Gamma and Zone Systemgreenspun.com : LUSENET : Large format photography : One Thread
1. What gamma (approximately) corresponds to N, N-1 and N+1 development? How much would the gamma change for condensor head versus cold-light head?
2. Is "expose for the shadows and develop for the highlights" still true for modern films that have an almost straight curve?
-- Andreas Carl (firstname.lastname@example.org), August 07, 2000
#1- who cares? #2- you betcha!
-- james (email@example.com), August 07, 2000.
Some find security & creative freedom both in knowing just what point the testing tells them their negs should be at and at the same time produce creative and exciting images. Others are more free floating, developing & processing with little formal testing and still getting excellent results. If you find knowing 'the exact' helps, check with Fred Newman at the View Camera Store (darkroom innovations) and he can help a lot with this approach. He is good with it and promotes it. If you think the other approach will work for you, just go for it and refine on the fly. Either approach will work and can be adapted to your style of photography and your comfort level. If that is testing and precision in processing, etc., fine. If it is 'adequate exopsure & beefy negs', then go for it. Since changing the LF developing of negs to inspection I have been more comfortable in the darkroom as I can work somewhat 'on the fly' while looking at the negs as they come up in the developer & maneuver contrast & density a bit that way. It may be another crutch, but at least it works for me. So try whatever way you want knowing every excellent photographer from Weston to Adams to Sexton fine tunes their methods to suit themselves. The only 'one true way' lies in looking at excellent work in the form of the image, not how you got there. (even though that is a lot of the fun)
-- Dan Smith (firstname.lastname@example.org), August 08, 2000.
It's easy enough to work out the gamma, once you've decided what gamma "N" development is for your system, since gamma by definition is logDensity/logExposure.
Say it's 0.7 for example. This means that Density increases by 0.7D for every 10 fold increase in exposure. N+1 means that we get that 0.7D increase for a stop less exposure. For only a 5 fold increase.
We have to use logs at this point, but those modern thingies with LCDs and numbered buttons should take all the scare out of it.
Mine tells me that log 5 = 0.69897. Ah! Call it 0.7, it's only sensitometry after all, nothing serious.
So we divide our 0.7D density increase by log 5 (0.7), and (I don't need the electronic thingamajig for this one) the answer's 1. So N+1 development gives us a gamma of 1.
Likewise with the N-1 dev. Only this time the exposure needs to increase to 20 times to give us the same density. Log 20 = 1.30103. Divide 0.7 by ~1.3 = 0.53846. And that's our gamma at N-1.
Luckily, we don't ever need to calculate those logs again, they're constant for a halving or twofold increase in exposure.
To summarise, whatever the gamma is for N development, it's divded by 0.7 to give the gamma at N+1, and divided by 1.3 for N-1.
Now all you've got to do is look up the development times for those gamma values. Ba boom! (All donations gratefully accepted.)
-- Pete Andrews (email@example.com), August 08, 2000.
1. The average gradients for your question= .54 for N, .46 for N-1 and .67 for N+1. This is figured using the traditional zone placements as outlined in "The Negative". Some people figure using different zones and then these numbers would change. 2. Yes it still holds true. The negative materials have changed but printing paper characteristics are still the same. Sure it is possible to get a grade 00 now but would you really want to print on it?
-- Jeff White (firstname.lastname@example.org), August 08, 2000.