At the Paralympic Games in Atlanta in 1996, digital capture was on the horizon. It wasn’t ready for prime time. The photograph above is of the Canadian Tandem Cycling Team. The athlete on the right steers while her blind teammate adds power. They are multiple gold medal winners. I made their portrait on Kodak Tri-X film ISO: 400. This post is part of a series on photography’s basics on the three components of exposure: Shutter Speed, Aperture and ISO. Before a discussion of any of these three pillars of exposure happens, a question has to be answered.
What is an f/stop?
An f/stop also known as a stop is an amount of light. F/stops either double the amount of light (2x) or cut it in half (1/2x.) Each of the three components of exposure: Shutter Speed, Aperture and ISO are measured in stops. A stop of light is divided into thirds. Exposure can be increased or decreased in 1/3 of a stop steps in ISO, Aperture and Shutter Speed.
ISO controls the sensor’s light sensitivity
Simply put the higher the ISO the less light the sensor needs to render an image. Low ISO usually provides the best quality image. Higher ISO’s allow shooting in very low light. Higher ISO images typically have more noise in them. ISO is an acronym for International Standards Organization.
The ISO range of digital cameras today is quite wide even for prosumer models compared to film. In the latest professional cameras, it’s extreme. Nikon’s newly introduced D5 has a standard ISO up to 102400 expandable to 3276800. That’s three million, two hundred and seventy-six thousand two hundred. Nikon rounds it up to 32800000. Canon’s just announced D1x Mark II’s standard ISO is 51200 (1 stop less than the D5.) It tops out at 409600 (three stops less than the D5.)
Currently available ISO’s
Below in full stop increments is the available range of ISO’s in the Nikon D5 currently the ISO champ. The numbers at the left are the least sensitive to light. They are referred to as slow. Numbers to the right are more sensitive. These are fast speeds. The asterisks in between the full stops indicate one third and two thirds of a stop respectively.
The chart above lists a sixteen stop range. Each stop doubles sensitivity. By the time Nikon’s D5 gets to its highest ISO, the sensor requires 1/16384th the amount of light it does at ISO: 50. Very impressive. I look forward to seeing what photographs at the highest look like. The bottom line is that these extreme ISO values allow photographers to capture photographs that could not be made or made as well a mere five years ago.
ISO: grain & noise
Before digital, ISO (a.k.a. ASA or DIN) was determined by the film. Different films had different ISO’s. Ultra fine grained black and white film like Kodak’s Panatomic-X was rated at ISO: 32. Kodachrome 25 color slide film was also a very fine grain color slide or transparency film. The ISO was so important it was in the film’s name. Slow (or low as we describe them today) ISO’s meant high resolution and very tight grain. Grain is the size of the silver halide crystals mixed into gelatin that coated the film’s base. Faster, more sensitive films required larger crystals to work in lower light. The higher a film’s ISO the more grain clumps would show in the final print or slide. ISO 400 black and white films, Ilford’s HP5 and Kodak’s Tri-X were the staples of photojournalists, editorial and some fashion photographers. Color slide films topped out at around ISO 1000 thanks to Scotch (later Imation.) Black and white on the other hand went up to ISO 3200 for Kodak’s High Speed Recording Film used mainly in surveillance cameras and rarely in general photography. The price of this sensitivity was ultra large clumps of grain. The grain on the high speed films was breathtakingly huge. Some saw it as beautiful photographic pointillism. Others found it simply obnoxious. The lesson here is low ISO equals fine, tight grain. High ISO produces large grain structures easily seen in prints. Check out this handsome lad from half a century ago captured on Kodak Ektachrome color transparency film ISO: 16. A close look reveals the grain.
Night photography was a challenge too. ISO 320 with a color transparency film was the fastest available in the late ’80’s.
Noise artifacts in digital are constantly improving. In-camera noise reduction gets better with every new camera generation. Noise reduction in RAW processors like Adobe’s Camera Raw in Photoshop, Bridge and Lightroom’s Develop module, Canon’s Digital Photo Professional and Phase One’s Capture One have incredible noise reduction tools.
The subway slumbering man was photographed in as dark conditions as the swimming pool above. The grain it much tighter even though the ISO delivers three stops more light than the film did.
Below, the photographs are ISO: 6400 on the left and ISO: 12800 on the right. The top row shows them just out of the camera. The bottom row has had noise reduction added in post production.
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