Over the past year, I’ve noticed myself doing something I haven’t done before when setting camera exposures.  I’m also noticing others doing it - in fact others have been doing it for quite a while, seems I’m just catching on to the idea. Lately I read a message on a board that rang true ... exposure is now a triangle.

The reason is quite simple ... it’s the low noise performance of many of the current offerings from Canon and Nikon when using higher ISO’s(and perhaps others ... I’m not familiar with the capabilities of other brands).  In the days of film, your ISO choice (or ASA if you’ve been around as long as I have) was a decision you made before a shoot.  It was a tradeoff between film sensitivity and grain.  High ISO films were grainy, but often the grain was an acceptable and even useful effect to capture an image.  The only way you could use multiple ISO’s was with two cameras or camera bodies, or with multiple film backs if you used a medium format camera. Now, changing ISO is quick and easy.  In fact, with my new 1DsMark3, I can do it without taking my eye from the viewfinder in seconds. 

It appears that the use of ISO and it’s corresponding numbers was brought from the film world to make it easier for photographers to adapt.  I’m guessing it is just a reference point that photographers are familiar with, so settings are based on what one would expect from film.  It may have been just as easy to have sensitivity settings 1 through 6, and each increase is a 1 stop change, instead using the existing concept of film ISO.   A digital camera has a “base” or “natural” ISO, which is normally around 100.  Higher ISO settings are  achieved by amplifying the signal.  This process amplifies both components of the signal ... data and noise.  Noise tends to be more constant, so when you are amplifying the signal, you tend to have about the same amount of noise as you did at lower ISO settings, but far less data.  The result is a higher signal to noise ratio, resulting in .. you guessed it - more “digital” grain, or noise in the image.

Over the past few years one of the main objectives of those developing sensors for cameras has been to lower the noise, and recent cameras are an example of the realization of this goal.  The latest generations from Canon and Nikon have achieved a remarkable reduction in noise.  Post processing software has also dramatically improved the ability to remove or reduce noise in images.  The end result is an ability to use high ISO’s as a normal practice, instead of just when you absolutely had no other choice ... as a photographer you can use ISO almost as freely as using shutter speed and f-stop settings to control exposure.

The end result is far more freedom in exposure settings as you plan your shot.  If you find yourself getting to a shutter speed that is a little low, cranking up the ISO is a perfect solution.  This allows you to keep your f-stop in a range you are comfortable with ... whether your goal is control of depth of field, or maximum sharpness.

Medium format digital backs, while better, have not achieved the dramatic improvements found in DSLR’s, an in fact normally don’t even have the available options of a DSLR.  Of course, I don’t know many photographers that would haul their Hasselblad and P45 back to a motocross shoot.

So I would tend to agree with that internet poster, who probably heard that from some other internet web site ... exposure is now a triangle.