Film

[Sbrem]

No the density of the ink. Dmin is how much light is blocked, ie the clear part of the film, and Dmax is how much light is let through, ie where the ink is.

I think you have that turned around, Mike, 'cause obviously clear film doesn't block much light. There is a tiny little percentage of light blocked by clear film (Dminimum) but not really enough to make a difference except on the most demanding situation, and the blacker the ink, the Dmaxier it is. Just want to keep Homer on the up and up.

Steve

[squeezee]

OD is logarithmic, so OD 1 stops 90% of the light, OD 2 99%, OD 3 99.9% etc.
So the difference between 2.5 and 3 isn't as important as you might think.
In addition, are you measuring in the visible or in the uv?  Some of you vets may remember Rubylith & Amberlith?  Good visible transparency but a uv density of about 4.  Just because you can see through the film doesn't mean that it isn't uv dense.  Ink manufacturers formulate their inks to avoid sunlight fading so they add uv blocks to their inks.
The difference between 2.5 & 3 will be seen in exposure latitude, a perfect mask means that you can expose for as long as you want, an imperfect mask will start to slow the wash out.

[ZooCity]

fixxon's  here too. 17" rolls

I want the crystal clear film back too.  The wp works "fine" but that clear stuff really shot some perfect stencils. 

[mk162]

I am measuring UV.

I also think that the WP film bleeds out more.  I have not had an issue with banding on my 3000 since I switched and we all know that is impossible to not have a single banding issue in almost 2 years.  Epsons are notorious for that.

[stitches4815]

Accufast 13x19.

[Northland]

OD is logarithmic, so OD 1 stops 90% of the light, OD 2 99%, OD 3 99.9% etc.
So the difference between 2.5 and 3 isn't as important as you might think.
In addition, are you measuring in the visible or in the uv?  Some of you vets may remember Rubylith & Amberlith?  Good visible transparency but a uv density of about 4.  Just because you can see through the film doesn't mean that it isn't uv dense.  Ink manufacturers formulate their inks to avoid sunlight fading so they add uv blocks to their inks.
The difference between 2.5 & 3 will be seen in exposure latitude, a perfect mask means that you can expose for as long as you want, an imperfect mask will start to slow the wash out.

That's good info squeezee....
So the difference between 2.5 and 3.0 D is about .45% of UV transmission ?
-- With the 2.5 blocking 99.45% of the UV and the 3.0 blocking 99.9% of the UV ?

[mk162]

That cannot be accurate.  Then if 3.0 is 99.9, then how can the measurement make it to 6 for imagesetter film?  Shouldn't like 3.1 or 3.2 be 100% blockage?

Do you have some documentation on that?  I am trying to learn all I can.

[Shanarchy]

Fixxons WP and am interested in seeing more talk on the dmin/dmax subject.

[Frog]

Brad I will see if I can get one of our local off setters to test our film, I know of one that has densometer but it is not portable.

Question is what is an ideal DMAX to shoot for? Has anyone published or discussed a good dmin dmax ratio?

This, from Ulano either answers your question, or offers an opinion, that can spur a debate. Notice that it doesn't give a specific d-min, but rather says that a good d.max is sufficient to overcome a less-than-perfectly clear film.

The “dark” and “clear” areas of artwork can be measured on a densitometer. The opacity of the dark areas is referred to as D-max (maximum density) followed by the numeric densitometer reading. D-min refers to the minimum density—which is a measure of the clarity of the artwork. D-max 4.0 is ideal for stencil making, as it allows full exposure of non-image areas even if the artwork medium is cloudy or fogged.

[mk162]

so according to Ulano, my measurements are bad

[inkman996]

What I would like to know what are the numbers based on, for instance obviously 0 is absolute dmin but what number is 100% light blocking?

[Frog]

Brad, maybe not bad as much as less than ideal.

Mike, according to Ulano, 4 is quite adequate for making stencils, even with the extra time needed with the frosty stuff. So, 4 must be getting close.

If you have the ability to measure, check out a coin. Ulano, in fact suggests a dime used as a control comparison when one has trouble washing the image out.


Here's the whole page on exposure.

[squeezee]

There is NO 100% measurement!  The act of measurement needs some light to be detected.  Honestly anything above OD 4 is trying to measure 0.01% of a light source.  The noise in the system is close to that.
The formula for calculating OD is OD=Log10(1/transmission) to convert from OD to transmission (TR) TR=1/(10^OD).
The difference between 2.5 (0.3%) and 3 (0.1%) is small and you would normally only see a slow washout.  IF the mask is even, you might be seeing unevenness in your positives (what we call holes).  Laser film is imaged with static electricity which repels particles of like charge, you tend to see dark edges and light insides.

btw I can bore for England on the subject 

[Homer]

There is NO 100% measurement!  The act of measurement needs some light to be detected.  Honestly anything above OD 4 is trying to measure 0.01% of a light source.  The noise in the system is close to that.
The formula for calculating OD is OD=Log10(1/transmission) to convert from OD to transmission (TR) TR=1/(10^OD).
The difference between 2.5 (0.3%) and 3 (0.1%) is small and you would normally only see a slow washout.  IF the mask is even, you might be seeing unevenness in your positives (what we call holes).  Laser film is imaged with static electricity which repels particles of like charge, you tend to see dark edges and light insides.

btw I can bore for England on the subject 

pfft. . is that all? wham bam boom, Bob's your uncle -you got yourself a screen. . . haha. . . .zooom. . .that was the plane going over my head.

[mk162]

No joke, that explains it well, especially if I would have understood it.