F/Stop Timing

f/stop Timing A different approach to darkroom exposure by Ralph W. Lambrecht The amount of light reaching a photographic emul- sion must be controlled in order to ensure the right exposure. Exposing the film in the camera is typically done with a combination of lens aperture and shutter timing. The lens aperture, also called ‘f/stop’, controls the light intensity, and the shutter timing, also called ‘speed’, controls the duration of the exposure. The f/stop settings are designed to either half or double the light intensity. The shutter speed settings are designed to either half or double the exposure duration. This is accomplished by following a geometric series for both aperture and time. The ‘film exposure control’ table in fig.2 shows an example of typical settings used in modern cameras and lenses. Therefore, an f/stop adjustment in one direction can be offset by a shutter speed adjustment in the opposite direction. Ex- perienced photographers are very comfortable with this convenient method of film exposure control and refer to both, aperture and shutter settings, as f/stops or stops. In the darkroom, the need for exposure control re- mains. Splitting this responsibility between the enlarging lens aperture and the darkroom timer is a logical adaptation of the negative exposure control. However, the functional requirement for a darkroom timer is different from that of a camera shutter, since the typical timing durations are much longer. Negative exposure durations are normally very short, fractions of a second, where enlarging times vary from about 10 to 60 seconds. Long exposure times are best handled with a clock type device which func- tions as a ‘count down’. Some popular mechanical timers, matching this requirement, are available. More accurate electronic models, with additional features, are also on the market. Some professional enlargers go as far as featuring a shutter in the light path. This fig.1 This image of old and worn piping was taken in the Botanical Garden on Belle gives an increased accuracy, but is only required for Isle, just south of Detroit, Michigan USA. The final print exposure and the print short exposure times. manipulation were determined by the f/stop timing method. f/stop Timing 19 fig.2 The film exposure is controlled with seconds. The test strip is then analyzed and the proper arithmetic series 150 10252035304 the taking lens aperture and the a constant difference (here 5) exposure time is chosen. In our sample, a time of less shutter timing. Both sequences are than 20 seconds would be about right. The printer geometric series 124812 6346 geometric and not arithmetic in a constant ratio (here 2) may decide to try 18 seconds and later alter it to in- nature for good reason. The print crease the time to 19 seconds to give it a slightly darker exposure can be controlled in the film exposure control look. Now, a so-called ‘base’ time is established. This same way with the enlarger lens sequence may be repeated for different areas of inter- aperture 425 32261118548. 6 22. aperture and a darkroom timer. [f/stop] est, for example textured highlights and shadows. If they deviate from the base exposure, dodging and burn- time 5000 255 102 60351 8421 [1/s] ing may be required. All this is then followed by a 3 second edge-burn to ‘pull’ the viewer into the picture. print exposure control This is a reasonable approach to printing and I have used it myself for years, but it does not utilize some of aperture 425 32261118548. 6 22. [f/stop] the benefits of f/stop timing. In the traditional, arithmetic timing method, uniform time increments pro- time 124812 63468162 225 51 [s] duce unequal changes of exposure. As seen in fig.4, the difference between the first two steps is 1/2 stop, or 50%. However, the difference between the last two Traditional Timing steps is only 14%, or slightly more than a 1/6 stop. A typical traditional printing session is simplified in Therefore, traditional timing methods provide too the following example. The enlarging lens aperture is large of a difference in the light steps and too little of set to f/8 or f/11 to maximize image quality and allow a difference in the dark steps of a test strip. This makes for reasonable printing times. The printer estimates it difficult estimating an accurate base print exposure from experience that the printing time will be around time. Now, let’s try another method. 