Subject: Re: raw 3.1 professional custom profiles for highend digital cameras
I have done many DlogH curves, and at one point, owned the Zakia /Todd book. No, the toe does not change much with increased development, but it does change. And yes the changes beyond middle gray (Zone 5; 18% gray)are greater than below, but again, it does change. Film speed does change as a function of development, and film speed is based (variously over the years) on just how the film comes out of the toe, it is inescapable that the curves pivot about the toe, roughly speaking, that is. The curves not only pivot there, the toe can increase in F+F value thereby showing a vertical displacement on the plot. If you take individual plots of a particular film over differing development changes, and overlay the curves such that the toes merge (roughly!), you will see that the slope of the curve does rise from the toe. I have lots of graphs in storage if you would like to see them.
I am familiar with AA's procedures. I studied and used them from about 1961. One of the reasons I ran so many curves is that I was interested in the so called compensating development, such as water bath, special formulas etc. I ran the curves on Plus-X, Tri-X, Tri-X professional, Panatomic-X, and other emulsions whose names I have forgotten. What I found out is that Plus-X didn't respond to compensating development at all. I could lay the reference curve over the DUT and they would match exactly. Quite a shock. I remember a film rated at ASA 250 that responded admirably, but way too grainy, even in 4x5.
I used two methods. One was to contact print a step tablet, the other was to shoot the tablet using an old diffusion head as a light source. I could tell how much support in the shadows I was getting from flare that way. Oh, and the one way that always worked was pre-exposure, sometimes post exposure. I could lift the toe nicely that way.
Plus-X had the straightest middle section of all. Ruler straight. Tri-X had a significantly different toe than Tri-X Professional.
Every meter measures luminance and can allow you to measure the scene dynamic range. A one percent spotmeter becomes an averaging meter for extreme telephotos, just as there is no such thing as a panoramic camera with a fixed lens. It's just cropping for the panorama, and whether a handheld meter is averaging or spot depends on the relative focal length of the taking lens.
The idea that a hand held averaging meter cannot give you the dynamic range of a scene is nonsense. Have you ever read "The Negative", first edition of AA? He explains how to use a meter to obtain dynamic range, if you cannot do that, you cannot even begin to use the zone system. He even described using a tube set into the meter element to do a rudimentary spot meter. I had several Weston Masters which had this homemade accessory. it was pretty neat, but boy, did it rob you of sensitivity!
Look, a metering system is simply some sort of light sensitive material which provides a change in some electrical parameter for a corresponding change in the light level. On it's own, you would simply see a needle move across the face plate. Putting numbers on the face plate corresponding to some light unit (Lux, Ft. Candles, Candles/ft^2, etc) allows you to quantify the responses. What you ultimately do with these numbers is one of the biggest parts of sensitometry as applied to photography. As you say, that application to digital is different than to film, but only because the demands of the digital medium requires it. I could just as easily build an exposure system for film based specifically on highlight placement. Film chose a different route, and, so far as I can tell, the optimum route. If digital and film had developed concurrently, perhaps we would reconcile the two systems so as to avoid the condition we find ourselves, at least those of us raised on film. The new guys, well, they will probably ch
ortle over the Dodge/Burn application. They will have no appreciation for negatives. It took a while in the darkroom with the counterintuitive nature of dodge/burn when I started up.
I am enjoying this exchange, Jeff. It clears the air, and reminds me that in order to most easily grasp the digital concepts, I am better off with my engineering hat than the photographer's hat. I'm in my late 60's and it's too easy to slip into old patterns. Changing hats works well, and I am glad I can do it.
Cheers, and goodnight! (my,oh my! It's 1:17AM here!)
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