Although each film has its own unique Lab Aim Density, the negative densities used for evaluation of these film stocks are the industry standards: Red .80, Green 1.20, Blue 1.60.

Methodology.

The methodology used is outlined in my published paper, "L.A.D. Testing Procedure, A Testing Method Developed by Mark Woods." Although this was originally published in International Photographer Magazine, May, 1996, I have recently updated it.

The Evaluation of the L.A.D. Plotted Characteristic Curves.

One needs to realize that the L.A.D. is the lab's optimum negative density for a given stock. It doesn't necessarily reflect the aesthetic choices a cinematographer makes when he determines the EI to expose the film. The L.A.D. is a point of departure for the cinematographer, a place to work from knowledge about a given stock. The "look" and quality associated with the density of the original negative, and "look" of the prints from that negative, will always be an artistic decision.

With that in mind, the Fuji 500 and the Kodak Vision 500T characteristic curves graphic representations provides insight to the films' imaging characteristics. For example, their printer lights:

Note that the printer lights are two printer points different on each light. The D-min and D-max are slightly different, and I might venture a guess that that indicates a slight difference in one stock's lower contrast. But both are high speed stocks with similar design limitations and performance requirements.

On examination of the characteristic curves, one can see the red and green emulsions track similarly, i.e., they have a matched sensitivity to "white" (3200 K) light. The major difference is in the blue emulsion. The Kodak Vision 500T's blue emulsion dips in sensitivity slightly at N+1/2 to D-min. The Fuji 500's blue emulsion begins to dip at N+2 and continues to N-2. What does this actually mean in the real world? The Kodak Vision 500T stock will reproduce color fairly true above N+1/2, while the shadows will shift very slightly toward yellow, or "warm" from that density to D-min. The Fuji 500 stock will do a similar rendition of color above N+2, but as the stop approaches N and dips lower, the tonalities will shift very slightly to yellow or warmer than the Vision 500T. The different angle on the graph indicates the blue emulsion's changing response to white light. This is not so different from some popular film stocks of the past.

I was curious if the film characteristics indicated on the charts would be reproduced on the screen. I can say that the shadows did shift to warm, although not objectionably warm. If one were shooting a period piece with lots of candles or kerosene lamps, the Fuji 500 might be a good solution. On the other hand, if one wanted a cooler shadow to represent dramatic points, then the Vision 500T would be the better choice. I feel a cinematographer might use both stocks in one project depending upon the scene's demands. This would be an artistic choice, much like mixing the paints on a palette. We already mix stocks, mostly for convenience, but occasionally for effect, this provides another option. In Out of Africa the cinematographer used Agfa on exteriors and Eastman Kodak 5248 for interiors.

Something equally interesting one can learn from examining the charts, is seeing graphically the film's response as the density shifts, particularly in the shadows. This is accomplished is by changing the EI of the film stock to achieve a more or less dense negative. I've often wondered why added exposure would make the blacks blacker when printed down. After viewing the characteristic curves and seeing the difference between N-5 and N-4, I could see that the density difference is greater in the shadows with added exposure. That difference is enough to perceive on a print, and on good telecine transfers. The darkest black is constant on both exposures, but the density difference is proportionately greater on the exposure with slightly more exposure.

Both films performed the way one would expect when exposed in this manner. When I shot the film test, after establishing the L.A.D., I exposed each film at the L.A.D., the recommended EI 500, and 2/3 of a stop more dense from the L.A.D., EI 250. Since I established the printer points for each film, the shift in density was compensated on the print by simply adding two printer points per 1/3 stop of added density.

By examining the charts for each EI, one can determine the approximate separation in the shadows and highlight separation. Cinematographers are continually concerned with the blacks being "black," and the highlights not blocking up. By determining the L.A.D. characteristic curves, a cinematographer can know with certainty where his shadows will have detail and where the highlights begin to block up. All of this is determined by reading with a spot meter the reflected light and the number of stops over and under N a given value is. The human eye is a wonderful artistic tool, while the spot meter is a field densitometer.

When I spot read the N-4 to N-6 values in the test scene, I was sure to make them large enough to be able to be read the negative with the lab's densitometer. I cross referenced the density readings from these areas with the density readings from wedge test I did to plot the characteristic curves. (A wedge test is simply exposing a gray card at the L.A.D., then six stops above and six stops below at one stop increments. It's critical not to use NDs on the lens, since the filter can subtly shift the color balance and give a false graphic rendition.)

The two densities, the wedge test gray card exposed above or below N, and the density in the scene exposed at the same value above or below N, were extremely close. If the spot meter is accurate, the densities will fall where the cinematographer expects. This doesn't take away from the artistic decisions he may make; it only quantifies their results. As artistic as the cinematographer is, he still needs to know the range of his tools. If he knows with certainty where a tonal value will fall, perhaps he may sleep easier at night.

On the charts with the films rated at EI 500, the density difference between N-4 and N-5 is not very great. While the density difference between N-4 and N-6 (approximately D-min), is also not very great in the red and green emulsions, while virtually non-existent on the blue emulsion (see chart of film stocks rated at EI 500). At EI 400, the density difference is slightly greater. This small added density is enough to perceive on the print since the print expands tonalities with its higher gamma (see chart of film stocks rated at EI 400). At EI 250, there is significant difference in the densities, in fact, the difference is so noticeable as to give a completely different rendering of the scene. This was true for both films. The difference between N-4 and N-6 was what you would expect in the more linear section of the characteristic curves. Since the exposure places these tonal values on the more linear section of the curve, they do have a more distinct and wider tonal separation (see chart of film stocks rated at EI 250).

As the density of the negative increased, the grain in the shadow areas decreased, and the N-6 areas (approaching D-min) were blacker. I didn't have the opportunity to read the print, but from my observations, the N-6 areas probably had more density in the print, consequently blacker blacks.

Summary

I feel the characteristic curves published by the two manufacturers are a good reference, but for critical work, one should shoot a "wedge" test, read the densities, and plot the curves. I know that in future L.A.D. tests, I will include a wedge test and plot the film stock's characteristic curves. Reading the data, unless one is very numerically inclined, is not very easy. While viewing a chart representing the data, it's much easier to perceive the characteristics of the film. Perhaps in the future the labs will provide the service to read densities, or the different offices of Local 600 may be able to provide access to densitometers for the directors of photography so they may better understand the current and new film stock's imaging dynamics. ¡

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