following review appeared in the July/Aug 1999 issue of PHOTO Techniques
magazine and is reproduced with permission.
TRD 2 Densitometer
- by Phil Davis
Most large format photographers will agree that exposure meters are valuable tools for measuring light intensity or subject luminance, and most use them regularly. Similarly, densitometers are valuable for measuring negative and print densities for the purpose of process control - but very few photographers own them. Why?
There are at least three good reasons:
1. Lack of need. The vast majority or photographers aren't involved in darkroom work to any significant degree, so they have no use for densitometers.
2. Lack of information. Many photographers who might find densitometers helpful if they were aware of the potential benefits, donÕt understand what sensitometry can do for them, and aren't motivated to investigate.
3. Cost. Densitometers have always seemed outrageously expensive. The best argument in favor of densitometers is that they provide objective information about materials' characteristics and process behavior. Photographers who comprehend the significance of this information and bother to apply it, can save both time and supplies, and gain better control of the processes than is otherwise likely. In other words, densitometers are to photographers what tape measures and levels are to carpenters; certainly you can get along without them, but they make your work easier and more efficient.
Black-and-white densitometers are most useful to that relatively small subset of photographers who work in large format black-and-white and who are seriously interested in increasing their ability to predict and control the quality of their photographs. The connection is clear: image quality depends to a considerable degree on gradation; gradation is controlled to a large extent by the characteristics of film, film developer, and paper; and densitometers can analyze these characteristics with precision. "Knowledge is power," they say, and that certainly applies here. The information that densitometers can proved can unquestionably make you a better technician, and quite possibly - if you have the soul of an aesthete - a more confident artist as well.
A similar film test, analyzed in this case with a transmission densitometer, can provide reliable exposure and development data that you can use to produce negatives that closely ŌmatchĶ your chosen paper. Again, inspection of the film curves' contours can suggest their affect on print image gradation.
These relatively simple, economical test will show you that papers and films are not all alike; each has a "personality" that will influence the look of your prints. If you recognize the importance of these differences and study them, you can predict what their combined effects are likely to be. By revealing these materials' characteristics clearly and efficiently, densitometers can help you choose the combination of film, developer, and paper that is most likely to provide the image quality that you want.
These objective measurement techniques are equally applicable to such specialized darkroom procedures as making duplicate or enlarged negatives for non-silver printing. Platinum, kallitype, and photogravure are examples of historic processes that lend themselves to sensitometric analysis and control. In the cases of platinum/palladium and gravure, especially, the potential savings in expensive materials alone is a persuasive argument for sensitometry.
But despite this promise of materials' savings, it's been difficult in the past for non-professionals to justify the purchase of a densitometer because of the initial cost. It's unlikely that in any reasonable period of time, sensitometry can save enough in materials' expense to pay for a $3,500 instrument, even if your chosen materials are precious platinum salts or gravure copper.
To address this problem, simple black-and-white transmission densitometers have appeared on the market from time to time that cost less than $1,000. Of these, even the ones that are reliable enough to be useful solve only half the problem, because we need to be able to measure both negatives and print densities to establish reliable control procedures. Owning a transmission densitometer alone is like having only one shoe - it's certainly better than none, but definitely awkward.
Enter the Heiland
The TRD 2 is about 7 1/2 inches long, 4 1/2 inches wide, and 5 1/2 inches high, and weighs about two pounds. The hinged arm is about 5 1/2 inches long and has sufficient throat clearance to permit reading to the center of an 8 1/2 inch circle - enough to handle 8x10 negatives comfortably. The detachable power cord plugs into a socket on the back of the base, but there is no "off" switch - you have to pull the plug to power the unit down completely. A small slide switch on the right side of the base is used to select the operating modes - "R" for reflection and "T" for transmission. The "O" (the center position) is the standby setting that maintains power to keep the unit warmed up and the lamps disabled.
