Exercise 28 : Higher and lower sensitivity

This exercise required that a situation of marginal light be found and the impact of increasing sensitivity by increasing the ISO be investigated.  It was a dull and miserable day so an ideal opportunity to take some photographs at ISO50 and then repeat the same shot at ISO values up to ISO12800 which are available with the Canon 5DII.  It is easy to see from the exif data on each shot that as the ISO sensitivity is increased by one stop, then the shutter speed decreases to maintain the ‘correct’ exposure.  AT ISO50 the shutter speed was 1/30sec, rising to 1/250sec at ISO400, 1/1000sec at ISO1600 and finally a shutter speed of 1/8000sec was achieved at ISO12800.  All very well, but the noise that is introduced in the image also increases with sensitivity, which was largely the point of the exercise.  Noise ‘speckling’ depends on the sensor and processing technology on board with the camera, but I know from previous experience with the Canon 5DII that ISO800 shows very little noise in the shadows, but I have never pushed it to ISO12800 for any reason in my own photography.  In this exercise I coupled the 5DII with the Canon 70-200 f/2.8 L IS lens set at 70mm and some of the images are shown below.

The shots I took were of a simple garden scene in the rain and I have included selected shots here before exploring the shadow detail in the images to evaluate the noise.

ISO 100

ISO 200

ISO 400

ISO 800

ISO 1600

ISO 12800

On small  thumbnail images there appears on the face of it to be very little difference between the photographs, which does demonstrate that the negative image of noise in an image does depend on its intended use.  If its most important to get just any shot, as in some aspects of photojournalism maybe, then the graininess introduced probably does not matter.  Looking closely at the images I took, I have shown below the same close up section of the distant tree I the images taken at ISO50, 400, 1600, 6400 and 12800.  Although it is clear that the images change from the perspective of the visibility of the raindrops as shutter speed goes from 1/30sec to 1/8000sec (it was very heavy rain and the motion of the droplets ‘froze’ at around 1/250sec and ISO400) the main impact was on image quality through the increasing noise speckling.  At ISO6400 and 12800 the image clarity was severely compromised, although it was still clear what the subject of the image was.  Although various pieces of software exist to combat noise, both in programs such as Lightroom 4 and Photoshop CS5, as well standalone software such as Noise Ninja, there is little that can be done to rescue an image from this level of gross noise which is at its worst in the shadow areas of the image.

ISO 100 noise

ISO 400 noise

ISO 1600 noise

ISO 12800 noise

I wanted a set of images showing movement to explore the influence of changing sensitivity on shutter speed and therefore the extent to which action could be ‘frozen’, plus the need to explore the shadow detail and evaluate the level of noise introduced into the images as a result of using higher ISO values.  I took a series of images of a piece of copper sheet being cut into a circle with a jeweller’s saw.  The up and down sawing motion introduced a significant degree of movement and the dark background provided a suitable target to look for noise speckling.  I shot images at ISO values of 100, 200, 400, 800, 1600 and 3200 using the Canon 5DMkII and made no adjustments in post-production.  The shutter speeds increased from 1/6sec to 1/180sec as the ISO increased and the blur from the saw cutting can be seen to reduce as the shutter speed increased due to the increases made in the sensitivity via the ISO settings.

ISO 100

ISO 200

ISO 400

ISO 800

ISO 1600

ISO 3200

I increased the magnification of the top right hand corner of each image to expose the noise, as is shown below at ISO 200, 800, 1600 and 3200 and the significant increase in noise can easily be seen.  It depends on the intended use of a photograph and indeed the importance of its content as to whether the serious noise at high ISO setting actually matters or not, but for a general image such as this I would not go above ISO800 for a printed photo.

ISO 200 noise

ISO 800 noise

ISO 1600 noise

ISO 3200 noise

Increasing ISO sensitivity is a valuable tactic to enable the increase in shutter speed if that is required and f stop has been reduced to as low a value as possible or acceptable.  If there is a need to use a shutter speed of a certain value to freeze action, then increasing ISO is the approach to take if reducing f stop and underexposing do not fit the shooting situation.  Sensitivity is a major battleground between camera manufacturers these days and much advertising by the major brands is focused on who can take a great image at hugely high ISO values.  I think it has also been the areas where there has been the most recent technical development over the last few years of progression in the digital market.  The ability to change sensitivity in camera is of course a huge advantage in the digital age compared to the days of film when such a change would have required the loading of a different ISO film.