Tuesday, 6 September 2011

Light: Project - The intensity of light

Exercise: Higher and lower sensitivity

Aim:  The aim of this exercise is to investigate the difference in using a range of ISOs and the trade off between being able to take a shot and the noise levels in the image.

Approach and results:

I started by using ISO 100 in as lower light as possible to the point where I was relying on the image stabilisation for some of the shots and on close inspection there was still some movement.  The images only really became pin sharp at ISO 800.  I took the same shot using ISO 100 to ISO 3200.  In reducing the images for the blog any close-up comparison is impossible as there is no longer enough detail to compare.  Therefore I have sampled some of the areas in the images.

For the first example I chose an image with a range of colours and have enlarged ISO400 and ISO3200.  ISO400 shows no noise in any areas.  800 was slightly sharper but there were some speckles creaping in under close inspection.  1600 was noisier still and 3200 was the worst.  It was most noticable in the soft, out of focus areas.  The grey or midtone areas also show more noise.  Blacks were handled quite well which is surprising.  Any large plain area had a tendency to highlight noise.  That said, even the 3200 when viewed normally was far better than I expected and probably usable to a reasonable size.  I would have thought this would be limited to small web images but this exercise has changed my mind. 


ISO 400

ISO 3200

For the second example I have enlarged ISO100 and ISO800.  As this is a close up shot I needed a small aperture to get the required depth of field.  The result is that ISO100 is not fast enough to keep the image sharp.  ISO800 is a far better result and a more usable image with very little if any noticable noise introduced.


ISO 800 (top) and ISO 100 (bottom)

I also tried the multi frame noise reduction option on my camera which works at all ISOs and takes a series of images to reduce noise.  This worked very well and is a useful tool for low light static images.

Learning points:

I don't need to be too worried about using higher ISOs and I can be much more flexible with the ISO range that I use rather than generally leaving it on 200 and using maximum apertures.
In scenes with large plain areas it is worth using as low ISO as you can as this is where it becomes most obvious.
A slight amount of noise will always be preferential to a blurred image.
This does not make me want to use auto ISO as I still want to know what ISO is being used.

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