>Peter - Congrats! I am a mere mortal and don't get all this N-x talk, though, I do know AA's texts contain the whole explanation, however, in an effort to make this thread something mortals can follow, would you mind "101'ing" it? Like real brief,

Zsas, while the negs look printable, it wont be until I actually print them that I will know for sure if I am subjectively happy. Objectively speaking unfortunately I am not able to offer a lot of advice for others to follow unless I perform some more testing to determine the exact location of the curve's shoulder - and even if I did that my results/advice would only apply to people also using a similar combination of film + developer + target gamma. So in summary Zsas, in non Zone System speak, in response to over exposing my film by 4 stops I reduced my normal development time by about 10% in order to ensure my white puffy clouds would retain their detail.

**** DISLAIMER - I have not (yet) proven this dev time reduction was necessary ****

>Forgive me for being devilís 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.

Cliveh, the whole point of my post was to ensure success for a roll that I accidentally over exposed by 4 stops. OF COURSE I will also concentrate on not doing that again. That is a given. For the record here is how it happened. My hand held light meter (as would every other non ZS/modified light meter) gives readings to place the object I meter at Zone V whereas I wanted to place it at Zone III. That is a two stop difference. Instead of giving 2 stops LESS exposure than what the meter read, I gave 2 stops MORE exposure. I opened my aperture up two stops instead of closing it down two stops. I won't be making that mistake again in a hurry.

>It may also be worth mentioning it is difficult to say how much "overexposure" was given. Based on what? And how did we meter the scene? Etc.

Michael, I have calibarated my Exposure and film development process according to the "Elaborate and Precise" method described on p.217 of WBM 2e. I think it closely matches the methods described by AA in The Negative. Also Michael, below I address your comment about 2.1 probably not being where the shoulder lies.

For those interested in my observations/results so far here are some more details:

I actually had two rolls of film which I overexposed by four stops. The first roll of film (which up until now I haven't mentioned) I exposed and developed to N-1, and after inspecting the negs I realised my over-exposure error which prompted me to start this topic. A few of you suggested I run a test roll, well I decided that was a sufficient test roll as I made good notes of the meter readings at many zones in the image on that roll along with my exposure details. So last night before developing my second roll I measured the density of some Zone IX regions in that first roll (white puffy clouds) to be about 1.85 which turned out to be very close to my theoretical calculation of D_zone_IX_end = 1.74, in fact the reason it was a tad higher was because I accidentally over developed that 1st roll for a 7% longer period. So my theory was matching my practice. This then told me that I would indeed come close to 2.1 if I developed the 2nd roll as intended to N. As a quick aside, Michael suggested the value of 2.1 might not actually be the point my curve shoulders at owing to a different contrast index and developer etc (the HP5 datasheet shows a CI of 0.65 using ID-11), and he is correct, but it was what I used and only my own testing will ascertain the exact shoulder for my process.
So while my presumption about the shoulder point is not water tight, it served as a guide to me to want to slightly reduce my dev time to lower the gamma of my curve to possibly avoid the should should I have otherwise run into it. Until I do further testing to exactly locate the shoulder and how it responds to reduced dev time, I won't actually know if my method had merit or not.
So as I mentioned I proceeded to develop the 2nd roll to N-0.5 and this morning I measured a Zone VIII point on it to have a density of 1.74. this matches very close to my theoretical calc of where it should fall if I target a gamma of 0.45 (=N-0.5 in my process)
0.45=(D_zone_VIII_mid - 0.3)/((4+6.5)x0.3)
D_zone_VIII_mid = 1.72