The objective of this exercise was to get us thinking about using different ISO settings and to consider when it would be appropriate to move away from the usual ISO100 setting. I remember as an 18 year old snapper being fascinated by the Kodak film adverts for different ISO films and thinking it would liberate me from those dreaded flash guns... ISO 400 was, alas, not enough to avoid flash in night photography! I did however, stumble across ISO1600 in 1994 in Italy and took some amazing shots in the Sistine chapel. These were taken without flash and it was absolutely amazing when I saw them once they had been developed. I also learnt that taking photos outside with such an high ISO led to very grainy pictures lacking in contrast. Here are some of the pictures.
The night photo along with the photos from the Sistine chapel allowed me to take the photos hand held without the use of flash and because thee was no sunlight, the grain usually associated with fast film was almost imperceptible. The daylight photo atop the Cupola tells a different story... it appears washed out, faded and the grain is very evident. Obviously not an ideal combination! Fast forward almost 20 years and we now have high ISO settings at the flick of a switch on our cameras. What hasn't changed though is that the higher the ISO setting, the more you have to compromise in terms of picture quality as image noise is introduced into the image.
For this exercise I took approximately 36 images at different settings (I am only loading a third of them). I decided to use a still life subject and increase ISO and aperture but maintain the shutter value constant at 1 second. I wanted to use different aperture settings to accentuate depth of field and of course the narrower the aperture, the longer the shutter would have to stay open. By increasing ISO and aperture values you can gauge how the three values interact and the compromises you have to make depending on what you are trying to achieve. For instance a narrow aperture at say f/11 or f/16 will give the greatest depth of field and maintain sharpness into the photo... but a small aperture also means longer shutter speeds (or higher ISO values) each bringing their own difficulties... long shutter speeds make it impossible to shoot hand held. A tripod is the order of the day. High ISO however creates noise... which is not quite as romantic as film grain.. in fact colour noise is probably the single most frustrating aspect of a photograph which usually ends up confining the photograph to the "cutting floor".
f/4.0: This is a fairly wide aperture setting and as such creates a shallow depth of field. The photos are all focused on the nutmeg and in the f/4.0 sets focus sharpness has already softened by the first orange half and by the second the image is sufficiently blurred to not be able to make out the segments within the orange. You will notice that image noise is very well controlled even if you view an enlarged section of the wine bottle. As the aperture is wide and the image is well exposed at ISO 100 there is no need to increase ISO to brighten the image. As you can see an increase in ISO by up to 4 stops only brightens the image and even if you only increase the ISO to 200 the image becomes overexposed. In order to maintain the same depth of field I would have to decrease the length of time that the shutter stay open. As ISO is increased progressively by 4 stops, to maintain the same exposure level at this depth of field with increasing ISO settings I would have to decrease the opening times of the shutters from 1 second by a stop for every full stop increase in ISO, i.e. ISO 200 would only need a 0.5 sec shutter speed; ISO 400 would only need 0.25 sec shutter speed; ISO 800 would need 0.125 and ISO 1600 would need a maximum shutter speed of 0.06 second or 1/10
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| ISO 100; Shutter speed 1". This photo is well exposed. |
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| ISO 200; Shutter speed 1" |
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| ISO 800; Shutter speed 1" |
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| ISO 1600; shutter speed 1" |
f/11: Aperture settings between f/11 and f/16 are considered the best aperture width for full frame cameras and which point they will capture the greater field of depth within an image before diffraction starts to soften image sharpness and so I decided to use these settings for the still life. In contrast to f/4.0 you will see that f/11 the depth of the focus now included the nutmeg, the first half orange and the cinnamon stick. The wine bottle and the steel ring however, are not sharply in focus but they are certainly clearer than at f/4.0. You will also notice that due the decreased size of the aperture letting less light in the image at ISO 100 is very dark. So dark in fact that the gold writing on the bottle cannot be made out so while the image has a greater depth of sharpness and no discernible image noise it is far too dark and underexposed. The right exposure only being achieved at about ISO 800 and by which point image noise has started to creep into the image in the form of colour noise that can be seen in the darker shades of the photo like the wine bottle. The noise is still well controlled but is the black is no longer pure. This noise differs from the noise of fast image film noise which is more of a grain and can add a pleasing effect. This noise however does not have the same effect.
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| ISO 100; Shutter speed 1" |
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| ISO 200; Shutter speed 1" |
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| ISO 400; Shutter speed 1" |
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| ISO 1600; Shutter speed 1" |
f/16: The best aperture setting for details and depth of sharpness should be a landscape photographers default "go to" setting, certainly if they are using a standard 35mm equivalent DSLR. But unless you are taking the photo in bright conditions ISO 100 with it's guaranteed of no image noise is useless. The photographs below are yet again staged at progressively higher ISO settings maintaining aperture and shutter values constant. Realistically, the only image that is usable in the set below is the one at ISO 1600 and again, this is far too high an ISO to realistically produce noise free images. Depth of field, however, is phenomenal. Most of the photo has been captured with maximum sharpness and while the noise is well contained, it is still visible in the blacks and detracts from the image.
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| ISO 100; Shutter speed 1" |
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| ISO 200; Shutter speed 1" |
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| ISO 400; Shutter speed 1" |
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| ISO 800; Shutter speed 1" |
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| ISO 1600; Shutter speed 1" |
Conclusion
Ensuring an image is well exposed and not unnecessarily distracting the ideal ISO setting to use would be a low ISO setting and a narrow aperture in instances where you want a sharpness throughout the image. This combination, however makes it difficult to take hand held photographs without rendering images useless on the grounds of a lack of sharpness caused by camera shake. Unless you are able to use a tripod the only way around this is to alter the ISO and aperture setting so that hand held shots are taken at a speed fast enough to overcome camera shake. If, on the other hand you wanted to isolate a subject and maintain only the subject in focus then you would aim for a wide aperture and as low an ISO as possible. This combination would facilitate using lower ISO settings because the wider aperture would allow more light to reach the sensor.
Whatever the settings, there arecompromises that you would have to consider and accommodate to the environment that you are photographing in. For instance, if the subject is sporting related and require a fast shutter speed above depth of field you would have to widen the aperture, thereby reducing depth of field and but increasing the amount of light that reaches the sensor and thereby ensuring that the photo remains bright. For a lot of sporting and wildlife photographs a shallow depth of field is ideal in that it will isolate the subject very effectively so this may not be too bad a compromise, whereas increasing ISO will introduce noise to a photograph which will detract rather than enhance the image. What then the lot of the landscape photographer? A steady hand or a tripod would probably be the best option. If the ultimate goal is to maximise depth of field then aperture needs to remain narrow and ISO should not be taken beyond a setting of 400, possibly 800.
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