Our mission; to create/find a scene that contains dark areas to photograph multiple times, changing the ISO settings for each picture.  The objective; to identify the difference in quality through visual observation and the noise readings provided by the camera.

Theoretically (and pretty obviously), the higher the ISO (keeping the aperture the same, to maintain an equal DoF), the poorer the quality of the picture.  So, at ISO 1600, for example, the picture quality will presumably be very grainy and less distinctive as the picture is blown up, whereas at ISO 100, the photograph should be of a considerably higher quality in comparison.

I decided to create a scene including a lit candle (to provide a good contrast between a well lit area, fading to darker parts of the frame), with fruit displayed in an arching pattern, furthering itself from the light and creating a good example of light to dark in a small space.  Below are my results, with noise readings alongside:














This is my lowest setting and as you can see the whole picture is of a good enough quality, consistently, to enlarge or zoom in without becoming blurry or pixelated, from the over-exposure of the flame, to the                                                                                                                          darkest part of the orange situated at the back.

Slightly less quality at ISO 200.  Whilst increasing the ISO I am decreasing the amount of time the shutter is open for to maintain the same exposure level, whilst keeping the aperture at f8 throughout the whole process.














As the experiment continues the theory comes to fruition that the image will become less defined and of a poorer quality the higher the ISO level.















A very distinct difference at ISO 800 from the previous shots.  Comparing ISO 100 to this picture shows an obvious variation in quality.















At the highest possible ISO (1600) it is clear to tell the reduction in quality.  The fruit at the back becomes less and less determinable as the experiment progresses.



To summarise, the higher the ISO level, the poorer the quality of the image, which is especially noticeable when the image is blown up or zoomed into.  It can sometimes be unavoidable to increase the ISO, hence why it is there, especially in low-light situations and when a flash does not want to be used.  Sometimes however, a higher ISO can create interesting effects when liaising with other settings.  For example, if a vintage style photo with a grainy finish and possibly some luminance is what you are after, a high ISO could contribute to this considerably.