Time for a programmed-ISO mode on DSLRs

Last Thursday I was taking a picture of a sunset when suddenly a policewoman went past on a Segway. So breaking off from the sunset I tried to take a quick snap of policewoman on Segway in the few seconds before she was gone.

Shots like that are always something of a hit and miss affair, this one missed. Even with a VR lens, it is not possible to take decent hand-held shots indoors at ISO-200 and f/5.6 without flash.

Which got me thinking about the fact that the controls on my Nikon D300 are essentially the same as the controls on my Nikon N90s which in turn only added an aperture priority mode from my Nikon FG, now 25 years old. Given a shutter speed the D300 will chose the aperture or given the aperture it will chose the shutter speed or in program mode the camera will set both automatically or neither in manual mode.

But the exposure on a camera, whether digital or film based is determined by three camera settings (and the available light): the aperture, shutter speed and the ISO setting.

On a film camera the ISO setting is determined by your film stock, once set you can only change it by changing the film. But on a digital camera the 'ISO setting' is actually the gain setting on the A-to-D converters inside the camera and that can be changed on every exposure.

In most shots I have a very definite opinion about the aperture: usually either wide open to minimize depth of field or set to the diffraction minimum to maximize depth of field. In certain shots I also have a particular opinion about the shutter speed. The ISO setting does have some impact on the end result of course, but with the introduction of modern CMOS sensor cameras like the D300, this is generally much less of a factor than the aperture or shutter speed.

So here is my question: why not have a new program mode in which the camera uses the ISO setting to adjust to the available light?

The D300 does have an 'Auto-ISO' mode but it is nowhere near as easy to use as the other camera modes. I simply cannot predict whether the camera will adjust to the light level by changing the ISO setting or the shutter speed setting which makes it not very useful.