Understanding ISO sensitvity (Auto ISO)
Why this can help you in most cases.
About 1 year or so I purchased a Nikon D4S camera.
I found this good tip about "Auto ISO". The problem was that you need to put the camera in manual mode for this to work. However I tried using manual mode with the Nikon D300S and always ended up going back to aperture priority all the time. I guess it was not for me trying to work with the front and rear buttons all the time.
So I went out with the D4S for about a month or so to get used to the new camera at the time to see and to see images shot with an higher ISO and was surprised to see that I could a lot further with this camera then the Nikon D300S could. On the D300S I could not really go past 800 for good results. The D4S I found that I could surpass the ISO with good results at around 3200.
My game plain for my next outing was to use the auto ISO and turn it on in the camera and now select the maximum sensitivity to 3200 and the minimum shutter speed on the camera. Now once I made the changes, the next time out I was not going to turn the ISO feature off for a bit. Getting used to this took me a couple of days and now I use my camera most of the time on and turn it off in certain circumstances where I require it.
ISO adjustment is pretty straightforward with the D4, and the addition of being able to toggle Auto ISO on and off from the switches and dials works well. You can enable/disable Auto ISO by holding the rear-ISO button and then turning the Front sub command dial.
Here's how I really like to use Auto ISO though: I shoot in Manual mode! In manual mode I set the shutter, and the aperture. The Auto ISO will NOT enforce the focal length adjustment since the shutter speed is manually set. But it will cap the ISO at the max that has been set. The exposure will also be adjusted to + or - EV even though the camera is set to manual! The camera will operate like it does in aperture mode where EV is taken in to account, unlike in regular manual mode.
In Auto ISO and Manual exposure mode I control the shutter, the aperture and the exposure bias via the EV adjustment. The ISO will fluctuate up and down to meet the intended exposure. The ISO will be adjusted both up (as expected to boost sensitivity) and down (to not blow things out). This might be a bit unexpected, but it will allow you to go from say manual ISO at 400, to enabling Auto ISO and the resulting exposures might have ISO from 100 to 10,000!
Now I don’t have to worry about playing around with the ISO any longer. Also I should point out that you have one less thing to worry about and that is the constant setting of your ISO. I have more control now with setting the aperture and shutter speed to control the ISO settings range by adjusting the shutter speed as I tend to keep the aperture at what I would need. Remember to set your camera to what is acceptable for ISO noise and go out there and have some fun!