On my way to photographic nirvana - a place of all knowing - I've hit my toe on a rock...
Please refer to the attached pdf's that are a printout from the BTZS program of a film in a developer. The film and developer are unimportant.
OK. Here goes...
In the family of curves, the low curve is for when the SBR is 9.8. The calculated development time is 4 mins, the calculated ISO is 50, the average gradient is 0.34 (I think). The printing of the curves has not shown what is in the program in that the densest sample in the table of results for the 4 min dev is 0.88. The printout is showing a solid line beyond this and the program shows a dotted line.
Where is the data on this curve? Where are the 9.8 stops? Are they between say the 2.1 and say 0.2 on the horizontal axis? Or would the 9.8 stops be from say the 2.1 to somewhere up in the 'dotted' section?
As I've learnt that not only do we want a gradient to match a paper we also want the data to fall in a specific range and to top out at a particular density. Perhaps the 9.8 stops tops out on the dotted line at a predetermined density of say 1.35??
This will then lead to my final question of ... OK so I measure a scene, I get an SBR. I refer to the data for my film and developer. The data tells me to shoot at a particular ISO and develop for a particular time. BUT! When I shoot 'normally' I would place my shadows at say Zone 3 or 2 stops lower than mid. If I have an extended SBR scene of the 9.8 stops for example and follow everything the curves and data tell me do I still place my shadows at the same point or do I move the shadow point to match the shift in ISO? ie move the shadows up the curve away from the toe by placing them at say 'Zone 4' instead?
I hope this makes some sense!
Rgds,
Steve
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