I have always assumed that the relationship between ISO increases and Noise is linear. I seldom use the 1/3 f-stop setting on my camera - I just don't have a reason to fine tune down to the 1/3 of a stop.
I spent some time tonight testing the noise levels on my 1D Mark IV and found that noise is linear with an interesting exception. In the lower ISO range, the noise at 1/3 stop above the normal stop has much more noise. The noise at the 1/3 stop below the normal stop has less noise than the normal stop.
The chart below is arranged with blocks in the following order:
100
|
125
|
160
|
200
|
250
|
320
|
400
|
500
|
640
|
800
|
1000
|
1250
|
1600
|
2000
|
2500
|
3200
|
4000
|
5000
|
6400
|
8000
|
10000 12800
|
The noise in the blocks is highly amplified so that the visual relationships are more apparent.
As a result of this test, I intend to use ISO 160 and 320 more often.
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