Category Archives: 16. The intensity of light

Higher and lower sensitivity

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.

Image 1

 I shot this scene of the River Kelvin in Glasgow, first with ISO 100 then again with ISO 1000.

36mm, f/5.6, 1/500s, ISO 100

1. 36mm, f/5.6, 1/500s, ISO 100

29mm, f/5.6, 1/4000s, ISO 1000

29mm, f/5.6, 1/4000s, 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.

ISO 100

ISO 100

ISO 1000

ISO 1000

The difference in the degree of noise between ISO 100 and IS0 1000 is very noticeable; with the latter appear very grainy and speckled.

Image 2

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.

50mm, F/5.6, 1/350s, ISO 100

50mm, F/5.6, 1/350s, ISO 100

ISO 1000

50mm, f/5.6, 1/4000s, ISO 1000

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.

ISO 1000

ISO 1000

ISO 100

ISO 100

Image 3

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.

26mm, f/5.6, 1/125s, ISO 100

26mm, f/5.6, 1/125s, ISO 100

26mm, f/5.6, 1/2000s, ISO 1000

26mm, f/5.6, 1/2000s, 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.

ISO 100

ISO 100

ISO 1000

ISO 1000

Image 4

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.

ISO 100

ISO 100

ISO 1000

ISO 1000

ISO 2000

ISO 2000

ISO 6400

ISO 6400

ISO 6400 at 66.6%

ISO 6400 at 66.6%

Image 5

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.

ISO 100

ISO 100

ISO 1000

ISO 1000

ISO 2000

ISO 2000

ISO 6400

ISO 6400

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.

ISO 100

ISO 100

ISO 6400

ISO 6400

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.

Conclusion

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
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Measuring exposure

Measuring exposure

What is exposure?

Präkel (2009) defines exposure as the ‘combination of intensity and duration of light used to allow the right amount of light to reach film or sensor to record full tonal range’. He also raises the question, ‘what is good exposure?’ (2009, p20). He advises that good exposure can be the exposure that is technically correct, showing detail in the darkest shadows and detail in the brightest highlights. However, he notes that good exposure can also be the exposure that feels right to the photographer and look right in the final print.

The first exercise in Part Four-Light, deals with measuring and controlling exposure. 

The exercise comprises two parts as follows-

Part One- Produce four and six photographs which are deliberately lighter or darker that average, and say why in you written notes.

Part Two- Take five or six different photographs; of any subject, but for each one make five exposures, arranged around what you have measured as the best exposure. Consider if the central exposure is what you wanted and if any of the other exposures are acceptable too.

Part one

Fireplace-

This is a photograph of an artificial leaf and flower arrangement against an iron and ceramic tiled fireplace. I used the TTL spot meter to take a reading off the green leaf and this suggested a 1/6s shutter speed alongside an aperture of f/4 and ISO of 100.

Fireplace

Fireplace

However, when I viewed the image on my laptop screen I realised that the detail on the ironwork inside the fireplace was barely visible; therefore I added some shadow fill in post-processing.

Perhaps as the sun was hitting the leaf it would have better to spot meter off the dark green tile or alternatively I could have experiment with a higher ISO?

Screen Shot 2013-11-21 at 11.35.07 AM

fireplace histogram

On first look it doesn’t strike me as appearing as an overly dark image, however the histogram shows a chart skewed strongly towards the left noting that the image is composed of mainly dark tones.

Window-

Because of the range of bright and darker areas in this image I, again, opted for spot metering to gauge the exposure. I metered off the green foliage in the background to set the shutter speed at 1/350s alongside the aperture of f/4.2 and ISO 100. Rather unsurprisingly, the histogram shows the image as being brighter than average with the pixels distributed towards the right side of the graph.

window histogram

window histogram

Ivy on fence-

I spotted this ivy trailing over a neighbours fence and though this would qualify as a subject that is darker than average. With a wide aperture of f/4 and ISO of 100, I measure the exposure of this scene using the matrix metering setting and set the shutter speed to 1/90s. This produced a very dark scene with some blocked shadows. I applied some shadow fill in post processing to recover these.

ivy on fence

ivy on fence

ivy histogram

ivy histogram

Fence post in park-

This photograph was taken in a park on a very bright, sunny day and shows both dark and light areas. I spot metered off of the dark foliage and recomposed to focus on the post.

