I just drew a set of curves for an APUG'r and the lowest contrast negs have beautiful smooth toes that I know I could just reach right into to print a negative shot at half box speed. If I took the 0.1 density to base EI, it would say quarter box speed. But half box speed is more appropriate.
Originally Posted by DREW WILEY
This is one of the factors I believe leads to lower Zone System speed ratings. When you develop N-1 etc, you may not achieve full speed. Especially if you rely on 0.1 density as the point where you take your speed reference.
And when I know that more of the toe is usable, I am reluctant to use 0.1 density-based speed.
Just depends on what look you want. Minus development sacrifices midtone expansion and microtonality
to some degree. I'd rather have full development and use and accessory unsharp mask to bring the
highlights into control, provided the original neg holds all the relevant information. The whole Zone
System mentality tends to be taught on a generic basis. But even when Ansel put the last version of
this in print, there were radically different popular films available. Something like Pan-X was engineered
for high-key studio portrait and fashion work, with a very long sweeping toe, while Super-XX had a
deadpan straightline from the basement to the moon. Tri-X was somewhere inbetween. Then Minor
White basically made a nutty religious cult out of the whole concept. It really isn't all that complicated.
Ooops, made a typo. Meant to say, Plus X pan had a long toe. The nearest equivalent today would be Delta film.
Bill, as you know that is essentially the logic underlying 0.3G (which is analogous to the first excellent print). Actually Stephen's summary paper on Delta-X does a good job illustrating how when developing to different gradients you still end up with virtually the same speed (as opposed to a fixed density criterion such as ZS).
Originally Posted by Bill Burk
My own caveat (not part of the theory) is you might have to assume a relatively normal luminance range. But I am not really there yet. Have a lot more reading to do first.
Where does it say that? I made a post last night on the other thread on this topic.
Originally Posted by Michael R 1974
Drew, the various toe shapes is one reason why fixed density film speeds like the Zone System method are inferior speed methods.
It doesn't say that. That was my own "kind of" caveat. I'll edit that now.
I'm a little behind in the other thread so I haven't read your most recent post. Apologies.
Back to why Zone System and ISO "speeds" are different. With the Zone System, you meter a target and stop down four stops. In the example below, the ISO speed of the film is 125. That means the exposure at 0.10 over Fb+f is 0.0064 lxs making 0.8 / 0.0064 = 125. The metered exposure is 8 / 125 = 0.064. Four stops down from the metered exposure is the exposure 0.0041 or too low for the 0.10 density speed point. In order for the four stops down exposure to fall at 0.10 over Fb+f it requires 2/3 stop more exposure. One way to do this is to rate the 125 speed film at 80.
Yes, I am repeating myself, but hopefully in a slightly different way. So Bill, except for experimental error, for general purpose developers this is the primary reason why Zone System EIs and ISO speeds are different.
Well, now THAT is one heck of a good, simple explanation.
Originally Posted by Stephen Benskin
And it explains why an Incident Meter reading, won't agree with a Spot Meter reading, where the shadow is Placed on Zone (shadow Zone of your choice).
Would this mean if I translated the ISO speed point into a zone would it lie at zone 0 1/3 from the view point of the ZS?
Part of why I asked the question. I think the practical implication is that when you Place Shadows on Zone II, you fundamentally make the "2/3 stop" adjustment (even though you make a whole stop).