For the first part of this exercise take similar shots at both normal and high sensitivity. Choose a situation which is marginal; that is where the mixture of light level and subject movement or depth of field is only just possible, eg a busy street market on an overcast day. Shoot first at normal sensitivity (ISO 100), then change to higher sensitivity (ISO 800).
Compare the two kinds of image close up (enlarge the digital view on the computer to 100%). Look in two kinds of area in the picture – those that are smooth, with little detail and neither particularly bright nor dark, and also in the deep shadow areas. What is the obvious difference?
For the sake of this exercise I have not done any post processing work, apart from the occasional crop. All the photos were taken during my lunch hour close to my office. For the most part I tried to get comparative images, but this proved a little difficult when photographing people walking down the sidewalk. However, I think, for the sake of this exercise, it worked quite well.
By increasing the ISO to 800 I was able to reduce my shutter speed by two and one-third stop allowing for quicker exposure. The exposure in fig 02 is overall brighter than fig 01, although I feel the brighter areas in fig 01 are a truer reflection of the actual building. When viewed close up, the noise increase in the lighter areas is not too bad, while the darker areas are really very noisy as can be seen in the closeup sections below.
With lighter coloured objects the increase in noise is definitely less noticeable. Again the image taken with the higher ISO is overall much brighter, even though it was a cloudy day and the photos were taken under a heavily shaded awning. The noise on the grey wall is fairly acceptable in fig 04, but the noise in the sign is very unpleasant when viewed close up. However, when viewed normally, it is fine. The side by side closeup comparisons are below.
With a busy street scene the difference between ISO 100 and 800 is more noticeable on the faces, especially with my camera as it is notorious for not taking great photos in low light, as is evident in the closeup portions of these two images below. The noise level in the dark areas is not attractive.
Shooting at ISO 100 (fig 07) caused a low shutter speed of 1/30 seconds and resulted in a motion blur while the man is walking along the side walk. At ISO 800 (fig 08) the girl’s stride is clear and frozen in time. Noise is less noticeable on lighter colours than dark.
Once again, at ISO 100 a lot motion blur was captured in fig 09 as my shutter speed was below my focal length, while fig 10 is sharper at the higher shutter speed and higher ISO.
I tried to follow this gentleman in the wheelchair with my camera to get similar shots, but unfortunately he was too fast for me while I was changing ISOs, so I had to shoot him from the back. In fig 11 there is a motion blur on the spokes of the wheels and well as on his hands as he turns the wheels. In fig 12 there is no blur at all. The noise level on this photograph is quite acceptable to me. It really is hit and miss with low light for my camera.
I’ve promised myself an camera upgrade once I’ve completed TAOP so that is something to look forward to. Definitely one of the “must haves” on the list will be a sensor that can cope with low light scenarios.