It's right here:
http://murakamiscreen.com/wp-content/uploads/2012/07/HalftoneAnglestopreventmoire.pdf
I can only hope I missed something, but it's amazing to me that it's being implied that a halftone angle change is capable of magically fixing the thread occlusion moire going on here...
When you say "going on here", I'm assuming you're referring to Gilly's original issue of the moire.
The screen "angle" comments are 2ndary to his real issue (to me in my opinion) is obvious.
The main issue is the fact he's using 55lpi halftone on low mesh. The "general rule of thumb" as Frog pointed out is all math. Using between 4 and 5, (I prefer 5. will help guide you in a proper mesh to halftone selection.
150 mesh, divided by 4 = 37.5 line screen.
150 mesh, divided by 4.5 = 33 line screen.
150 mesh, divided by 5 = 30 line screen.
At the most, we should be using 38 line screen on a 150 mesh (when you want your fade to go all the way out without interference.
Can you use a higher line screen? Sure, many do, but many lose those small dots. At best, they get that jagged edge at the end where you see what looks saw toothed. That is the mesh blocking out the last few percentages of dots. This is so common that it's accepted as par for the course. I might not even fight it that much or re burn a screen at a lower line count in my own shop it's so common (if I saw that). It's not "bad" per say, just not optimum.
Here in Gilly's post, this is an extreme case and is why he's inquiring about it. He knows it aint right. Its a case where you do not want to be and leave your shop (in my opinion). This says to other printers,
my shop made an error and let it go. Thats how I see this stuff (if I say it on a person). I think it says to the average buyer, (something looks wired on that but I can't put my finger on it).
So, with that said, someone might say, "so you would use
that big of a dot?" No. I wouldn't. I would bump up my choice of screen mesh and use a finer dot that matches that.
Then adjust how I print it so I still get the needed coverage.My goal in a gradation (100% to 0%) is to maintain holding all dots as much as possible. Given that I can print
most of my jobs on a 230 or higher, I would start there. If I wanted to use 55lpi for sure, it would go like this.
230 mesh, divided by 4 = 57.5 line screen.
230 mesh, divided by 4.5 = 51 line screen.
230 mesh, divided by 5 = 46 line screen.
I would not use anything lower than a 45 line screen on a 230 mesh. 55 is as high as I go and that is pushing it due to the fact that I also want my line screens to be the same on all, and I know I am only using the 230 as my base. Top colors are 300 mesh.300 mesh, divided by 4 = 75 line screen.
300 mesh, divided by 4.5 = 66 line screen.
300 mesh, divided by 5 = 60 line screen
I would not use anything higher than a 60 line screen on a 300 mesh.Being that I want all of my art to be the same line screen between a 230 and up, I know I want to use a lpi that will work on my lowest mesh and higher.
So, I round off either lower or higher and I choose 55 lpi on a 230 mesh and use it for my 300's as well. All of this increases my chances of maintaining as much of the smaller dots as I can.
This applies to
S thread as well. The S thread does not jump you another 10 line screens but enables you to pick up another few more dots. You have to consider that you still have so many other variables that effect the dot quality as well such as "screen angle".
Once you know you're using the best choice of mesh (for the halftone used), you can still get moire from other variables such as the emulsion thickness, ink type, screen angles, etc.
22.5 is not (THE) correct one to use for (ALL) shops. Because lets say, your shop is a little more unique are using very thick ink on medium mesh, (thats one contributing factor), than add using a screen mesh that has a very low EOM Emulsion Over Mesh ratio, such as 1:1 of a thin fast pass of emulsion on a medium mesh or the opposite of that would be 2:2 of a very slow pass of emulsion on a medium mesh. Each of these can add to your chances of taking away from or adding to creating mesh opening to dot size/angle interference. Each shop is different but in general 22.5 does work
for most.