The specification sheet lists the transmission aperture as 2mm and, in this basic model, the aperture is not replaceable. Pressing the arm down on the film sample (against what seems to be unnecessarily strong spring pressure) turns on the reading light in the base. The density value is displayed in bright red numerals, to 2-decimal precision, in a prominent panel on the front of the arm. The performance specifications are conservative: the manual claims reading accuracy of +/- (1% + 0.02logD), which suggests that an actual density of 2.0, for example, might read as anything between 1.96 and 2.04. In my tests the accuracy was considerably better than that. Repeat accuracy is +/-0.01. The maximum rated transmission density is 3.5, but the instrument will actually read to 4.0 at 2% accuracy.
Converting the instrument to take reflection readings is just a matter of flipping the selector switch to "R". In that mode, lowering the arm turns on a lamp in the arm itself, and the light is beamed down onto the reading area at a 45 degree angle, a standard arrangement for reflection density readings. The maximum reflection density limit is said to be 2.5, which would be more than sufficient for reading any silver print density. As is the case with transmission readings, the readout is virtually instantaneous. In both operating modes, pressing a red button on the top surface of the arm will zero the instrument; the display flashes "-888" when the measurable reading limit is exceeded. This is a useful alert that's considerably better than simply providing a false value.
The Heiland designers have recognized that it is often very difficult to place a sample density area precisely in the reading area when the area is not illuminated, so they've arranged to switch on the appropriate lamp when the arm is depressed halfway. This makes it easy to identify the reading area visually, at least for reflection and medium density transmission samples, but positioning heavily dense transmission samples properly over the aperture is still a guessing game.
Although illuminating the reading area this way is generally helpful, there's a slight downside: you may be tempted to accept the density reading that is displayed as soon as the light is turned on. That would be premature, because the reading is not accurate until the arm is depressed fully. This is a relatively minor matter, but it is worth remembering that the armÕs return spring is strong, and that it takes firm pressure to get a correct reading.
The instructions recommend plugging the power cord in at least two minutes before you plan to use the instrument, and I found that the readings were stable after a short warm-up period. I did have to correct the zero adjustment occasionally at first, but it had never drifted by more than 0.01, and required no further attention after about the first half-hour of operation. I was surprised and pleased to find that after leaving the instrument on standby overnight, readings taken ten hours apart agreed exactly.
I was disturbed initially to discover that the TRD 2's transmission readings were consistently a little lower - and reflection readings a bit higher - than the values given by the two densitometers I own, despite the fact that all three instruments appeared to be calibrated accurately to their own calibration slips. The fact that they didn't agree with each other's calibrated test densities suggested that the companies may be using different calibration methods.
Pursuing this further, I tested all three densitometers with calibration strips supplied by several other manufacturers, and found variations that were not consistent enough to be conclusive. Finally, I checked the machines with a precision NIST (National Institute of Science and Technology) step tablet, and discovered that they were more or less straddling the precise density values - my densitometers were reading a little too high, and the Heiland, though closer, was a bit low. In fact, though, it was well within its published specifications, and when I used its exposure and development test data in a series of field tests, the resulting negatives were excellent. I have now calibrated my own machines to the NIST standard.
As a result of these findings, I consider the slight calibration differences mentioned above to be inconsequential. The lesson here is that densitometers frequently disagree to some extent, so, even though the differences are small, it's best not to combine readings from different instruments in a single test series.
The calibration strips supplied with the TRD 2 appear to be intended for information only, because there are no calibration controls for user adjustment. If the instrument needs calibration, it, along with its calibration strips, must be returned to the factory in Germany, or to an authorized service center here in the states, presently in Colorado. The densitometer is fully guaranteed from one year from the purchase date and will be repaired or replaced, free of charge, if it fails in that time period.
In short, the Heiland TRD 2 is a surprisingly capable and sophisticated instrument for its price, and, on the basis of its clean design, and its excellent performance in my tests, I can recommend it to any photographer who is seriously interested in using real sensitometric test and analysis methods to gain greater understanding of materials' capabilities, and greater control of the black-and-white process.
This article appeared in the July/Aug 1999 issue of Photo Techniques magazine and is reprinted with permission.
Phil Davis is a contributing editor for Photo Techniques magazine. A Photographer and writer he is the author of Beyond the Zone System (Focal Press), Photography (William C. Brown), and The Basic Photo Book (William C. Brown). Davis also teaches Beyond the Zone System Workshops at sites all over the U.S.
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