Plate Density...

kdw75

Well-known member
Can someone tell me where I might find the recommended image density for Sonora XP plates or Azura TE plates?
 

kdw75

Well-known member
I am trying to determine what the strength of a solid should be on the plates. I am using a plate densitometer to check the density and it is reading a maximum of .5 on a processed plate.
 

kdw75

Well-known member
I am trying to determine the correct amount of exposure. I am worried I might be under exposing the plates.
 

Alois Senefelder

Well-known member
Hello kdw,


Why are you making "Hard Work" for your self - - Just use a CtP plate exposure control strip such as - Fogra/Ugra !!!


Regards, Alois
 

kdw75

Well-known member
Why are you doing it by yourself? Your local kodak dealers do not have servicemen?
I had not considered asking them. Before we got our CTP we just used an exposure scale when we burned them from film. I figured there would be a similar method for a CTP system. I don't see why plate manufacturers wouldn't publish an exposure target for their plates.
 

kdw75

Well-known member
According to the device manual, you can print out targets and look for plugging of fine details, but this seems like an extremely crude method when you can simply measure the density using our plate densitometer.
 

kdw75

Well-known member
Is your "plate densitometer" capable for reading from processles plate?
No. You have to process them first. While it will read the density of the image, it wouldn't be able to read the plate background accurately unless you process it first.
 

cementary

Well-known member
No. You have to process them first. While it will read the density of the image, it wouldn't be able to read the plate background accurately unless you process it first.
So, you put them on the press, or clean with weak ipa solution and then measure "density" of imaged area?
Is it some kind of voodoo magic for setting up correct exposure?
are you sure you're using correct term "density"? 'Cause plate readers like Icplate from xriite do not measure density - those are just fancy microscopes with simple rgb camera. For correct exposure evaluation all you need is checkerboard patches and microscope
 
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kdw75

Well-known member
Well, that sounds like what I did. I printed tiny test patterns and they said to use a 20 power microscope to look for plugging of the patterns. The density meter tells me how intense the image is. If I up the exposure, it gives me a higher density reading. Just like on film and color bars.
 

gordo

Well-known member
Well, that sounds like what I did. I printed tiny test patterns and they said to use a 20 power microscope to look for plugging of the patterns. The density meter tells me how intense the image is. If I up the exposure, it gives me a higher density reading. Just like on film and color bars.
The problem is that the density reading is irrelevant. It's a thermal process. It's not like film at all. Using fountain solution on the Azura plate will work to remove the non-image area. But that's not how the Sonora works.
 

kdw75

Well-known member
The problem is that the density reading is irrelevant. It's a thermal process. It's not like film at all. Using fountain solution on the Azura plate will work to remove the non-image area. But that's not how the Sonora works.
Are you saying that it is binary? The image is either there or isn't?

How is the Sonora XP different? We have been using both and don't notice a difference.
 

gordo

Well-known member
Are you saying that it is binary? The image is either there or isn't?

How is the Sonora XP different? We have been using both and don't notice a difference.
Yes, thermal imaging is effectively binary. The coating is "cooked" by the laser during exposure. This is not the same process as exposing litho film and plate. When a plate is setup (calibrated) by the vendor engineer their job is primarily to have the ctp deliver a robust image on plate with no artifacts (like banding/stitching issues). The tone response on plate is not so important (as long as it's consistent). The tone response on the press sheet will be evaluated and if needed a tone compensation curve will be created to be applied in the RIP.

Basically, with the Sonora plate the fountain solution makes the unexposed coating sticky which allows the blanket to pull the unexposed coating off the plate and transfer it to the paper for removal. The first few (around 10) sheets going through the press clean the plate. With the Azura TE the exposure fuses the image area to the plate and the processor solution essentially washes the unexposed coating off.

Two different approaches to the problem. In marketing terms the Sonora plate is a true processless plate while the Azura would not be considered so since it has a processing step after plate exposure.
 

Slammer

Well-known member
Methinks you are asking the wrong question because you still have the film process in your mind. On the carton you will find a recommended energy in millijoule from the manufacturer, set this in your CTP and you should get the optimum exposure. Your dealer should also be able to supply you with this information.
 

kdw75

Well-known member
Yes, thermal imaging is effectively binary. The coating is "cooked" by the laser during exposure. This is not the same process as exposing litho film and plate. When a plate is setup (calibrated) by the vendor engineer their job is primarily to have the ctp deliver a robust image on plate with no artifacts (like banding/stitching issues). The tone response on plate is not so important (as long as it's consistent). The tone response on the press sheet will be evaluated and if needed a tone compensation curve will be created to be applied in the RIP.

Basically, with the Sonora plate the fountain solution makes the unexposed coating sticky which allows the blanket to pull the unexposed coating off the plate and transfer it to the paper for removal. The first few (around 10) sheets going through the press clean the plate. With the Azura TE the exposure fuses the image area to the plate and the processor solution essentially washes the unexposed coating off.

Two different approaches to the problem. In marketing terms the Sonora plate is a true processless plate while the Azura would not be considered so since it has a processing step after plate exposure.
Maybe that is part of the problem. Agfa advertises that you can go straight to press with the Azura TE without any processing, yet we seem to have trouble unless we use the washout gum. The Sonora works like a charm going straight on the press.

We are seeing the image working fine, but seeming to be fragile on the Azura. It currently looks purple, but if we up the exposure it turns more green.
 

kdw75

Well-known member
Methinks you are asking the wrong question because you still have the film process in your mind. On the carton you will find a recommended energy in millijoule from the manufacturer, set this in your CTP and you should get the optimum exposure. Your dealer should also be able to supply you with this information.
I will take a look for that.
 

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