In my last article I listed some of the techniques I use for photographing industrial farming documentary portraiture and documentary still life. In the next couple of articles I want to explore the first techniques on the list: available light techniques.
I am starting with the first technique on the list: high ISO. This week I took some test shots in a working dairy shed of milking cups varying the ISO while maintaining the aperture at f2.8. Analyzing these photographs has led to what will be the subject of my next trial and article: Auto-ISO in Manual Mode.
This article looks at tests that manually vary the ISO while photographing a set of milking cups lying on a concrete floor in dairy shed during the day. Each image at each ISO has a section cropped and enlarged to exam grain and sharpness.
Herring bone milking sheds are physically constrained sites for photography with constant movement of subjects ( people and cows ), pipe work and hoses to navigate and unpredictable discharges or urine and manure. The light is generally poor for photography with objects inside the shed becoming dark shadows against the burnt-out highlights of the outside daylight. The photographs often need to be taken from within the pit, a central concrete trench that the milker stands into attach, detach and transfer the cups between rows of cows.
Rotary sheds are easier to photograph in, especially if they have large openings, doors or even donut shaped roofs.
The image below of a technician vaccinating in the pit was shot with available light within the pit of the herring bone milking shed then developed in Lightroom to bring out more detail in the technician. ( My goal when choosing the ‘correct’ exposure is to ensure that there is detail in the white surgical gloves. ) The lighting and operational constraints within a pit can be seen.

These photographs are generally documentary portraiture or documentary still life. They require sufficient but relatively shallow depth of field of at least 600mm. Unless a specific effect is required a shutter speed need to be no greater than the minimum hand holding speed. This makes Nikon Auto-ISO a good tool to manage the exposure settings.
Shooting in aperture priority Nikon Auto-ISO will select the shutter speed down to the minimum shutter speed specified then increase the ISO. A 24mm lens @ f8 on a Nikon Z6 focused at 1 meter will have depth of field from 0.78 meters to 1.4 meters. That sets the minimum aperture as f5.6. Setting the aperture to f8 increases the depth of field from 0.6 meters to 1 meter.
Below is a series of test shots from ISO 100 to ISO 12800 shot squatting in a milking pit while the cows were being pregnancy tested using ultrasound. Throughout the shoot there was regular splattering’s of cow manure onto my back and into my hair. The camera was handheld and the ISO manually changed by 1 EV to create a series. F2.8 was chosen as the constant aperture to create a clearly defined focus area and autofocus used in spot mode. The test shot at ISO 6400 was discarded because the focus point was far from the rest of the series.
The next step is to do a test using Nikon Auto-ISO at f5.6 & f8 in a more dynamic shooting style. Trying in both Manual and Aperture Priority modes.
1/15 second at f2.8, ISO 100
Visible camera shake at 1/15 second. The focus plane is on the droplet on the black hose but nothing is sharp due to camera movement. Neither the camera or lens have image stabilization and I would not expect myself to handhold successfully at 1/15. I was squatting in the pit and resting my elbows on the concrete platform.

1/40 second at f2.8, ISO 200
ISO 200 is sharper and grain is not intrusive but 1/40 is slower than I would hand hold if I was not braced against an object.

1/80 second at f2.8, ISO 400
At ISO 400 grain still not intrusive but in this test visible camera shake at speeds below 1/80 second.

1/160 second at f2.8, ISO 800
Grain becoming more visible at ISO 800 but I would feel happy that I could hand hold without support at 1/160. The pixel dimensions of the image are sufficient to print it out at A2 and I would be comfortable that the grain would not be too intrusive at this ISO.

1/250 second at f2.8, ISO 1600
ISO 1600, the grain is becoming more obvious but not intrusive not does it blur image details too much.

1/640 second at f2.8, ISO 3200
1/640 second at f2.8, ISO 3200. At ISO 3200 , compared to ISO 1600, the grain is large enough to start blurring the visual boundary between the two stainless bodies of the cups. For comparison the water drops on the black hoses are sharp and in focus in both the ISO 1600 and ISO 3200 crops. This merging of the stainless steel cup bodies is even worse at ISO 12800.

1/3200 second at f2.8, ISO 12800.
ISO 12800 is unusable for documentary still life but maybe acceptable for portraiture if it aligns with subject and style. That could communicate a feeling of being real and immediate and intimate.

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