Film Density By Zone
So the next question then becomes, "Cool, "so you're telling me zone 3, and then 3.2, "how do I know that?" Other than the fact that I completely made this up. No. (laughs) We look at film zone by density. So, when Fred Archer and Ansel Adams developed the zone system in the 1940s, they went through and they measured a number of different components of the film. And what they decided was, when film gets developed the initial film base was about 0.1. So that's called film base plus fog. That's the base exposure. We take the film base plus fog. So we know what that is. And then we're gonna take that and subtract that from every other measurement, because that's uniform across the entire film. That film base plus fog, to measure it we looked at that, and we cut the negative with that little gap between the two images, or we had that tail at the front and the back that I chopped off. We would measure that through a densitometer. The densitometer would tell us "Oh, film base plus fog is 0.0...
6." So anything I measured after that I would just subtract 0.06 from, and then that gives me the actual value of the target. Now, zone one ... I'm on a four by five. You can see there's different densities based on the size of the film. Because there's more information on a larger format negative. We can change the relationship between the zones a little bit, and the calculation. What Fred and Ansel figured out was that a really good negative density range was about 1.2. So the difference between zone 1 and zone was about 1.2. 1.35 minus 0.1, 0.25. 1.3, minus 0.1, 0.2. So we ended up with that range. That was the dynamic range at that time. So that was on those films and those papers. This still holds relatively close today, because we haven't had significant advances in film, because film's basically the same as it was 40, 50 years ago. And the papers haven't significantly changed. We're still using ... They call 'em the same papers, the papers today have less silver than they had. So the range is even different. They reformulate, and do kind of like the tabular work on the papers. They try to do all the work to keep the paper the same, with less silver, 'cause it's more economical for them. But in general, the ranges stay the same. So when we get a piece of film back, and I measure it under the densitometer at 0.28, I know that that's zone 2. If I go to 0.35, I know that I'm in zone 3. If I go to 0.55, I know I'm in zone 4. 0.7 I'm at zone 5. That is universal as a measurement of silver density on the film. So if I pick Delta 3200 or T-MAX 3200 from Kodak, and I pick Adox 20, zone 3 is gonna measure 0.45. So from film to film to film, that's how I determine that. Now when we're doing film testing, and we're doing the zone system, and we're like, "Oh, you know what would be great? "Is how do I figure out what my "actual film speed is?" 'Cause I told you, just take your film, cut your film speed in half, overexpose it by a stop, to start to build that shadow density. Well if I know zone 3 is a 0.45, and I know my zone 1, and I make an exposure, I'm able to then look at, under the densitometer, or I scan it, and measure it, do the logarithmic calculation exchange of math demon-ness. I do that, and them I'm able to say, "Oh, if my zone 3, say, was 0.26, "I don't have enough density to be a zone 3." 0.26 is closer to zone 2, I need more exposure. So if my film was rated at 100, I would then cut it to 50, and I would measure again. And I would say, "Oh, now my zone 3 measures 0.4. "I'm at 50, I'm not quite to 0.45." So now I'm gonna go from 50, I'm gonna go to, say, 40 ISO. And I'm gonna work my way down, until I get my density right. So that's how I'm starting to figure out what my true film speed is. This number: time of the developer. So once I know this, and I get my density right here, I then measure a zone 7. And if my zone 7 is 1.2, I'm in the developer too long. If my time is 0.75, I'm not nearly in the developer enough. So that's the basics of how I make the decision of how long am I in the developer for. I'm trying to get a know zone to be that specific density. And it's measured universally across the film. So this is the real nerd way to figure this stuff out. At the end of the day, what I do is once I know what zone 3 looks like with fully rendered detail. And I kinda know where I get that, and I get that by printing. If I think I metered that wall, or that wall, or the floor, and I'm like, "Oh, if I metered the floor at 3, "and I metered the TV at 7, and I develop, "I should be able to make a straight print "and 3 and 7 should show with texture." If 3 doesn't show up with texture, I need more exposure. If the TV's blown out, I need less development time. If the TV looks muddy gray, I need more development time. So it's all about looking at those. So even without having a densitometer, that's why recording what was your 3, and what was your 7 is so important in understanding how to get the most out of the film.