Figure 6-30: The last three ISO values have bars surrounding them. That means these are not ISO values that are native to the sensor.
If you don’t care for the fixed limits of Auto ISO described above, your camera actually allows you to customize both the low and high boundary of what the camera will choose while in Auto ISO. When in the ISO menu and you’ve selected Auto, just use the Right arrow to move to the right. Hitting UP and DOWN now will change your minimum AUTO ISO value; then move to the right once more and you’re adjusting your Maximum Auto ISO. Notice that with this feature you can set the upper end of ISO as high as 51,200 (which I strongly discourage). I keep mine set to between 100 and 3200 for casual shooting. I’ll set the ISO to something higher (and switch to RAW mode or MFNR mode) when there’s just no other choice.
Notice that the last three ISO choices ("32,000", “40,000”, and "51,200") have bars above and below them, as seen in Figure 6-30. Why the bars?
Figure 6-30: The last three ISO values have bars surrounding them. That means these are not ISO values that are native to the sensor. |
The short answer is that this CMOS sensor actually has a native hi-end speed of 25,600. The last three values just amplifies the signal, resulting in disproportionally more noise than if the sensor had those speeds natively. This isn’t a bad thing unless you push it to far, like how Nikon achieved 7-figure ISO values in their latest D5. :-)
This is one of those technical things that you really don’t need to know. The mantra “The higher the ISO, the greater the noise” still applies.