Speaking of Underexposure

[Frog]

I have one for you that constantly springs up. I have always learned that correct exposure time is correct exposure time regardless of bold shapes, fine detail, or halftone dots.
Could you address this?
Also, does the ability of photopolymer emulsions to benefit from re-exposure enter into this picture?

[alan802]

Yes Frog, I've always had issues with getting halftones to wash out when exposing fully.  We usually have to back off of the exposure time by a light unit or 2 with really fine halftones.  I'm sure our film density has a lot to do with this, our emulsion being PP and not dual cure, and maybe other factors I'm not aware of. 

[squeezee]

If you over-expose you will get more under-cutting, burn-through and light scatter.  These affect small elements disproportionately (because two are edge effects) which means halftones & fine lines.  Whatever you do you will get scatter from the film, from the mesh, from the exposure booth etc. 
So you expose enough to wash the  details out, then you can post-expose to fully cure the screen that's left.
From the emulsion's point of view, when it's exposed, it isn't going to get more exposed no matter how much light you give it.

[DouglasGrigar]

Yes Frog, I've always had issues with getting halftones to wash out when exposing fully.  We usually have to back off of the exposure time by a light unit or 2 with really fine halftones.  I'm sure our film density has a lot to do with this, our emulsion being PP and not dual cure, and maybe other factors I'm not aware of. 

Choosing a good match of dot to mesh helps, as does pressure washer, and art/positive adjustment when needed.

I would rather have a strong, fully exposed screen capable of long runs and quick easy reclaim than to underexpose.

Underexposure is the MAIN problem for new people in this industry, I find many of the suppliers promoting underexposure and it directly harms many of the new people in their early quest for efficient procedures an quality printing.

Have you noticed how many out there selling, hawking, and pushing products are ignorant of correct procedures, exposure, coating, positives, and art production? (Or lying for whatever reason?)

[Dottonedan]

Have you noticed how many out there selling, hawking, and pushing products are ignorant of correct procedures, exposure, coating, positives, and art production? (Or lying for whatever reason?)

Phfft.  Yea,  Thats why I dropped using one of he MAJOR suppliers in our area/actually nationwide I guess...and went with using Chris Colton and family. They were all intelligent and honest people. They knew what they were selling and also would tell you what was best after you've chosen to stick with the cheapest. They would lay the truth out for you and let you make the division.  Many just tell you what they sell and push that product....and they don't know for sure if it's good or they lie to you. They just push it because it's what the company is selling that they rep.  14 years ago, one company tried to push an oyo on us  (VERY hard) when it was clear we were looking for a true wet film image setter. It's just what they sold. They pushed so hard and lied to me that I decided not to use them at all for all of the other products that we were getting from them. We had to stick with them for some things and used them on emergency's of course, since they were in town.

[yorkie]

Underexposure is the MAIN problem for new people in this industry, I find many of the suppliers promoting underexposure and it directly harms many of the new people in their early quest for efficient procedures an quality printing.

New people don't understand the value of a quality exposure system, but think that an inexpensive system will do as well.  The same is true for a vacuum frame verses foam compression. And of course a timer is just as good as a light integrator.

Cheap units tend to have long exposure times, so it takes 10 minutes just to produce the underexposed screen with soft edges. Washout is inconsistent.

The need for especially dark film is a symptom of an out of control exposure process.

[DouglasGrigar]

Cheap units tend to have long exposure times, so it takes 10 minutes just to produce the underexposed screen with soft edges. Washout is inconsistent.

The need for especially dark film is a symptom of an out of control exposure process.

I don’t know if I would call it out of control, I can show someone how to control that - it is a situation that needs direct and specific attention.

A positive with low D-min and very high D-max is a good thing regardless of the power of the exposing unit...

We had to ban the use of amber masking film and then Ruby masking film because of burn-through with a very high power MH system (one of the big guys that would take a 5x8 foot screen and would dim the lights when punched) we had a high quality SA wet bath roll feed image-setter (24”x300’ roll feed) silver based system that had beautiful positives later and were using silver film from a camera before that and had the quality positives to make up for the ban on masking films... Amber was easy to see and crap to shoot... ruby ended up as a pale contender to silver films...

[yorkie]

Blasting through rubylith would be my definition of "overexposed".

