Those "in-between" ISOs...

[Daniel Browning]

I find the the +1/3 tweeners ( 160,320,640...) better than shooting to the right with the normal ISOs.

The raw files have the exact same dynamic range and SNR, so if it's really any better it can only be due to issues with the raw converter, such as the problem mentioned above with DPP. Another example would be if the raw converter didn't have a good exposure compensation tool, like Adobe.

I started this because of the dark noise histograms provide by Peter Ruevski.

His read noise plots are fine, but they only account for Noise, not Signal. (By "signal", I'm referring to light, not the average level of the read noise.) ISO 160 only looks like less noise than ISO 200 because of a digital -0.33 EC. If Signal stayed the same, then ISO 160 would truly be better. But Signal doesn't stay the same: it goes down -0.33 with the noise, so the SNR stays the same.

I discovered this plot because of a post on dpreview where the poster was concerned with the amount of noise in a ISO 250 photo he had taken. Thats' because ISO 250 is 200 -1/3ev. It's essentially under exposed ISO 200 which increases the appereance of noise in the image. In fact, it looked worse than ISO400. Ruevski's plot confirms this finding.

Agreed.

I understand what you are saying Daniel, but I sometimes have to wonder whether you have real world data to back up the claims you continue to make on this subject.

I'll post a demonstration.

I have not seen personally any more overhead "dynamically" with ISO 100 images than ISO 160 images in all the time I've been post proccessing 40D RAW files.

A 1/3 stop difference in read noise is pretty hard to detect. Most of my shots aren't even within 1/3 of my ideal exposure, there just isn't time to get it perfect.

As far as combing in files, who cares? Just do a level adjustment in photoshop and watch the histogram get combed.

The combing is fine if you have a bunch of extra (wasted) bits. It would only be harmful if Canon was doing like Sony or Nikon and building them with just the perfect amount of precision.

If you want to put the camera on ISO 200 +.3ev, do it. Otherwise, you'll find ISO 160 0ev just as good and you won't have to think about it. In fact according to Ruevski you'll get 2/3ev faster shutter and a cleaner image than shooting ISO100.

Ruevski's chart correctly shows that the read noise in ADU is lower, but what really matters is SNR, and that is not improved over ISO 100 (in fact it's 1/3 stop worse).

And I'd rather have cleaner images than increased DR.

In this case, ISO 100 provides both.