Fence post in park

Fence post in park

While the histogram shows that the pixels stretch across the shadows, mid-tones and highlights, the bunching of pixels at the right end of the graph show that the highlights are close to being ‘blown-out’.

fence post histogram

fence post histogram

Lion on railings-

A close up view of park railings and background foliage created this ‘dark’ photograph. As the scene was not high-contrast I used matrix-metering to set the exposure at 1/30s, f/4.5 and ISO 100.

Lion's head on railing

Lion’s head on railing

The left skewed histogram shows the pixel distribution in the image is skewed towards darker tones. However, the exposure managed to capture the scene without blocking the shadows.

railing histogram

railing histogram

Part two

This section looks at the way adjusting the exposure will affect an image. The images are JPEGs and have not had their exposure adjusted in post processing.

Image 1– I took these photographs of the Trinity building in Glasgow with the aperture open to f/11 and ISO set to 100. Using matrix metering the TTL exposure meter suggested a shutter speed of 1/250s. I then took at series of 5 shots at ½-stop intervals, one at the recommended exposure, two above and two below. The results are below.

1 stop brighter, 1/90s

+ 1 stop, 1/90s

1/2 stop brighter, 1/125s

+1/2 stop, 1/125s

Suggested exposure, 1/250s

Suggested exposure, 1/250s

1/2 stop darker, 1/350s

– 1/2 stop, 1/350s

 

 

 

 

1 stop darker, 1/500s

-1 stop, 1/500s

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At + one stop the colours of the stone appear washed out and the sky is a much lighter blue than the scene originally was. The +½ stop brighter exposure seems to have worked out quite well as there is detail in both the shadow and the highlights. At the exposure recommended by my camera the blue of the sky is a better match to the sky in the original scene, however the front of the building is in the shade and looks overly dark.

The darkness increases at both -½ stop and -1 stop resulting in lost details in the shadows.

It would seem that the exposures that worked best for this scene are the in-camera recommended exposure and ½ stop brighter.

Image 2-

I repeated this exercise using these hydrangea as the subject. It was an outdoor scene on a slightly overcast day. With the aperture set to f/5 and ISO 100 the in-camera exposure meter recommended a shutter speed of 1/500. Therefore +1 stop equalled 1/180s, +1/2 stop 1/350s, -1/2 stop 1/750s and -1 stop 1/500s.

+1 stop, 1/180s

+1 stop, 1/180s

+1/2 stop, 1/350s

+1/2 stop, 1/350s

 

 

 

 

 

 

 

 

+1 stop renders the image too bright; the detail in the flower petals is lost and the green foliage is very pale. +1/2 stop is a more acceptable exposure, as more detail is visible in the flower petals.

suggested exposure, 1/500s

Suggested exposure, 1/500s

-1/2 stop, 1/750s

-1/2 stop, 1/750s

 

 

 

 

 

 

 

-1 stop, 1/1000s

-1 stop, 1/1000s

 

 

 

 

 

 

 

 

 

The in-camera recommended exposure works well for the blue of the flowers as of the five exposures; this is the closest match to the original scene. At -1/2 stop the background the overall image is darkened and has a gloomy appearance while at -1 stop the details are lost in the shadows. Of the five images I prefer the 1/500s image, which was the in-camera’s recommended exposure.

Image 3- I spotted this flowering plant on a bright summer’s day, as it seemed to attract a large number of insects, particularly butterflies. The scene varied slightly between each shot as the butterfly moved across the flower. At 55mm, f/5.6 and ISO 100 the shutter speeds were as follows +1 stop 1/125s, +1/2 stop 1/180s, in-camera recommended shutter speed 1/250s, -1/2 stop 1/350s and -1 stop 1/500s.

