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HISTORY & OVERVIEW
This test grew out of a quest to discover a standard in film exposure, processing, printing, and telecine. I knew Eastman gave loops of film to telecine facilities to calibrate the machines. I was curious as to what standard Eastman used. I discovered the Lab Aim Density (L.A.D.). This is a series of densities for film negative, work print, and other stocks. The two L.A.D.s I was interested in were for negative and work print. These densities are based on the controlled exposures of negative film stock to 18% reflectance (neutral gray). The gray card is exposed at different Exposure Indexes (E.I.), and color temperatures, if necessary. The different exposures are read on a densitometer, and the one closest to the L.A.D. indicates the optimum E.I., and color temperature for the film. This L.A.D. negative is then printed on print stock with different printer lights until the L.A.D. is reached. The resulting printer lights to print an L.A.D. negative would be "normal" lights. Although this test indicates the L.A.D., that does not mean this is the only way to expose the film. All this test indicates is the optimum point of density for the lab to do it's best work. Cinematographers are artists who create unforgettable images by pushing the envelope of exposure and density, flashing, cross processing, and many other techniques. This test indicates ground zero for take off. CALIBRATE YOUR METERS Although this is pretty self explanatory, one could do the test and get consistent results with meters that aren't accurate. The only problem a cinematographer would have is if s/he were to use another meter calibrated accurately. The readings with the correctly calibrated meters would read inaccurately to the L.A.D. conducted with the miscalibrated meters. An interesting side point is, if the meters read consistently (off or otherwise) and the test is completed successfully, the results will remain constant with those meters, film camera, and camera. CALIBRATE YOUR GRAY CARD This may seem like overkill, but all gray cards are not equal. I use one that Mark Van Horn, from Foto-Kem, gave me. The reflected spot meter reading matches the incident meter reading. That is the true test of the meters. I have come across gray cards where the incident meter reading is off from the spot meter reading by as much as 2/3s of a stop. As you can see, this changes the E.I. of the film, and could lead to disastrous results. SHOOT THE TEST The L.A.D. film negative density of 18% (neutral gray) reflectance
is: The test is simply exposing the calibrated gray card at the recommended color temperature, and at the recommended E.I. of the film. In addition, make exposures one stop above, and one stop below the E.I. at 1/3 stop increments. Also, it is important not to have glares on the card, as this will affect density, and the resulting E.I. READ THE NEGATIVE DENSITY One of the exposures' density should be close to the L.A.D. The newer designed films tend to have a denser green layer. A few years ago, I could determine the speed of the film by looking at the green layer's density, if the red and blue densities were off. Now I have to look at balancing the red and blue densities and letting the green fall at whatever density it is-as long as it's not below the L.A.D. IF THE NEGATIVE DENSITIES DO NOT MATCH THE L.A.D. As I mentioned above, the newer designed films tend to have a denser green layer. That shouldn't be a worry to the cinematographer, as long as the green density is not less than the L.A.D. The more important densities are the red and blue density. If one is more dense, the other is probably less dense than the L.A.D. This is an indication of a bias in the film's color temperature. Depending upon which layer is more dense, the color temperature needs to be shifted in the opposite direction. EXAMPLE OF NON-MATCHING L.A.D. WHAT TO DO & WHAT E.I. TO USE A particular film stock is recommended to be exposed at E.I. 100 Tungsten (3200o K). After exposing the calibrated 18% gray card lighted with 3200o K lights and metered with a reflected light meter at the E.I., and in (stop increments above and below the E.I., the following densities were read off the negative at E.I. 160 (not the recommended E.I. 100): Red Green Blue The blue layer is slightly dense at 1.94 (.34 denser than 1.60). While the red layer is slightly thin at .74 (.06 thinner that .80). The green layer is close to the L.A.D. density of 1.20. To achieve the L.A.D., the cinematographer needs to add to the red layer which also decreases the blue layer. RE-EXPOSING THE 18% GRAY CARD AT DIFFERENT COLOR TEMPERATURES AND THE E.I. USED Since the green layer was close to the L.A.D. at E.I. 160, and
the red and green layer appear to have enough density to shift
the color temperature to reach the L.A.D., E.I. 160 is used for
the next step. DETERMINING THE COLOR TEMPERATURE BIAS OF THE FILM After processing, read the densities. In this example, at E.I. 160 and the color temperature at 2610o K, the film's density was: Red Green Blue Although the film is still off the L.A.D., two of the densities are fairly close. A further shift in the color temperature will only degrade the red layer without adding much to the blue layer's density. TELECINE AND THE L.A.D.-18% REFLECTANCE = 60% IRE What this means, is that the gray card is going to read 60% IRE on a wave form monitor. This is helpful in telecine when the cinematographer is not in a film to tape session, s/he asks the colorist if the skin tones are at 45% in a moody scene, or the key is hitting about 65% in a another scene. This is the type of control I like to have over my images. That is why I use a spot meter, and can predict how the image will translate to video. DETERMINING L.A.D. PRINTER LIGHTS For a workprint, the density for the L.A.D. is: Red Green Blue These densities are often shortened to "a hundred across,"
i.e., 1.00, 1.00, 1.00 in lab parlance. In our example, the exposure
on the negative closest to the L.A.D. is submitted. This step
will be repeated a number of times unless the lab is very good
and lucky. Most timers are very good, and will hit close to the
mark but not exactly. 1 PRINTER POINT = .0316 CHANGE IN DENSITY-6 PRINTER POINTS = 1 CAMERA STOP I wish it were that easy, but the printer lights are interactive with each other. A big change in one light affects the others, and the changes aren't totally linear. If one wanted to change .1896 (equal to one camera stop) the change may or may not be 6 printer points-especially in relation to the other lights. That's why one will probably have to submit the negative a number of times to attain the printer lights for the correct print L.A.D. The "normal" printer lights from our example film might be: 35 42 37 WHAT DO YOU DO WITH THIS INFORMATION? Once you have the E.I. of the film established, and the "normal"
printer lights established, shoot a scene, or do a lighting test.
When you turn the film in, call out the printer lights on the
camera report. When the lab prints the film without compensating
the cinematographer will see actual results of his or her work.
When shooting a film, with the printer lights called out, one
need not worry about the lab ruining an effect, or taking warmth
out or putting it in, or any number of problems we've all encountered.
The cinematographer is in control of the look of the dailies. In our film example that hit the L.A.D. at 2610o K, the cinematographer can get that "European" blue look by simply using this stock, 3200o K lights, and an uncorrected printer light. This test lets the cinematographer know the tools, the biases, and shortcomings of filmstock to better achieve desired images. IS THE L.A.D. FAIL SAFE? No. There are always going to be times the cinematographer will need the lab's help. In a perfect world, the cinematographer would print everything at one light-if that is his or her optimum artistic choice. Also, unless the film is processed the exact same way, and printed on the same printer there will be a slight variation from day to day. This is a fact of life in the lab. The labs do an excellent job in quality control, and most people can't see the difference in plus or minus one printer light. The printer lights are extremely close, probably closer than most cameramen can expose their film. DIFFERENT LABS HAVE DIFFERENT PRINTER LIGHTS, DO I HAVE TO DO THE TEST AT EACH LAB? You should do the test at each lab, but if a cinematographer took a negative of known density to a different lab, and had it timed, and read the printer densities until the printer lights reached the L.A.D., s/he could determine the printer lights for the film at that lab. This assumes that all labs process film negative to the same densities. Finally, this test should be viewed as a point of departure to evaluate film and determine printer lights. |