Comparing paper characteristic curves

[radiant]

So I think that was a bit of a rash conclusion, to be honest.

Sorry , still learning..

 

[koraks]

No worries, I'm not saying that you were wrong, just that I would personally not necessarily arrive at the same conclusion. As far as I'm concerned, we're only scratching the surface in this thread, and it makes me curious for more. So I'd consider it a pity if we tried to conclude something now and call it a day!

 

[radiant]

No worries, I'm not saying that you were wrong, just that I would personally not necessarily arrive at the same conclusion. As far as I'm concerned, we're only scratching the surface in this thread, and it makes me curious for more. So I'd consider it a pity if we tried to conclude something now and call it a day!

No - no that was not my point. I tried to conclude something that I maybe had learned so far. And failed on it. So lets not totally call it a day and keep going, as a learner this is like a gold mine for me

 

[bernard_L]

Insofar as any conclusions can be drawn, the curves for the foma papers seem somewhat more attractive to me at the higher grades,

Well, grade 5 does not have the "dual-slope" shape of that is most apparent in grade 2. But OTOH, grade 0 is linear in almost textbook fashion.

This said:

• As I already stated, If one looks closely at the curves in datasheets for MCC and Ilford, one sees there also this "knee" in the middle of the curve for intermediate grades (say, 2-3). Another thing would be to do actual measurements to replace the "artist impression" curves in the datasheets. I never had MCC paper, and any Ilford I have is too old for reliable measurements. Plus, actual prints are more gratifying than technical measurements (see next point)
• It remains to be proven that a linear D-logE curve for the paper is actually desirable. I've had (as already stated) nice results (as judged by other viewers) printing a series on Variant 111, generally at grades 2.5 or 3 in 30x40cm (12x16"). It's difficult (and maybe silly) to analyze an aesthetic impression in technical terms, but maybe:
  • the dual slope raises just a little the middle tones in a pleasant way
    
  • the higher slope in the dark tones helps compensate for the degraded perception of tone separation when a print is viewed in less than optimum lighting
  • and also the dual slope helps fit a larger range of high values in a way which is different (and better) than an extended, progressive print shoulder as produced, e.g. by sub-threshold paper pre-lashing, or by compensating development of the negative.

 

[koraks]

I agree with you 100% that a pretty curve does not necessarily make a pretty print. The question is more complex and likely dependent on the image and the intent of the maker. So this does force me to reflect more on all this from a perspective how I want my prints to turn out, and how to translate that to more technical decisions. Great, we're getting somewhere!

 

[radiant]

@bernard_L Can you plot the delta change in the Fomabrom 111 charts? For me it is really difficult to see those parts that break the linearity for example the dual-slope. Now I can see it of course that you pointed it out

 

[bernard_L]

So this does force me to reflect more on all this from a perspective how I want my prints to turn out, and how to translate that to more technical decisions.

The difficulty (and the beauty?) of the analog workflow is that (compared to hybrid or d*****l) there are only few controls, and they do not provide instant feedback ;

• negative dev time and/or choice of paper grade (to first order) define the subject brightness range that can be translated on paper; together with exposure time, this defines the analog of white and black points.
• to second order, we have some manipulations of the shape of the curve: compensating developer, choice of film (e.g. 320TX with its upswept long toe), selective highlight bleaching, Se toning, etc.

As for myself, I have more limited ambitions: see when a result is pleasing; sort out whether it is a result of the scene (light, etc) or a favorable film-dev-etc combination, and if the latter, try to reproduce it (of course I keep notes)

 

[bernard_L]

Can you plot the delta change in the Fomabrom 111 charts? For me it is really difficult to see those parts that break the linearity for example the dual-slope. Now I can see it of course that you pointed it out

I suppose you mean the derivative (slope). That is where I reap the benefit of having fitted the measurements with a spline: straightforward (leaving aside the details of programming) to compute the derivative/slope. So there you are. My curves are not as pretty as those of http://www.darkroomautomation.com/support/appnotevcworkings.pdf His curves are entirely made up in the computer, and according to the point he is trying to push ; moreover they are disconnected from reality; e.g. in the real world there is no plateau in the middle of the Grade 0 D-logE curve.

The little wiggles in the curves below are not significant. What do we have?

• Grade 0: constant slope (except of course slope drops to zero at both ends)
• Grade 5: slope peaking in the middle; i.e. an S-shaped curve (often introduced in d*****l processing to add "snap" to the midtones)
• In-between: slope generally rising from dark to light tones and peaking around D=1.5 (darkish gray) (always zero at ends, of course).

 

[radiant]

I suppose you mean the derivative (slope). That is where I reap the benefit of having fitted the measurements with a spline: straightforward (leaving aside the details of programming) to compute the derivative/slope. So there you are

Thank you so much, I guessed that it is easy for you to generate such graphs I really meant the difference (aka change) of the derivate but these graphs are already so good - the change is already visible / grade 1 & 2 bumps are now more visible. I wish all papers had such graphs too

If you still want to generate a derivate change graph, please plot all grades on same picture too

 

[bernard_L]

If you still want to generate a derivate change graph,

One can perform only so much processing of experimental data before it becomes meaningless. Even the derivative plots (my previous post) do not, IMO, show anything that was not already visible in the regular plots.