho' if you've a job with tinted areas, say 60c or 100c 80m, go to press with that at 200lpi and then run the same at 175lpi the tints won't necessarily match

We had this happen on a monthly newsletter we produce usually at 200, we were short of time so we ran the film at 175 and whoops! nowhere near the original colour values.

But the other posters are quite right, you need a good press to keep a 200lpi screen 'open'