Determining exposure times with 2 different exposure calculators, or not

[Rockers]

We ran some exposure time tests yesterday with 2 different exposure calculators  on the same screen.
One was from Chromaline the other was the Saati 21 step exposure sensitivity guide. The out come could have not been and more confusing. While the Chromaline calculator indicated that we should be able to reduce the exposure time by 75% the Saati guide left us to believe that we do not need to adjust the time the screen was exposed at all. Now that`s confusing

[jvanick]

We ran some exposure time tests yesterday with 2 different exposure calculators  on the same screen.
One was from Chromaline the other was the Saati 21 step exposure sensitivity guide. The out come could have not been and more confusing. While the Chromaline calculator indicated that we should be able to reduce the exposure time by 75% the Saati guide left us to believe that we do not need to adjust the time the screen was exposed at all. Now that`s confusing

this goes right back to my post regarding how do you check for full cure of emulsion.

exposure calculators are only a 'guide' and not the end-all, be-all.

[Rockers]

I get that, but in this case there would be a difference of almost 45 sec in exposure time depending which calculator you prefer to trust.

[jvanick]

I get that, but in this case there would be a difference of almost 45 sec in exposure time depending which calculator you prefer to trust.

this can certainly be true as 'exposing for detail' can cause under-cured screens based on your light source and if it's under cutting or not.

suggestion would be to try AlBuffington's trick of wiping the inside of the screen on each of those right after rinse out with a clean white rag and seeing if you get any transfer of the emulsion color... (still not a 100% guarantee, but would certainly show you if it's grossly undercured)  -- I'm betting that a screen exposed with the time based on the chromaline test will be undercured.

you could also use a bit of screen opener on a rag on the screen after it's dried...

[GKitson]

I get that, but in this case there would be a difference of almost 45 sec in exposure time depending which calculator you prefer to trust.

this can certainly be true as 'exposing for detail' can cause under-cured screens based on your light source and if it's under cutting or not.

suggestion would be to try AlBuffington's trick of wiping the inside of the screen on each of those right after rinse out with a clean white rag and seeing if you get any transfer of the emulsion color... (still not a 100% guarantee, but would certainly show you if it's grossly undercured)  -- I'm betting that a screen exposed with the time based on the chromaline test will be undercured.

you could also use a bit of screen opener on a rag on the screen after it's dried...

Testing, 1,2, 3 and it is underexposed,  Try again please

[blue moon]

Keep going until there is no slime on the back, add a little bit and note what step you are on the Saati scale. Then leave the strip on the glass, and you'll be able to confirm your screens are getting the right amount of UV from there on. Make sure you cover the strip with a piece of film to accurately represent the light path.

Then go into your RIP and adjust the ink delivery and dot size to compensate for any undercutting.

Pierre

[Evo]

I do a step wedge test, WITH the Ulano calculator films.

On the same screen I do 2 or 3 different exposures of the Ulano film/ND filter combo (coarse film), at x1.5, x2 and x2.5 of the expected exposure units, then cross compare.