Got a problem that I can’t understand…

I have a DI press. When it was setup, we linearized it and then selected the dot gain curve we wanted. So basically we made sure 50% was 50%, then asked the rip to make 50% become 70% for example. All this was done at 150 lpi and we made profiles.

We want to move to 175 lpi so I linearized the press at 175 lpi and applied the same dot gain curve as we used for 150 lpi.

The natural dot gain of the press showed me that 175 gained more than 150 if I remember correctly. This told me that the same image printed at 175 would appear darker compared to 150.

My proofs were a pretty good match to the press at 150 lpi.

Now, when using the profiles I made at 150 lpi, with the press running at 175 lpi, my images appear lighter compared to the proof. I don’t understand this. I figured that since I’m asking for (and getting to my knowledge) the same dot gain at both line screens, the profile should still be ok. At worst, I expected the output to be a little darker but it appears to be lighter. (I’m running to the same densities)

My proofs are basically useless for 175 lpi now which is obviously a big problem.

Is my logic wrong? I don’t understand what’s going on so I have no idea how to fix this problem.

Any help is appreciated.

Thanks,

Mark