Higher and lower sensitivity
ISO stands for International Organization for Standardization, a body that sets standards for film speeds and matching digital sensitivity (Präkel, 2009). This exercise looks at the effects of raising the ISO in your camera. It asks for scenes to be shot at normal sensitivity, and then reshot at a higher sensitivity. We are asked to note if this made shooting easier and the overall effect on the image.
Raising the ISO increases a camera’s sensitivity to light. However, I was not fully aware of the degree to which the sensitivity is affected. The course notes state that by increasing the ISO from 100 to ISO 400, the camera becomes four times more sensitive to light, offering the option of using an aperture four times smaller or a shutter speed four times faster.
The camera I work with, a Nikon D5100, has an ISO range of ISO 100-6400. An ISO of 100-200 is, generally, considered to be an appropriate ISO for a bright, sunny day and this is what I use when taking photographs outdoors. When taking photographs indoors and under low light I will raise the ISO slightly, but never over 800 as I have tried to avoid the appearance of noise. In the glossary Präkel (2009) describes noise as ‘out of place pixels that break up the smooth tones in a digital image’. It adds a grainy appearance to an image and is common in digital photography with higher sensitivity settings.
I shot this scene of the River Kelvin in Glasgow, first with ISO 100 then again with ISO 1000.
I shot this scene of the River Kelvin in Glasgow, first with ISO 100 then again with ISO 1000 in Manual Mode, keeping the aperture constant. As it was a breezy day the weather changed frequently, alternating between overcast and bright.
The difference in the shutter speed recommended by my in-camera exposure meter was very noticeable, 1/500s at ISO 100 and 1/4000s at ISO 1000. Despite the shutter speed increasing the 2nd image is much brighter and the colour appear bleached. Perhaps, because at this point the day was relatively bright which negated the need for an increased ISO.
While noise cannot be detected by the eye at this size of print, I zoomed into a section of each image at 200% to note if it would be visible if the photograph was printed or displayed in a larger format.
The difference in the degree of noise between ISO 100 and IS0 1000 is very noticeable; with the latter appear very grainy and speckled.
I repeated the exercise with a photograph of a memorial statue in Kelvingrove Park. Increasing the ISO from 100 to 1000 meant that the in camera recommended shutter speed was much faster. The fast shutter speed allowed the movement of the girl on the bike on the bottom right of the frame and the three people on the left of the frame to be captured sharply.
I, again, examined the images at a 200% zoom to look for noise and noted that this was far more evident at the higher ISO sensitivity.
When I took image 3 the sky had become very grey and overcast. I took this photograph of a church sitting beside a fairly busy road, first at ISO 100 and then at ISO 1000.
ISO 100 and a 1/125s shutter speed captures the movement of the car as slightly blurred, whereas the increased sensitivity setting of ISO 1000 allows a faster shutter speed, 1/2000s, to be used which captures a car’s movement sharply. However, the increased ISO has resulted in some noise, which seems to lessen the contrast and make the black areas appear grey and grainy.
As the noise appears to be more noticeable on black areas in an image I selected a dark coloured subject, this statue erected in memory of the Glasgow cartoonist Bud Neill. The sky was very grey and overcast.
I took four shots with the ISO increasing from 100, to 1000, to 2000 and finally at 6400. The increasing ISO allowed faster shutter speeds to be selected, however at ISO 6400 noise is visible, even at this small size of image adding resulting in a loss of detail and contrast. This was even more noticeable at 66.6% zoom.
This image shows the rear side of a tenement block in Glasgow’s West End. It was taken on a dull, wet evening with low light. I opted for an aperture of f/16 to retain good depth of field and took four shots with ISO settings of ISO 100, ISO 1000, ISO 2000 and ISO 6400, adjusting the shutter speed as suggested by the in-camera exposure meter.
At ISO 100 the camera recommended a shutter speed of 0.3s. This shutter speed is too slow for a photograph taken hand held in this level of light and the results are a little soft.
Raising the ISO has allowed the shutter speed to become much faster ensuring a sharper shot. However, again noise is becoming visible as the sensitivity increases, particularly on the black of the drainpipe as can be seen in the screen shot of ISO 6400 above.
This has been an interesting exercise as it has forced me out my comfort zone by prompting me to experiment with higher ISO sensitivities. The results have shown that as raising ISO makes the camera more sensitive to light it provides the advantage of allowing smaller apertures and faster shutter speeds to be selected. Still the trade off seems to be noise in the image, particularly when it is displayed or printed in a larger size and/or when the ISO is raised very high. Having said that, I have opted to experiment with particularly high ISO sensitivities and now wonder if lower ISO’s such as 400, 640 or 800 would offer a more acceptable level of noise? This is something I will note when taking future photographs.
This exercise has illustrated that raising the ISO offers a photographer an increased number of creative options and is a useful additional to a toolkit.
- Präkel, D. (2009) Basics Photography: Exposure. Lausanne: AVA Publishing SA