+ 1stop, 1/125s

+ 1stop, 1/125s

+1/2 stop, 1/180s

+1/2 stop, 1/180s

suggested exposure, 1/250s

suggested exposure, 1/250s

-1/2 stop, 1/350s

-1/2 stop, 1/350

-1 stop, 1/500s

-1 stop, 1/500s

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+1 stop is very bright and this has bleached out the small details in the large flower head, making it appear white. + ½ stop is better and a little more light pink colour can be seen in the flower. The orange of the butterfly is also more saturated. The in-camera recommendation of 1/250s seems to work quite well as the colours are bright and the details in the flower and leaves can be seen.

However, the -1/2 stop exposure has allowed the small details to become even more defined and the colours of the foliage darker and more natural. At -1 stop the shadows increase and the overall image is darker, appearing more like a dull overcast day that a sunny day. In this instance, I feel that both the in-camera and the -1/2 stop settings worked best.

Image 4- I took these photographs of a stone balustrade covered in ivy on a slight cloudy, but still bright day. At 26mm, f/4.2 and ISO 100 the in-camera’s suggested shutter speed was 1/125s.

+1/2 stop, 1/90s

+1/2 stop, 1/90s

+ 1 stop, 1/60s

+ 1 stop, 1/60

suggested exposure, 1/125s

suggested exposure, 1/125s

-1/2 stop, 1/180s

-1/2 stop, 1/180

-1 stop, 1/250s

-1 stop, 1/250s

At +1 stop (1/60s) the scene is clearly overexposed. Details in the leaves and texture in the stone has been lost in the highlights. +1/2 stop (1/90s) is also too bright; the colours are bleached and there is very little contrast. A 1/125s has given the greens a little more saturation, however the image still looks too bright. At -1/2 stop the texture of the stone is becoming more visible and the shape of the individual leaves are becoming more defined. The -1 stop image is actually my preferred exposure of the five as it has more contrast and detail. There are a few small areas that are quite dark however, which made me wonder if adjusting the exposure in increments of 1/3 of a stop and applying a -2/3 stop would have worked even better?

Image 5– This is, again, the Trinity building, Glasgow, from a different angle. At 36mm and ISO 320, I dialed in an aperture of f/11. On hindsight, a lower ISO would probably have worked better as it was a bright, sunny day. The in-camera exposure meter suggested a shutter speed of 1/1000s.

+1 stop, 1/500s

+1 stop, 1/500s

+ 1/2 stop, 1/750s

+ 1/2 stop, 1/750s

suggested exposure,  1/1000s

suggested exposure, 1/1000s

-1/2 stop, 1/1500s

-1/2 stop, 1/1500s

-1stop, 1/2000s

-1stop, 1/2000s

 

 

 

 

 

 

 

 

 

+1 stop equalled a shutter speed of 1/500s, which renders the building a little washed out, and most of the brickwork pattern barely visible. At +1/2 stop the colours are a little warmer, although the brickwork detail is still barely perceptible. At 1/1000s the exposure seems to work well. The sky is a bright blue, brickwork detail (particularly in the tower) can be seen and the image transmits a sense of it being a bright summer’s day. Reducing the exposure by ½ stop to 1/1500s shutter speed also produces good colours, however it also darkened the shadow areas and gives the image a more ‘contrasty’ feel. -1 stop, 1/2000s has increased the contrast throughout the photograph, possibly a little bit more than suits my taste. I consider both the in-camera suggested setting of 1/1000s and the -1/2 stop image to work best for this scene. And again, wondered if adjusting the stop increments to 1/3s and applying a -1/3 stop would have worked have achieved a result somewhere between the two?

Conclusion

The results of this exercise have proven interesting as it illustrated the marked difference that even a slight adjustment in exposure can produce. Differences in colour, texture, details and contrast were all noted. The exercise has also shown me that while the in-camera exposure meter does a pretty good job of suggesting a ‘correct’ exposure, it cannot be blindly relied upon.