Digital BW, The Print

> I made some graphs yesterday and interestingly (to me anyway), when
> the slider is at -6 for Dmax of 1.65(ish) this makes the luminance
> values more or less a straight line. When the DMax is 2.3(ish) the
> luminance is a linear straight line when the slider is at -10.



That pretty much jives with my experience as well. Were these Lab graphs?



> 
> In the end, as long as you're close and consistenet I guess it's still
> a 'salt to taste' issue.


Yes, but if you follow ICC standards
of workflow and proofing, you would want these scales to be
consistent with those standards as well - and that's a bit trickier.




> Hmm.. I've been calibrating to a gamma of 2.2 and using a 2.2 working
> space.  If it is closer to a gamma of 1.8 maybe it's worth the effort
> to change for future images.


Do you mean you switch the gamma at OPM to 2.2 as well?
Try it and see what works best. Currently I don't think OPM reads
embedded profiles. Take a 2.2 image and print it both ways:
with OPM set to 1.8 and then again set to 2.2. Also try the
same with a 1.8 image. It should be that you get a match
when the image gamma matches the OPM setting.

You shouldn't need to change anything in your workflow. If you
are set on 2.2 in your Photoshop environment, all you have to
do is remember to set OPM to 2.2 (it always defaults to 1.8 on
launch).  
For myself, I find that any setting that doesn't stay
on relaunch is one more thing to forget when printing -
so I try to save a "Job" if at all possible.



Antonis