Recently been having a problem with halftone banding, waves are appearing within the halftone patterns when exposed, onto the screen.
Image is 40lpi onto a 71t mesh (Something i've NEVER had a problem exposing before) EDIT: Halftone angle is 45 degrees, i know this is commonly known as a moire pattern, but it has never happened before.
Exposure time is 9mins 20secs through 8 actinic backlight bulbs in my Lumitron Odyssey vacuum lightbox.
The ONLY thing i have changed recently is my film brand, i have upgraded to an A2 roll from a different brand as sticking 2 pieces of A3 just wasn't cutting it anymore.
Could it possibly be the film brand? it's fantastic usually, 0 issues with it, ink dries faster, and is more opaque etc. The only reason i think its the film brand is that is the only recently changed variable and every halftone screen i have made with this film has these 'waves' within the halftones.
Another thing i thought it might be was my mesh tension? but again, never been a problem with halftones before.
Or possibly one of the 8 bulbs is under-performing therefore the light is undercutting the film, but they all turn on and operate fine as far as i can see.
This is the film over a white piece of paper:
This the film over my light box:
Both have no banding within the halftones, flush photo.
This is the test print:
As you can see, there are waves of halftone variation that shouldn't be there.
Try a different angle. 22 works best for us with one color prints. Develop your screen more carefully as well. Use a soft soft scrub pad(white color is softest I think) and scrub the screen on both sides while developing. It is common that a screen doesn't actually have a moire but that the littlest dots don't develop properly.
I rinse my screens with a light hose, don't scrub em! But i was wondering if it was dots not exposing, but it turned out everything had exposed (can tell usually due to slightly less opaque halftones that have't quite opened up)
It used to work fine with my old film, at any angle at all, i guess this new film (which is much thicker and has a slightly blue hue) must be playing with my halftones, it exposed well at 57 degrees, i'm just dreading the CMYK print i have to do this weekend on the new film, my halftone angles for that are; Yellow 5, Magenta 20, Cyan 80, Black 50
... so i might just add the same number to each value to make the degrees less 'uniform'