TAOP: Part 4 – Light: Exercise: Higher and lower sensitivity
March 22, 2012
This exercise is centred around adjusting sensor sensitivity – the ISO setting – in low light conditions in order to allow faster shutter speeds or a smaller aperture. As an example, switching from ISO 1oo to ISO 400 would allow for a four-times faster shutter speed, or a four-times smaller aperture.
Part One – Shots at different sensitivity
The first part of the exercise calls for a number of similar shots at normal and high sensitivity, in a marginal situation where the light and level of movement, or depth-of-field, make the image only just possible. I decided to shoot in the office at work.
I’ve picked out example shots that illustrate the impact of different sensitivity levels.
At ISO 100 the metering in the camera set the exposure to 0.4 seconds, so shooting with the camera in hand produced an image which suffered the effects of camera-shake.
A steadier shot for elements that are stationary, but with the shutter at 1/30 second the movement of the person in blue is still blurred.
Up at ISO 3200 the shutter speed is now sufficient – at 1/80 second – to prevent the blur of motion (so long as it’s not particularly fast).
At lower sensitivity it was impossible to get a clear image of the stationary elements of the sense. As the sensitivity increased that challenge was overcome, but it wasn’t until a big increase in sensitivity that it became possible to ‘freeze’ motion in the shot.
Part Two – Close-up comparison
This part of the exercise calls for a close-up comparison of the dark and mid-tone areas of the lower and higher sensitivity images.
The mid-to-dark areas suffer from extreme noise speckling (and the darker, the worse it appears) on the high sensitivity image, while they appear smooth in the low sensitivity shot.
Changing sensitivity is a compromise between catching elements of the shot and image quality – though it may be beneficial at times, for the purpose of adding a grained effect to ‘age’ a shot for artistic purposes.