Andrew Talks Photography: A Funny Thing Called ISO

Catching actions shots just before sun-up or after sun-down in the African bush can actually be quite a challenging task, particularly when the action is in the shade of the bush. Getting a sharp picture, with little ‘noise’ is just near impossible. Here is the toss up. The players are shutter speed, aperture and ISO (sensitivity settings on your sensor).

Because we are into action we need to make the choice between high shutter speeds (Tv settings) freezing the exact moment in pin sharp focus or slowing it down and sacrificing sharpness for blurred movement. The first will reduce the inflow of light to the sensor and the other will blur movement (including movement of the camera, possibly to an unacceptable level), but also, perhaps, with greater artistic potential.

Due to low prevailing light, the propensity is towards opening up the aperture (Av setting) thus allowing more light to fall on the sensor, but this immediately shallows your depth of field, perhaps unrealistically to capture the entire incident unfolding in front of you. That incident will take a few second before the photo opportunity is lost.

The rescue here is your camera’s ISO settings. This is a carryover from the old days of film where film sensitivity was rated. The higher the ISO rating the more ‘grainy’ the film and the eventual picture developed there from. With today’s digital cameras the camera’s sensor may be adjusted for ISO sensitivity, just like film, and digital SLR cameras range between 100 and 3200, some even have an Auto-ISO function. Like film, the downside remains, the higher the ISO setting, the more noise can be detected in the eventual image, which can include colour distortion.

This image of lion and buffalo playing hide and seek around a tree might well be considered reasonably composed, and is a form of actions shot, but it falls down with the high incidence of image noise.  Look at the buffalo – blues and greens apparent.  Not one of my better shots, it was taken with a shutter speed of 1/125s at an aperture of f/5,6 and a very high ISO 1250. The perfectionist would easily pick at this for hours, but the sacrifice made to noise was the cost of getting the shot. I doubt the shutter speed could be reduced and the f stops were spot on. Of course, there is always the option of underexposing and using Photoshop to finesse the image.

In low light situations I do tend to use my camera’s auto-ISO function… it has often got me the shot.

One thought on “Andrew Talks Photography: A Funny Thing Called ISO

  1. Jolly lucky to be at the right place at the right time. ISO is a complex subject, can only speak from my experience with the Nikon D700. Recently at a school christmas panto in a hall, where the lighting was good for those on stage but fell away sharply for the audience some rows back. I wound the ISO up to 2400, resulting in a higher shutter. end result could be enlarged to A3 (16.535 x 11.68 (inches) without apparent noise.

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