The intention of this exercise is to experiment with ISO adjustments using scenes where adjusting ISO, and hence reducing exposure times, can help. Each series uses ISO Range -800,400,200,100.
This first sequence of images is simple demonstration of the benefit of being able to adjust exposure times by changing the ISO setting of the camera. At the highest ISO, where the camera’s sensor is the most sensitive to light, the main car in the image is sharp and had it not been for the other elements of the scene, it would have been hard to determine if the car was moving or not. However, once the sensor has been changed to it’s least sensitive setting, or lowest ISO, the exposure has increase to the point where lots of movement is captured.
ISO Range -800,400,200,100. Continuing from the point above, when hand holding the camera with no support, we can adjust ISO settings to make capturing an image possible. With these image, the light levels were not very and I deliberated set a narrow aperture of f/22. At ISO 100, this was giving a metered exposure of 1/3sec which clearly caused problems with unwanted movement. By the time the ISO had been raised to 800, the exposure had reached 1/20sec and seems to have lost the most of the signs of movement although reviewing the image at 100% it can still slightly be seen. However, the image still doesn’t seem to be overly sharp. As well as camera movement, the image may be suffering from diffraction due to the narrow aperture or is may also be noise (see below).
The three sequences above all show more examples of the affect of adjusting shutter speeds via the change in ISO, or sensitivity.
As well as looking at the effect on shutter speed when adjusting ISO, we need to consider noise. The images above show very little noise, especially at web resolutions, even at ISO 800 mainly due to the progression made in sensor technology.
However, improvements in sensor technology doesn’t mean that noise can be disregarded completely. When printing at A4 size, I’ve found that noise in images up to ISO800 is not really noticeable unless it is being looking for. However, printing the same image at 16×12 it can be seen but in the images I’ve printed at this size, I’ve not found it to be a problem. Also, improvements in today’s post processing software mean noise in images can be handled very effectively. I was happy recently with a score I received for an image taken at ISO3200 of a night time light show in a camera club competition.