I guess that's a fair point, Gordo. If you were putting an imaging system through its paces what would you be looking for?
There are some ideas here:
Keep in mind that you're not testing the press - you're testing the plate imaging for consistency and image integrity. And as Alois noted - on press performance too.
Here are a few ideas for starters:
1 - Focus - does the CtP depend on the laser's depth of field to maintain focus? Or Hard focus where the laser is set up for focus on a specific plate? Or Auto focus where the laser is focussed and set each time a plate is imaged? Or Dynamic auto focus where the laser's focus point is continuously adjusted as plates are imaged?
Dynamic auto focus should give you more consistency in plate production.
A simple test is to take some masking tape and make a large "X" on one side of the back of the plate and then do the same, but with Scotch tape on the other side of the back of the plate. Image the entire plate with a screen of 30% then process the plate. If the "X"s show up as ghosts in the halftone screen then you'll seen how well the CtP copes - or not - with such small variations in plate thickness, debris on the CtP drum, coating thickness, variations in vacuum, etc.
Output the screened bitmap from the RIP and check, with your USB microscope, how well the halftone dots on the plate compare with the dots out of the RIP. They should be almost identical.
2 Focus/resolution. Create a series of tone patches of 1%, 2%, 3%, 4%, 5% and 99%, 98%, 97%, 96%, 95% and image at 240 lpi (for a 2400 dpi CtP). At 240 lpi with a conventional AM screen, the 1% dot is one laser spot - i.e. one pixel. Note if any of those tones is lost.
3 Thermal compensation/consistency. Have the vendor lower the heat in the room where their CtP device resides until it meets, or slightly exceeds the lowest temperature the device is qualified to run at and then expose two plates with the image of a grid taking up the whole area. Process one plate. Do not process the other. Now have the vendor crank up the heat in the room where their CtP device resides until it meets, or exceeds slightly the highest temperature the device is qualified to run at and image the unprocessed plate again and process. On this double exposed plate do you see one grid (ideal) or two overlapping? If overlapping, where and how do they mis register?
Wait a few weeks then reorder one of the above plates. Take the new plate and mount it on the press with the one that was previously exposed and processed. Can you register them? How is their fit?
You get the drift...
