Quote Originally Posted by markbarendt View Post

First, I added 2 red lines meant only to compare the steepness of the shoulders. The upper line is steeper. The steeper line means better separation of tones, it really is that simple.
Thanks for persevering with me Mark. Unfortunately I don't see why the absolute value of the steepness of the curve in the highlight/shoulder section is the thing to compare. I say this because I will be scaling the ENTIRE curve up or down based on the paper grade I select. For the sake of discussion, consider this scaling process to be proportional across the entire curves by assuming that the paper's transfer function is linear (I know it isn't but just assume it is for this point). So imagine I scale the upper and lower TRI-X curves to a position mid-way between those two curves. The shoulder sections will NOT lie on top of each other, and there will still be less highlight separation in the scaled top curve. I can tell this by observing that the ratio of D2/D6 (=21.3) is less than D1/D7 (=10.9). If they would lie on top of each other those ratios would match. Ignore D3 and D4 as I extrapolated those parts of the curves.

Greater highlight compression with longer development times for overexposed images.jpg
As you mentioned I should be comparing the middle curve to one below it, but the effect is too small to observe with the limited data present in those curves. If there was more data in the curves showing shoulders for each dev time then it would be easy to compare two middle curves, but in lieu of that missing data it is not unreasonable to assume the effect we see at the longest dev time exists in the middle curves at their shoulders if sufficient over exposure occurs.

Quote Originally Posted by markbarendt View Post
Second, is the captain obvious moment. While the theory can be compared using the Tri-X curve, the real shape of the HP5 curve is different. Its shouldering characteristics are different.
As I noted above, Ilford have not included any should information in their HP5 characteristic curve so we cannot conclude anything only assume. Even if its shoulder characteristics were different, I would be surprised if the general shape didn't generally follow that shown with TRI-X.

Quote Originally Posted by markbarendt View Post
And the basic shape of the shoulder isn't absolute, it will change depending on your techniques. It can be manipulated. Below is a good article.

http://www.apug.org/forums/forum216/...-negative.html
Very informative thank you. At least I know not to reduce my agitation lest I further compress my highlights !

Time now to walk the dogs and get to bed.

regards
Peter