How To Read Printing Plates With The 500 Series Spectrodensitometer
How To Read Printing Plates With The 500 Series SpectrodensitometerThe 5xx series densitometers inherited "Patch Smarts" from the earlier 4xx's. Like the 4xx's they can be a bit stubborn when you attempt to push them to the outer limits of dot analysis. For example they fight over the color of paper or the value of a solid - - with newsprint or colored substrates for example. With the second release of the 5xx's series firmware we have relief! ;-) "Patch Smarts" can be disabled! With this feature in the off state the operator has total control of the instrument's data engine and funny papers, plates, even negative plates all become possible. You will need firmware version v9128 or higher to attempt this! The new 5xx's can also dynamically compute Yule/Neilson's "N" factor (if you can provide a good 50% dot).Proceed as follows: [ Part 1 - Disabling "Patch Smarts"]- Boot your 5xx.
- Press the Up key twice to access the "Configuration Menu".
- Press the Enter key and then scroll Down to the end of the menu list.
- Hilight the "Patch Smarts" option and press Enter.
- Hilight the "Off" option and then press Enter.
- Press the Back key (pointing up and left) one time and then the Exit.
You can (and should) re-enable "Patch Smarts" for most tasks. The above listed steps can be followed to return the function to the "On" condition.
Plates can be tricky. Often there are two dominant colors - (1) that of the base material and (2) that of the emulsion. To achieve the best data it is critical that a single color channel be selected and locked. The next few items will enable you to select the best filter and then to force the densitometer into that mode of operation.
What filter to use: [ Part 2 - Setting manual filter control ]- Select the "Density" Function.
- In either "Density ALL" or "Density AUTO" mode, measure the darkest location in the plate emulsion (the darkest area to the eye). Note the filter that returns the LARGEST value (in AUTO mode this is displayed by itself). This is the channel we want to use for these printing plates.
- Use the Exit key to return to the "Main Menu" then select the "Dot" Function.
- Press the Up key one time to hilight the "Options" command.
- Press the Enter key.
- The "Color :" prompt should be hilighted; press the Enter key.
- Scroll Up or Down to select a filter manually. Next press the Enter key.
As with "Patch Smarts", you will probably want to restore the Auto-Filter mode for conventional measurement of press-sheets and proofs. The above steps are for special cases (i.e., plates for example) only.
Chances are reasonable that an "N" factor will be required. While not a perfect solution, the Yule/Neilson "N" factor does a pretty good job of enabling plate measurements with a conventional densitometer. The 5xx's can dynamically calculate this value if YOU can provide a good, square-up, 50% dot. If you wish to set "N" continue else skip to the last section of this doc.
Now for the "N" factor: [ Part 3 - Automagically setting the Yule/Neilson N ]- Again select the "Dot" Function and then the "Options" command.
- Scroll Down and hilight the "50% Cal... " prompt. Press the Enter key.
- When densitometer prompts "Paper" (i.e., Measure Paper). Locate the lightest, brightest, cleanest spot on the plate*.
- For "Solid" locate and measure the darkest possible region.
- Next read THE 50% screen tint.
- The densitometer will compute "N". Hilight the "Save n" option and press Enter.
- Press the Back ( \ ) key to return to the "Dot Area" main menu.
| * | Firmware version v9128 requires that the lightest tone be the 'paper' and the darkest tone the 'solid'. With negative plates this is confusing. This action will be remedied in a future release of instrument firmware. |
Now that an "N" is properly stored it becomes quite easy to measure most plate materials. This last section details the procedure. Note that from this point forward the densitometer will 'believe' any action that you take. You can call anything 'paper' and anything else 'solid'. The instrument will quite happily read both positive and negative materials! To get good numbers YOU must properly establish these end points.
Reading plates: [ Part 4 - On with the numbers]- The routine begins with "Paper" (i.e., Read paper). Locate and measure the ZERO percent tone on your plate material; with a negative plate this will be the darkest region.
- Next locate and measure the "Solid" or 100% region. With negative acting materials this will be the lightest region.
- That's it... measure screen values till your heart's content. ;-)
Caveats, gotcha's, and such...
Yule-Neilson calculations (the "N"-Factors) have been used for nearly 40 years to 'adjust' the output of conventional densitometers. These adjustments are not perfect! Simply tweaking the "N" does not a plate reader make. However, with many materials this compensation is pretty darn good! Absolute microscopic accuracy is typically not really required of a good reading device. Rather the ability to repeat and reproduce a measurement is FAR more important.If you've dragged yourself all the way through this paper, congratulations! Your next step is to ensure that the densitometer can reproduce! If it cannot then it should not be used with these materials. An easy test is to carefully place the insturment on one region (I've even been known to use ScotchTape to prevent movement). Read and re-read this area 10 to 20 times. Convince yourself that the unit 'sees' with repeatable precision. You may also wish to turn the unit about the target - - if there is significant change in measured value the 5xx is out as a measuring device.