The Old And The

I have had this discussion with many photographers, and very often the reaction to the proposition that the ISO control is redundant seems to cause dismay The reason, I think, is that most photographers have had a technique drummed into them that it is vital to find the 'correct' exposure and also that the primary function of the exposure controls is to adjust output mage density. The demonstration on the right shows that this is not necessarily the case, which means that many of 3 photographer's tacit assumptions no longer hold. In case we're throwing the baby out with the bath water, it's worth considering how photography mignt work without the ISO control. But before we do that, let's think about how it works with the ISO control.

Usinc a conventional camera, the first thing a ohotographer needs to do is make a guess at the likely levels of exposure in the picture to be taken and choose an appropriate ISO sensitivity. This choice establishes a target exposure and the photographer then has to balance that target exposure ¿gainst the required depth cf field and motion blur by finding exposure settings that centre the meter, either manually cr by use of an automatic exposure mode f an acceptable balance isn't found, then the photographer must decide :o make an adjustment to the ISO setting, usually upwards, lowering exposure and resulting in more noise

Usinc an 'ISO-ess' camera, the procedure of taking a photograph is rather simpler No initial guess at the likely exposure is necessary; the photographer just sets the aperture for the required depth of field and the shutter for the required motion blur. A check of the exposure meter is needed to see if the resultant exposure is large enough to meet the photographer's noise requirements If not, then a compromise must be made in either depth of field 011notion blur to yam more light.

Apart from a simplification in technique, the ISO-less method may also produce higher quality images. Remember that image noise levels are absolutely dependent on exposure: the more light in an image, the less noise it will have The conventonal technique will often result in unnecessary reduction in exposure to match the pre-guessed exposure, or to ensure that the exposure lies on some standard ISO scale. This reduction inevitably results h more noise in the image than there needs to oe.

So it appears that the loss of the ISO control offers the potential to simplify and improve photography, but at the cost of a major change in mindset for many photographers.

HOUSTON, WE HAVE A PROBLEM

There is, however, a major problem with trying to take photographs the ISO-less way, and that problem is that camera controls are simply not designed to work that way. The whole operation of a camera is designed around the idea o' pre-guessing the likely exposure and then trying to achieve it It isn't just that cameras are not all ISO-less like the Nikon D7000; to a large extent, auto ISO modes can allow a similar style of operation. To name a few of the problems:

• If you use in-camera processing, the image density is controlled by the ISO setting, and if you use the ISO-less technique that density will be all over the place.

• Current cameras have exposure meters that don't tell you the absolute value of the exposure (as a traditional handheld meter would), they tell you the difference from correct' exposure as defined by your initial ISO setting, ard so are next to useless for ISO-less photography.

• Currently, photographers think about noise in terms of ISO, not exposure This is in itself not a problem. ISO is a proxy for exposure, and so if an exposure meter were designed to show the resultant ISO for a selected exposure, it would give the photographer the needed feedback about the likely noise in the image. Unfortunately, camera exposure meters do not do this. Howeve", the changes needed to a camera's user interface to make ISO-less photography easy are very small - and could even be added as a set of custom modes for photographers who prefer to work n that way. So far, no camera manufacturer offers such modes, but maybe, now that the Nikon D7000 lias shown ISO-less photography to be feasible over an exposure range of 6 stops or more, enough photographers will find the technique useful to make it worthwhile for camera manufacturers to include it in their feature lists.

^ - v bob NEWMAN originally trained as A a physicist and is now an engineer and computer scientist with a PhD in real-time f^l systems design. He has been working ' with the design and development of high-technology equipment for 35 years and has been responsible for innovative deveopments in graphics workstations, avionics, marine instruments and radar systems. Two of his products have won innovation awards. Bob has led research projects in design methodology, automotive technology and, more recently, sensing systems. He is currently Professor of Computer Science at the University of Wolverhampton. Bob is a camera nut and has been a keen amateur photographer from the age of seven. He is delighted to be given the opportunity to apply his professional expertise to his hobby.

The images below were taken with a D7000 and a D3S at 1/8sec at f/11 and ISO 6400. The bottom images use the same exposure (1/8sec at f/11), but with the camera set to IS0100. They have been adjusted to the same output density (apart from the highlights) in processing. In other words, they have been 'pushed' by 6 stops. Vou can see that while the images from the D7000 show little difference between the ISO 6400 and IS0100 versions, the D3S shows noticeably more noise when 'pushed'. The conclusion from this is that, so far as image quality is concerned, there is no reason to use the ISO control on the D7000, at least if you use a raw-based workflow.

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100 Photography Tips

100 Photography Tips

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