This example shows HP5P 135 developed to a CI of 0.56 in Xtol. The graph on the left shows normal exposure with a resulting negative density range of 1.06. The graph on the right shows a three stop "over" exposure with a resulting negative density range of 1.02.
This example shows HP5P 135 developed to a CI of 0.56 in Xtol. The graph on the left shows normal exposure with a resulting negative density range of 1.06. The graph on the right shows a three stop "over" exposure with a resulting negative density range of 1.02.
View attachment 69433
Nice to see your program coming to the aid of a forum discussion!
PeterB, The reason our curves end abruptly on the right, is that "we" try to catch the toe in our tests and haven't done studies of gross overexposure... All it would take to see how far out the straight line extends... would be to remove a ND filter from the well of the sensitometer, pop a test, and develop and measure it. I believe there is a great long straight line ahead.
Thanks Bill. I'm curious as to why films are rated with so much latitude for over exposure but virtually none for under exposure ?
regards
Peter
The curves for TXP aren't showing it reaching D-max so, no to that part at least.
TMY can hold about 14 stops on the straight line IIRC, so if you had used TMY instead of HP5 for the shots that started this thread you could have exposed another three stops (7 stops up total) before you even got to the shoulder let alone finding D-max. So again no, the generalization doesn't work.
I wouldn't suggest that. Soft working developers and/or reduced agitation can make the film shoulder earlier. That's exactly what Peter doesn't want.
Edit: this is a response to post #23.
Whenever I have tested films/developers I have always tested including the shoulder region because it is important in my work. I've done this with several films and developers - over and over. There are quite a few variables to consider and both the shape of the shoulder and where it begins are subject to manipulation. The only rough generalization I would make is that the films I've tested tend to exhibit their longest straight lines when developed to an approximately normal CI. Underdevelopment tends to shorten the straight line due to increasing compression on both ends, and gross overdevelopment moves the shoulder to the left for obvious reasons. On the underdevelopment side, different developers and techniques can have some effect on the curve shape.
I would suggest you simply move on from your overexposure error.
Hi folks,
I was rather annoyed at myself to discover that I over exposed a 120 roll of HP5+ by a whopping 4 stops ! The good news is that I think my highlights will not be compressed at all but I wanted to run my solution past you.
The SBR was 7 stops from Zone II to VIII inclusive which would have otherwise lead to Normal (N) development time. In short I plan on reducing the film development time to be that for N-1 which in my process will lower the gamma from 0.5 to 0.4
Below you can see my analysis, but I am amazed that I can still keep my scene in the straight line portion of the curve by forcing a minor reduction to its CI/gamma/slope. I will just print using 1 grade harder MG filter. What am I going to lose out on here ? This seems too easy to recover from.
** warning that a bit more theory and maths will now follow... **
I have analysed the HD/characteristic curve of HP5+ and it is linear out to at least a density of 2.1 log units which has basically been my saving grace here. Normally a neg exposed for N development in my process would result in a density ranging between 0.3 and 1.35 on the neg. [gamma=(1.35-0.3)/(7x0.3)=0.5]. 1.35 is nowhere near 2.1 but 4 stops over exposing would put the density right on 2.1, however if I reduce the gamma to 0.4 and calculate the range for Zone II to IX, you will see it comfortably makes it in. I am calculating from zone II up to Zone IX (i.e. an 8 stop range) as I want to include even the last nuance of detail in my highlights. So here is the formula:
Gamma=0.4=(D_zone_IX_end - D_zone_II_start)/((4+8)x0.3)
0.4=(D_zone_IX_end - 0.3)/((4+8)x0.3)
D_zone_IX_end = 1.74.
Now because D_zone_IX_end<2.1 , I should be OK. In fact because I still have a bit of wiggle room I could develop to N-0.5 which would give D_zone_IX_end = 1.92 Developing for N would put D_zone_IX_end right at a density of 2.1 and permit no room for any error in dev time/temperature/age/minor film exposure variations etc.
regards
Peter
Forgive me for being devils advocate here, but if you are over exposing by 4 stops, isn't the rest of your post irrelevant, as you should concentrate on exposing correctly.
I sincerely hope the silliness of cliveh's posts is intentional.
Probably not, but perhaps I'm misreading the original post. Perhaps you can please explain.
Have you ever screwed up something important
Yes, but have tried not to repeat it.
I think Peter will endeavor not to repeat his mistake too and he learned things he didn't know and has new questions to answer.
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