STE II

[DannyGruninger]

but you're still shooting through something that will block some UV light, or are those made to not block any UV

That's what I'm saying...... If I take a piece of clear film and lay over the printed ink from dts it slows it down minimum 30% but that number varies depending on mesh count.

I guess I'm just not understanding what Pierre is saying LOL...... I need to put the visual with it in order to understand LOL

[blue moon]

but you're still shooting through something that will block some UV light, or are those made to not block any UV

That's what I'm saying...... If I take a piece of clear film and lay over the printed ink from dts it slows it down minimum 30% but that number varies depending on mesh count.

I guess I'm just not understanding what Pierre is saying LOL...... I need to put the visual with it in order to understand LOL

film Dmin is not relevant here, the actual density of the step 7 is. So even though it's on the film, you should get the right readings.

pierre

[Orion]

The maker of our DTS supplies a digital file for exposure calculations. Maybe if one could get a really good scan of the 21 step calculator they could output it to screen...just a thought.

[Gilligan]

You sure Pierre?  Is that a straight nd piece?  Should I be putting that strip under a clear part of my film to compensate for the dmin of my film?

[jvanick]

You sure Pierre?  Is that a straight nd piece?  Should I be putting that strip under a clear part of my film to compensate for the dmin of my film?

I was taught to put the strip under my film .. I wonder if I've been doing it wrong all along?

[blue moon]

sorry not 100% sure of anything, but that is what I understand.
The film or no film, even on WP milky stuff, is so insignificant it should not make any difference. On a good film the difference is around 5% which is 6 seconds on a 2 min exposure. If you are within 5% of the full exposure time, you are better than 90% of the shops. We spent a significant amount of time and money on testing our screens and all said and done, we were underexposing by about 25%. The kicker is, our exposure times were 2-3 times LONGER than anybody else with similar emulsion and coating!!!

The moral of the story is, get the Stoffer strip and measure your exposure times!

pierre

[Gilligan]

Oh, I have one... it's TAPED to the exposure unit glass so it's NEVER left off of an exposure.

I just want to make sure we are using it right.

[ZooCity]

I'm not sure if this is 100% accurate but maybe to clarify:

The Stouffer 21 step greyscale strip is there to measure the quality/thoroughness of your exposure, not your resolution or imaging.

When calibrating for an emulsion we use a combo of the Stouffer strip as well as strips of test films- with halftones at various LPI as well as stochastic at common ppi and line segments at various points  -outputted from your regular device.

*CTS users may need to run the same screen through the unit multiple times, allowing to dry after each pass to get the various LPI outputs, etc.....presuming that is an option, or you may need to simply run through more screens.

To save screens on the calibration grid out the screen with a sharpie and, taking a best guess based off emulsion mfg tech sheets or experience, jot down a variety of LTU on each square.  Place the Stouffer along with the test films in one square at a time.  Cover the other squares with rubylith or anything that's 100% uv opaque.  Expose each square at the LTU written on it. 

Check your results.  Look for the correct hardness (step 7 intact) on the Stouffer and then, if there is a range of cells with the 7 intact, choose your optimal resolution.  Optimal resolution is going to be subjective based on what LPI or PPI stochastic or line point you commonly run on this mesh/emulsion/coating combination and what % range you need to hold in the case of LPI.  If you are long run discharge and waterbase all day long in your shop you may want to sacrifice the range for a somewhat over exposed stencil or even setup a spot color exposure value v. halftone/stochastic/fine line.
 
It's a bit of work compared to step wedges, winging it, etc. but it yields data that tells you what you can and cannot hold on a correctly exposed screen. 

Now, this business with the film is a little tricky because the Stouffer strip is obviously imaged film.  Your film may or may not be at the same dmin and dmax.  If you use CTS you have no film.  Pierre's suggestion to just put the strip on probably makes the most sense as the Stouffer strip, in my humble opinion, gives you a range of quality of your exposure, not an exact figure.  Resolving techniques are too varied (unless your using one of those sweet M&R washout systems) to expect to get perfect results and you'll find step 7 flapping around or sort of hanging on in some cases, rock solid in others.  You just want to be in that step 7 intact ballpark.  From there it's all about optimal resolution from your image setting device to the screen and, just as importantly, knowing what you can and cannot hold on various mesh counts/coats/emulsion types. 

[Gilligan]

Awesome input and technique Chris!

Only thing I have to add... Picking nits here... dMax isn't an issue with that strip because its an engineered neutral density filter... So it's opaqueness is based on X light passing through that step... Now YOUR dMax makes that step kind of relative as 7 being perfect is ok if your dMax is "good enough"... If it's passing light through it then you are exposing underneath your stencil to a degree.... Now you have a balancing act.

[ZooCity]

Great point! 