[squeezee]

I spent years formulating masking films for Autotype.
Amber actually has the highest uv density OD 4 +, Ruby was slightly lower. 
I suspect that you weren't burning through the mask in the uv, an OD of 4 stops 99.99% of light at that wavelength, but that your bulb was putting out some visible wavelengths to which your screen was slightly sensitive.  The Amber lets more visible light through than the Ruby.

[RichardGreaves]

Douglas has a cool, interesting, one-of-a-kind story about a super powerful unknown lamp and a un-common, "high quality SA wet bath roll feed image-setter (24”x300’ roll feed) silver based system".  This would be in the "Formula One" stratosphere of equipment, especially on "theshirtboard".

In Wisconsin, I knew a guy with a rocket powered car. His gas mileage was poor.

For the rest of us here on earth, 4.0-4.2 UV density masking films work very well, especially in this age of 1.6 UV density 'stock' ink jet positives where many art departments don't want to bother with increased UV density they can get from a US$500 RIP.

I've personally made more screens in the sign or flag business with masking film than most people have had hot dinners and I was the Ulano product manager that lead the program to kill AmberLITH because of poor sales. I was very sorry to see it go.

"Cheap" is usually mixed up with "Low energy".  I would phrase an opacity statement differently than 'yorkie'. I encourage desire for controls, that's why I like to measure.  More UV density is more control. I'm a silver film lover from the 1970's.

[yorkie]

Your using silver based  film?

[RichardGreaves]

Since I am needling my friend Douglas about his professional 'old school' 24" silver film image setter, I went on record that I miss photographic films for screen making. 

"I'm a silver film lover from the 1970's", but alas most film use stopped at the turn of the century as film companies stopped making it and EPSON introduced the Photo Stylus 3000 for only US$1,100.  Much less than a wet darkroom or image setter.

[blue moon]

Since I am needling my friend Douglas about his professional 'old school' 24" silver film image setter, I went on record that I miss photographic films for screen making. 

"I'm a silver film lover from the 1970's", but alas most film use stopped at the turn of the century as film companies stopped making it and EPSON introduced the Photo Stylus 3000 for only US$1,100.  Much less than a wet darkroom or image setter.

There is a film house not to far away from here.  When I was starting they were producing some of my films. The Dmax and the resolution is just unbelievable!  It is pitch black, as in I have this piece of plywood and it is not letting any light through! And the halftone crispness was perfect. When you look at the halftone dots from an inkjet they are lumpy. Better ones look like potatoes and the cheaper ones look like blackbarries. Imagesetter film is perfectly round, no bumps nothing, just a circle (for a round dot). I've looked into getting one, but it is just not worth it. Customer will not see the difference so it is hard to justify the price. Still . . .

[DouglasGrigar]

Since I am needling my friend Douglas about his professional 'old school' 24" silver film image setter, I went on record that I miss photographic films for screen making. 

"I'm a silver film lover from the 1970's", but alas most film use stopped at the turn of the century as film companies stopped making it and EPSON introduced the Photo Stylus 3000 for only US$1,100.  Much less than a wet darkroom or image setter.

With the price of silver the use of the old silver based films is... well, do any of us know anyone who uses them?

Speed was an issue, silver imagesetters are (or were) very fast when up against an inkjet.

Amber always sucked, sorry guys, but it always sucked, I have a few samples left over and throw them on the unit every once and a while to show someone how they suck even up against an inkjet (with the special film).

Do any of us actually want to weed film cut with an x-acto again? I have better things to do at 3 in the morning.

[yorkie]

My memories of silver film is a bit more tarnished. I got involved with prepress with the introduction of a linotronic 300 running postscript level 1 on a 10 mhz rip. At that time, the linotronic was considered one large step backwards in quality. pre-press was accustomed to 4.0 film density, but the first generation of helium-neon film was lucky to get 3.1 on a good day. Put a newspaper on a light table and put lino film on top of it and the newspaper could clearly be read through the film. It was a LONG uphill battle to prove that lino film was usable.

Inkjet film is an entirely different animal. With silver, all of the silver starts off on the film, then the laser determines where the silver should be removed. With inkjet, the film starts clear and ink is piled on top of it. In the case of inkjet film, there is such a thing as "too much ink".

The Middle Way is the path between the extremes of self-indulgence and self-denial.