25 seconds for the chosen enlargement. Typically, a 5 to 7 step test strip, with 5-second intervals, is prepared Timing in Stops to evaluate the effect of different exposures times. A My involvement with f/stop printing started when I sample of such a test strip is shown in fig.4 and was met a fellow photographer and printer in the UK. He used to test exposures of 10, 15, 20, 25, 30, 35 and 40 convinced me to give it a try. It didn’t take long to fig.3a (left) An analog f/stop dial from 8 to 64 seconds in 1/3, 1/6 and 1/12-stop increments. You may copy the dial and 64 attach it to any analog timer. 8 f/stop Clock Dial © 2000-Jun-24 Ralph W. Lambrecht 16 32 fig.3b (far left) Here the f/stop dial was enlarged and temporarily taped to a ‘GraLab 300’. 20 Way Beyond Monochrome fig.4 (far left) Traditional test strip in 5-s increments. (arithmetic series) fig.5 (left) New test strip in 1/3-stop increments. (geometric series) 10s 15s 20s 25s 30s 35s 40s 8s 10.1s 12.7s 16s 20.2s 25.4s 32s realize the major benefits of this very logical technique. consuming for a practical darkroom session. Incre- After a small learning curve and the typical discom- ments down to 1/12 stop are used as a result of mul- fort with any unfamiliar technique, f/stop timing has tiple print reviews with customers, critics and fellow now become the standard in my darkroom. It pro- printers. For normal paper grades, between grade 2 vides me with a new feeling of printing control and and 3, enlarging time differences of a 1/3 stop (~20%) the capability of being able to predict repeatable re- are significant in tonal value, 1/6 stop (~10%) can easily sults. I will explain the benefits of f/stop timing in the be seen and differences of a 1/12 stop (~5%) are minute, chronological order of a typical printing session from but still clearly visible, if viewed next to each other. the test strip, through the exposure adjustment for a Smaller increments may be of use for paper grades 4 work print, to the fine tuning with dodging and burn- and 5, but I rarely have a need for it. The analog dial ing, but first some general notes. clearly shows how f/stop timing fractions increase with Perfectly equal timing is only possible with the printing time. Fixed increments of time have a larger f/stop timing sequence, and fig.3 provides an analog effect on short exposure times and a smaller effect on version that will help us to understand the effect. It is long exposure times. a continuation of the well-known camera shutter The numerical f/stop timing table in fig.6 is a more speed doublings from 8 up to 64 seconds, and it is convenient way to determine precise printing times subdivided first into 1/3 then 1/6 and finally 1/12 than the previous analog table. It also includes dodg- stop. I selected the ranges because times below 8 ing and burning times as small as 1/6-stop increments. seconds are difficult to control with an analog timer, It can be used with any darkroom timer, but a larger and times well above one minute, I find, are too time version may be required to see it clearly in the dark. I f/stop Timing 21 Dodging [f/stop] Base Burning [f/stop] select base enlarging times from the timing table and I -1 -5/6 -2/3 -1/2 -1/3 -61/6 Exp +1/ +1/3 +1/2 +2/3 +5/6 +1 record all deviations in stops, or fractions thereof, for test strips, work prints and all fine tuning of the final -4.0 -3.5 -3.0 -2.3 -1.7 -0.9 8 1.0 2.1 3.3 4.7 6.3 8.0 print, including dodging and burning operations. -4.2 -3.7 -3.1 -2.5 -1.7 -0.9 8.5 1.0 2.2 3.5 5.0 6.6 8.5 Now, let’s get started. -4.5 -3.9 -3.3 -2.6 -1.9 -1.0 9.0 1.1 2.3 3.7 5.3 7.0 9.0 -4.8 -4.2 -3.5 -2.8 -2.0 -1.0 9.5 1.2 2.5 3.9 5.6 7.4 9.5 1. The Test Strip -5.0 -4.4 -3.7 -3.0 -2.1 -1.1 10.1 1.2 2.6 4.2 5.9 7.9 10.1 Assuming a typical printing session, I select the fol- -5.3 -4.7 -4.0 -3.1 -2.2 -1.2 10.7 1.3 2.8 4.4 6.3 8.3 10.7 lowing timing steps in 1/3-stop increments from the timing table: 8, 10.1, 12.7, 16, 20.2, 25.4 and 32 sec- -5.7 -5.0 -4.2 -3.3 -2.3 -1.2 11.3 1.4 2.9 4.7 6.6 8.8 11.3 onds.

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