[bulldog]

I got this to start testing screens to get accurate times for my starlight (not DTS) since I really didn't have the slightest idea what to start at other than guess (way over) on my first couple screens.

http://www.kiwo.com/Product%20pages/Exposure%20films.html

The gist is you get 3 films, 1 for coarse screens, 1 for medium screens and 1 for fine screens. You put the film on the screen, then you cover it with a density sheet that is a lot like that 21 step test in that it covers each section on the film with a slightly darker segment.

You expose for double what you think it should be and then whatever section you can still hold detail on after washout is your factor.

For example, I tested a 110 screen at 15 seconds and was able to hold everything in the x0.5 column and up. 0.4, 0.3, etc washed out. So now I know on 110 screens that I coat the same as my test I only need to go 15 seconds x .5 or 7.5 seconds (I'll call it 8 seconds)

I'm attaching a couple images. Just quick cell phone captures...the one you can see where in the lower right box of 0.4 I started losing dots, I could hold them on 0.5

The other shows the film with the density film on top

[blue moon]

I got this to start testing screens to get accurate times for my starlight (not DTS) since I really didn't have the slightest idea what to start at other than guess (way over) on my first couple screens.

http://www.kiwo.com/Product%20pages/Exposure%20films.html

The gist is you get 3 films, 1 for coarse screens, 1 for medium screens and 1 for fine screens. You put the film on the screen, then you cover it with a density sheet that is a lot like that 21 step test in that it covers each section on the film with a slightly darker segment.

You expose for double what you think it should be and then whatever section you can still hold detail on after washout is your factor.

For example, I tested a 110 screen at 15 seconds and was able to hold everything in the x0.5 column and up. 0.4, 0.3, etc washed out. So now I know on 110 screens that I coat the same as my test I only need to go 15 seconds x .5 or 7.5 seconds (I'll call it 8 seconds)

I'm attaching a couple images. Just quick cell phone captures...the one you can see where in the lower right box of 0.4 I started losing dots, I could hold them on 0.5

The other shows the film with the density film on top

this is sort of what we did and were as a consequence using wrong exposure times for years. While similar, it does not have the step specified at which the exposure is correct (or so it seems as I read it). It looks like it is just finding the time that holds the best detail, rather than the time it takes to properly expose the screen. Or am I reading it wrong?

pierre

[bulldog]

this is sort of what we did and were as a consequence using wrong exposure times for years. While similar, it does not have the step specified at which the exposure is correct (or so it seems as I read it). It looks like it is just finding the time that holds the best detail, rather than the time it takes to properly expose the screen. Or am I reading it wrong?

pierre

You mean like the solid step 7 on the Stouffer strip? It does have that too, the part at the very bottom where the arrows are facing each other. In between the areas you look for your area that has no change. It's hard to tell because of the camera flash.

Brandon

[blue moon]

this is sort of what we did and were as a consequence using wrong exposure times for years. While similar, it does not have the step specified at which the exposure is correct (or so it seems as I read it). It looks like it is just finding the time that holds the best detail, rather than the time it takes to properly expose the screen. Or am I reading it wrong?

pierre

You mean like the solid step 7 on the Stouffer strip? It does have that too, the part at the very bottom where the arrows are facing each other. In between the areas you look for your area that has no change. It's hard to tell because of the camera flash.

Brandon

COOL! I missed that part. It makes a lot of sense and I'll probably pick one up as it just looks like a good tool to have.

They do point out the difference between the optimal exposure and optimal resolution: "It is possible that the optimum curing time and the optimum resolution exposure time differ slightly. For the final determination of the production exposure time, the requirements of the artwork should be the deciding factor, because: optimum curing = high resistance to long print runs, optimum resolution = finest detail quality."
This is a good point to bring up and gets me thinking about what we are doing. . .

pierre

[bulldog]

this is sort of what we did and were as a consequence using wrong exposure times for years. While similar, it does not have the step specified at which the exposure is correct (or so it seems as I read it). It looks like it is just finding the time that holds the best detail, rather than the time it takes to properly expose the screen. Or am I reading it wrong?

pierre

You mean like the solid step 7 on the Stouffer strip? It does have that too, the part at the very bottom where the arrows are facing each other. In between the areas you look for your area that has no change. It's hard to tell because of the camera flash.

Brandon

COOL! I missed that part. It makes a lot of sense and I'll probably pick one up as it just looks like a good tool to have.

They do point out the difference between the optimal exposure and optimal resolution: "It is possible that the optimum curing time and the optimum resolution exposure time differ slightly. For the final determination of the production exposure time, the requirements of the artwork should be the deciding factor, because: optimum curing = high resistance to long print runs, optimum resolution = finest detail quality."
This is a good point to bring up and gets me thinking about what we are doing. . .

pierre

Yeah, I noticed it is slightly different. I print for myself so I never do long runs. However, I think if I were going to I would probably go for detail and then post expose if needed.